关键词：GIC、IAR、EOI、SGI/PPI/SPI、中断映射、中断异常向量、中断上下文、内核中断线程、中断注册。

1.1 ARM支持中断类型

ARM GIC-v2支持三种类型的中断：

SGI：软件触发中断(Software Generated Interrupt)，通常用于多核间通讯，最多支持16个SGI中断，硬件中断号从ID0~ID15。SGI通常在Linux内核中被用作IPI中断(inter-processor interrupts)，并会送达到系统指定的CPU上。

PPI：私有外设中断(Private Peripheral Interrupt)，是每个CPU私有的中断。最多支持16个PPI中断，硬件中断号从ID16~ID31。PPI通常会送达到指定的CPU上，应用场景有CPU本地时钟。

SPI：公用外设中断(Shared Peripheral Interrupt)，最多可以支持988个外设中断，硬件中断号从ID32~ID1019。

1.2 GIC检测中断流程

GIC（Generic Interrupt Controller,通用中断控制器）主要由两部分组成，分别是仲裁单元(Distributor)和CPU接口模块。

GIC仲裁单元为每一个中断维护一个状态机，分别是：inactive、pending、active and pending、active。

下面是来自IHI0048B GIC-V2规格书3.2.4 Interrupt handling state machine截图：

GIC检测中断流程如下：

(1) 当GIC检测到一个中断发生时，会将该中断标记为pending状态(A1)。

(2) 对处于pending状态的中断，仲裁单元回确定目标CPU，将中断请求发送到这个CPU上。

(3) 对于每个CPU，仲裁单元会从众多pending状态的中断中选择一个优先级最高的中断，发送到目标CPU的CPU Interface模块上。

(4) CPU Interface会决定这个中断是否可以发送给CPU。如果该终端优先级满足要求，GIC会发生一个中断信号给该CPU。

(5) 当一个CPU进入中断异常后，会去读取GICC_IAR寄存器来响应该中断(一般是Linux内核的中断处理程序来读寄存器)。寄存器会返回硬件中断号(hardware interrupt ID)，对于SGI中断来说是返回源CPU的ID。

当GIC感知到软件读取了该寄存器后，又分为如下情况：

* 如果该中断源是pending状态，那么转改将变成active。(C)

* 如果该中断又重新产生，那么pending状态变成active and pending。(D)

* 如果该中断是active状态，现在变成active and pending。(A2)

(6) 当处理器完成中断服务，必须发送一个完成信号EOI(End Of Interrupt)给GIC控制器。软件写GICC_EOIR寄存器，状态变成inactive。(E1)

补充：

(7) 对于level triggered类型中断来说，当触发电平消失，状态从active and pending变成active。(B2)

常用路径是A1->D->B2->E1。

1.2.1 GIC中断抢占

GIC中断控制器支持中断优先级抢占，一个高优先级中断可以抢占一个低优先级且处于active状态的中断，即GIC仲裁单元会记录和比较当前优先级最高的pending状态，然后去抢占当前中断，并且发送这个最高优先级的中断请求给CPU，CPU应答了高优先级中断，暂停低优先级中断服务，进而去处理高优先级中断。

GIC会将pending状态优先级最高的中断请求发送给CPU。

1.2.2 Linux对中断抢占处理

从GIC角度看，GIC会发送高优先级中断请求给CPU。

但是目前CPU处于关中断状态，需要等低优先级中断处理完毕，直到发送EOI给GIC。

然后CPU才会响应pending状态中优先级最高的中断进行处理。

所以Linux下：

1. 高优先级中断无法抢占正在执行的低优先级中断。

2.同处于pending状态的中断，优先响应高优先级中断进行处理。

1.3 GIC中断时序

借助GIC-400 Figure B-1 Signaling physical interrupts 理解GIC内部工作原理。

M和N都是SPI类型的外设中断，且通过FIQ来处理，高电平触发，N的优先级比M高，他们的目标CPU相同。

(1) T1时刻：GIC的总裁单元检测到中断M的电平变化。

(2) T2时刻：仲裁单元设置中断M的状态为pending。

(3) T17时刻：CPU Interface模块会拉低nFIQCPU[n]信号。在中断M的状态变成pending后，大概需要15个时钟周期后会拉低nFIQCPU[n]信号来向CPU报告中断请求(assertion)。仲裁单元需要这些时间来计算哪个是pending状态下优先级最高的中断。

(4) T42时刻：仲裁单元检测到另外一个优先级更高的中断N。

(5) T43时刻：仲裁单元用中断N替换中断M为当前pending状态下优先级最高的中断，并设置中断N为pending状态。

(6) T58时刻：经过tph个时钟后，CPU Interface拉低你FIOCPU[n]信号来通知CPU。因为此信号在T17时刻已经被拉低，CPU Interface模块会更新GICC_IAR寄存器的Interrupt ID域，该域的值变成中断N的硬件中断号。

(7) T61~T131时刻：Linux对中断N的服务程序--------------------------------------------------------------中断服务程序处理段，从GICC_IAR开始到GICC_EOIR结束。

　　T61时刻：CPU(Linux中断服务例程)读取GICC_IAR寄存器，即软件响应了中断N。这时仲裁单元把中断N的状态从pending变成active and pending。读取GICC_IAR

　　T64时刻：在中断N被Linux相应3个时钟内，CPU Interface模块完成对nFIQCPU[n]信号的deasserts，即拉高nFIQCPU[n]信号。

　　T126时刻：外设也deassert了该中断N。

　　T128时刻：仲裁单元移出了中断N的pending状态。

　　T131时刻：Linux服务程序把中断N的硬件ID号写入GICC_EOIR寄存器来完成中断N的全部处理过程。写GICC_EOIR

(8) T146时刻：在向GICC_EOIR寄存器写入中断N中断号后的tph个时钟后，仲裁单元会选择下一个最高优先级中断，即中断M，发送中断请求给CPU Interface模块。CPU Interface会拉低nFIQCPU[n]信号来向CPU报告外设M的中断请求。

(9) T211时刻：Linux中断服务程序读取GICC_IAR寄存器来响应中断，仲裁单元设置中断M的状态为active and pending。

(10) T214时刻：在CPU响应中断后的3个时钟内，CPU Interface模块拉高nFIOCPU[n]信号来完成deassert动作。

那么GICC_IAR和GICC_EOIR分别在Linux什么地方触发的呢？

1.4 Cortex A15 A7实例

2. 硬件中断号和Linux中断号的映射

2.1 硬件中断号：一个串口中断实例

2.2 中断控制器初始化

DTS中GIC定义于arch/arm/boot/dts/vexpress-v2p-ca15_a7.dts：

    gic: interrupt-controller@2c001000 {compatible = "arm,cortex-a15-gic", "arm,cortex-a9-gic";------------------此设备的标识符是"arm,cortex-a15-gic"#interrupt-cells = <3>;#address-cells = <0>;interrupt-controller;----------------------------------------------------表示此设备是一个中断控制器reg = <0 0x2c001000 0 0x1000>,<0 0x2c002000 0 0x1000>,<0 0x2c004000 0 0x2000>,<0 0x2c006000 0 0x2000>;interrupts = <1 9 0xf04>;};

struct irq_domain用于描述一个中断控制器。

GIC中断控制器在初始化时解析DTS信息中定义了几个GIC控制器，每个GIC控制器注册一个struct irq_domain数据结构。

struct irq_domain {struct list_head link;-------------------------用于将irq_domain连接到全局链表irq_domain_list中。const char *name;------------------------------中断控制器名称const struct irq_domain_ops *ops;--------------irq domain映射操作使用的方法集合void *host_data;unsigned int flags;/* Optional data */struct device_node *of_node;------------------对应中断控制器的device nodestruct irq_domain_chip_generic *gc;
#ifdef    CONFIG_IRQ_DOMAIN_HIERARCHYstruct irq_domain *parent;
#endif/* reverse map data. The linear map gets appended to the irq_domain */irq_hw_number_t hwirq_max;--------------------该irq domain支持中断数量的最大值。unsigned int revmap_direct_max_irq;unsigned int revmap_size;---------------------线性映射的大小struct radix_tree_root revmap_tree;-----------Radix Tree映射的根节点unsigned int linear_revmap[];-----------------线性映射用到的lookup table
}

struct irq_domain_ops定义了irq_domain方法集合，xlate从intspec中解析出硬件中断号和中断类型，intspec[0]和intspec[1]决定中断号，intspec[2]决定中断类型。

struct irq_domain_ops {int (*match)(struct irq_domain *d, struct device_node *node);int (*map)(struct irq_domain *d, unsigned int virq, irq_hw_number_t hw);void (*unmap)(struct irq_domain *d, unsigned int virq);int (*xlate)(struct irq_domain *d, struct device_node *node,const u32 *intspec, unsigned int intsize,unsigned long *out_hwirq, unsigned int *out_type);#ifdef    CONFIG_IRQ_DOMAIN_HIERARCHY/* extended V2 interfaces to support hierarchy irq_domains */int (*alloc)(struct irq_domain *d, unsigned int virq,unsigned int nr_irqs, void *arg);void (*free)(struct irq_domain *d, unsigned int virq,unsigned int nr_irqs);void (*activate)(struct irq_domain *d, struct irq_data *irq_data);void (*deactivate)(struct irq_domain *d, struct irq_data *irq_data);
#endif
};static const struct irq_domain_ops gic_irq_domain_hierarchy_ops = {.xlate = gic_irq_domain_xlate,.alloc = gic_irq_domain_alloc,.free = irq_domain_free_irqs_top,
};static int gic_irq_domain_xlate(struct irq_domain *d,struct device_node *controller,const u32 *intspec, unsigned int intsize,unsigned long *out_hwirq, unsigned int *out_type)
{
.../* Get the interrupt number and add 16 to skip over SGIs */*out_hwirq = intspec[1] + 16;--------------------------------------首先+16跳过SGI类型中断/* For SPIs, we need to add 16 more to get the GIC irq ID number */if (!intspec[0]) {-------------------------------------------------如果是SPI类型中断，还需要+16，跳过PPI类型中断。ret = gic_routable_irq_domain_ops->xlate(d, controller,intspec,intsize,out_hwirq,out_type);if (IS_ERR_VALUE(ret))return ret;}*out_type = intspec[2] & IRQ_TYPE_SENSE_MASK;---------------------中断触发类型，包括四种上升沿、下降沿、高电平、低电平。return ret;
}static int gic_irq_domain_alloc(struct irq_domain *domain, unsigned int virq,unsigned int nr_irqs, void *arg)
{int i, ret;irq_hw_number_t hwirq;unsigned int type = IRQ_TYPE_NONE;struct of_phandle_args *irq_data = arg;ret = gic_irq_domain_xlate(domain, irq_data->np, irq_data->args,irq_data->args_count, &hwirq, &type);---------------首先根据args翻译出硬件中断号和中断类型。if (ret)return ret;for (i = 0; i < nr_irqs; i++)gic_irq_domain_map(domain, virq + i, hwirq + i);---------------执行软硬件的映射，并且根据中断类型设置struct irq_desc->handle_irq处理函数。return 0;
}void irq_domain_free_irqs_top(struct irq_domain *domain, unsigned int virq,unsigned int nr_irqs)
{int i;for (i = 0; i < nr_irqs; i++) {irq_set_handler_data(virq + i, NULL);irq_set_handler(virq + i, NULL);}irq_domain_free_irqs_common(domain, virq, nr_irqs);
}

针对SPI类型中断，需要进行+16位移。

static int gic_routable_irq_domain_xlate(struct irq_domain *d,struct device_node *controller,const u32 *intspec, unsigned int intsize,unsigned long *out_hwirq,unsigned int *out_type)
{*out_hwirq += 16;return 0;
}

gic_irq_domain_map()入参有struct irq_domain和软硬件中断号，主要分SGI/PPI一组，SPI一组。

主要工作由irq_domain_set_info()处理，irq_domain_set_hwirq_and_chip()通过Linux中断号获取struct irq_data数据结构，设置关联硬件中断号和struct irq_chip gic_chip关联。

__irq_set_handler()设置中断描述符irq_desc->handler_irq回调函数，对SPI类型来说就是handle_fasteoi_irq()。

static int gic_irq_domain_map(struct irq_domain *d, unsigned int irq,irq_hw_number_t hw)
{if (hw < 32) {irq_set_percpu_devid(irq);-------------------------------PerCPU类型的中断有自己的特殊flag。irq_domain_set_info(d, irq, hw, &gic_chip, d->host_data,handle_percpu_devid_irq, NULL, NULL);set_irq_flags(irq, IRQF_VALID | IRQF_NOAUTOEN);} else {irq_domain_set_info(d, irq, hw, &gic_chip, d->host_data,handle_fasteoi_irq, NULL, NULL);set_irq_flags(irq, IRQF_VALID | IRQF_PROBE);gic_routable_irq_domain_ops->map(d, irq, hw);}return 0;
}void irq_domain_set_info(struct irq_domain *domain, unsigned int virq,irq_hw_number_t hwirq, struct irq_chip *chip,void *chip_data, irq_flow_handler_t handler,void *handler_data, const char *handler_name)
{irq_domain_set_hwirq_and_chip(domain, virq, hwirq, chip, chip_data);__irq_set_handler(virq, handler, 0, handler_name);irq_set_handler_data(virq, handler_data);
}int irq_domain_set_hwirq_and_chip(struct irq_domain *domain, unsigned int virq,irq_hw_number_t hwirq, struct irq_chip *chip,void *chip_data)
{struct irq_data *irq_data = irq_domain_get_irq_data(domain, virq);if (!irq_data)return -ENOENT;irq_data->hwirq = hwirq;irq_data->chip = chip ? chip : &no_irq_chip;irq_data->chip_data = chip_data;return 0;
}void
__irq_set_handler(unsigned int irq, irq_flow_handler_t handle, int is_chained,const char *name)
{unsigned long flags;struct irq_desc *desc = irq_get_desc_buslock(irq, &flags, 0);
...desc->handle_irq = handle;--------------------irq_desc->handler_irq和name赋值。desc->name = name;
...
}

drivers/irqchip/irq-gic.c定义了"arm,cortex-a15-gic"的处理函数gic_of_init，gic_of_init是GIC控制器的初始化函数。

IRQCHIP_DECLARE(cortex_a15_gic, "arm,cortex-a15-gic", gic_of_init);static int gic_cnt __initdata;static int __init
gic_of_init(struct device_node *node, struct device_node *parent)
{
...gic_init_bases(gic_cnt, -1, dist_base, cpu_base, percpu_offset, node);if (!gic_cnt)gic_init_physaddr(node);if (parent) {irq = irq_of_parse_and_map(node, 0);gic_cascade_irq(gic_cnt, irq);}if (IS_ENABLED(CONFIG_ARM_GIC_V2M))gicv2m_of_init(node, gic_data[gic_cnt].domain);gic_cnt++;return 0;
}

gic_init_bases的gic_nr是GIC控制器的序号，主要调用irq_domain_add_linear()分配并函数注册一个irq_domain。

void __init gic_init_bases(unsigned int gic_nr, int irq_start,void __iomem *dist_base, void __iomem *cpu_base,u32 percpu_offset, struct device_node *node)
{irq_hw_number_t hwirq_base;struct gic_chip_data *gic;int gic_irqs, irq_base, i;int nr_routable_irqs;BUG_ON(gic_nr >= MAX_GIC_NR);---------------------------gic_nr不超过系统规定的MAX_GIC_NRgic = &gic_data[gic_nr];--------------------------------struct gic_chip_data类型的全局变量gic_data，序号是GIC控制器序号
...
/** Initialize the CPU interface map to all CPUs.* It will be refined as each CPU probes its ID.*/for (i = 0; i < NR_GIC_CPU_IF; i++)gic_cpu_map[i] = 0xff;/** Find out how many interrupts are supported.* The GIC only supports up to 1020 interrupt sources.*/gic_irqs = readl_relaxed(gic_data_dist_base(gic) + GIC_DIST_CTR) & 0x1f;------------计算GIC控制器最多支持的中断源个数gic_irqs = (gic_irqs + 1) * 32;if (gic_irqs > 1020)-------------------------------------------------------GIC支持的最大中断数据，此处为1020gic_irqs = 1020;gic->gic_irqs = gic_irqs;if (node) {        /* DT case */const struct irq_domain_ops *ops = &gic_irq_domain_hierarchy_ops;--------------GICv2的struct irq_domain_ops
...gic->domain = irq_domain_add_linear(node, gic_irqs, ops, gic);-----------------注册irq_domain，操作函数使用gic_irq_domain_hierarchy_ops} else {        /* Non-DT case */
...}if (WARN_ON(!gic->domain))return;if (gic_nr == 0) {
#ifdef CONFIG_SMPset_smp_cross_call(gic_raise_softirq);register_cpu_notifier(&gic_cpu_notifier);
#endifset_handle_irq(gic_handle_irq);-------在irq_handler中调用handle_arch_irq，这里将handle_arch_irq指向gic_handle_irq，实现了平台中断和具体GIC中断的关联。}gic_chip.flags |= gic_arch_extn.flags;gic_dist_init(gic);----------------------GIC Distributer部分初始化gic_cpu_init(gic);-----------------------GIC CPU Interface部分初始化gic_pm_init(gic);------------------------GIC PM相关初始化
}

irq_domain_add_linear()->__irq_domain_add()分配并初始化struct irq_domain。

struct irq_domain *__irq_domain_add(struct device_node *of_node, int size,irq_hw_number_t hwirq_max, int direct_max,const struct irq_domain_ops *ops,void *host_data)
{struct irq_domain *domain;domain = kzalloc_node(sizeof(*domain) + (sizeof(unsigned int) * size),GFP_KERNEL, of_node_to_nid(of_node));-------------domain大小为struct irq_domain加上gic_irqs个unsigned int。if (WARN_ON(!domain))return NULL;/* Fill structure */INIT_RADIX_TREE(&domain->revmap_tree, GFP_KERNEL);domain->ops = ops;domain->host_data = host_data;domain->of_node = of_node_get(of_node);domain->hwirq_max = hwirq_max;domain->revmap_size = size;domain->revmap_direct_max_irq = direct_max;irq_domain_check_hierarchy(domain);mutex_lock(&irq_domain_mutex);list_add(&domain->link, &irq_domain_list);----------------------将创建好的struct irq_domain加入全局链表irq_domain_list。mutex_unlock(&irq_domain_mutex);pr_debug("Added domain %s\n", domain->name);return domain;
}

2.3 系统初始化之中断号映射

上一小节是中断控制器GIC的初始化，下面看看一个硬件中断是如何映射到Linux空间的中断的。

customize_machine()是arch_initcall阶段调用，很靠前。

customize_machine ->of_platform_populate ->of_platform_bus_create ->of_amba_device_create ->of_amba_device_create

下面结合dtsi文件看看来龙去脉，arch/arm/boot/dts/vexpress-v2m.dtsi。

/dts-v1/;/ {model = "V2P-CA9";arm,hbi = <0x191>;arm,vexpress,site = <0xf>;compatible = "arm,vexpress,v2p-ca9", "arm,vexpress";interrupt-parent = <&gic>;#address-cells = <1>;#size-cells = <1>;
...gic: interrupt-controller@1e001000 {compatible = "arm,cortex-a9-gic";#interrupt-cells = <3>;#address-cells = <0>;interrupt-controller;reg = <0x1e001000 0x1000>,<0x1e000100 0x100>;};
...smb {compatible = "simple-bus";#address-cells = <2>;#size-cells = <1>;ranges = <0 0 0x40000000 0x04000000>,<1 0 0x44000000 0x04000000>,<2 0 0x48000000 0x04000000>,<3 0 0x4c000000 0x04000000>,<7 0 0x10000000 0x00020000>;#interrupt-cells = <1>;interrupt-map-mask = <0 0 63>;interrupt-map = <0 0  0 &gic 0  0 4>,<0 0  1 &gic 0  1 4>,
...
/include/ "vexpress-v2m.dtsi"};
}vexpress-v2m.dtsi文件：motherboard {model = "V2M-P1";arm,hbi = <0x190>;arm,vexpress,site = <0>;compatible = "arm,vexpress,v2m-p1", "simple-bus";#address-cells = <2>; /* SMB chipselect number and offset */#size-cells = <1>;#interrupt-cells = <1>;ranges;
...iofpga@7,00000000 {compatible = "arm,amba-bus", "simple-bus";#address-cells = <1>;#size-cells = <1>;ranges = <0 7 0 0x20000>;
...v2m_serial0: uart@09000 {compatible = "arm,pl011", "arm,primecell";reg = <0x09000 0x1000>;interrupts = <5>;clocks = <&v2m_oscclk2>, <&smbclk>;clock-names = "uartclk", "apb_pclk";};
...};}

这里首先从根目录下查找"simple-bus"，从上面可以看出指向smb设备。

smb设备包含vexpress-v2m.dtsi文件，然后在of_platform_bus_create()中遍历所有设备。

const struct of_device_id of_default_bus_match_table[] = {{ .compatible = "simple-bus", },
#ifdef CONFIG_ARM_AMBA{ .compatible = "arm,amba-bus", },
#endif /* CONFIG_ARM_AMBA */{} /* Empty terminated list */
};static int __init customize_machine(void)
{
...of_platform_populate(NULL, of_default_bus_match_table,-----------------找到匹配"simple-bus"的设备，这里指向smb。NULL, NULL);
...
}int of_platform_populate(struct device_node *root,const struct of_device_id *matches,const struct of_dev_auxdata *lookup,struct device *parent)
{
...for_each_child_of_node(root, child) {rc = of_platform_bus_create(child, matches, lookup, parent, true);-----这里的root指向根目录，即"/"。if (rc)break;}
...
}static int of_platform_bus_create(struct device_node *bus,const struct of_device_id *matches,const struct of_dev_auxdata *lookup,struct device *parent, bool strict)
{const struct of_dev_auxdata *auxdata;struct device_node *child;struct platform_device *dev;const char *bus_id = NULL;void *platform_data = NULL;int rc = 0;/* Make sure it has a compatible property */if (strict && (!of_get_property(bus, "compatible", NULL))) {pr_debug("%s() - skipping %s, no compatible prop\n",__func__, bus->full_name);return 0;}auxdata = of_dev_lookup(lookup, bus);if (auxdata) {bus_id = auxdata->name;platform_data = auxdata->platform_data;}if (of_device_is_compatible(bus, "arm,primecell")) {------当遇到匹配"arm,primecell"设备，创建amba设备。在ofpga@7,00000000中创建uart@09000设备。/** Don't return an error here to keep compatibility with older* device tree files.*/of_amba_device_create(bus, bus_id, platform_data, parent);return 0;}dev = of_platform_device_create_pdata(bus, bus_id, platform_data, parent);if (!dev || !of_match_node(matches, bus))return 0;for_each_child_of_node(bus, child) {----------------遍历smb下的所有"simple-bus"设备，这里可以嵌套几层。从smb->motherboard->iofpga@7,00000000。pr_debug("   create child: %s\n", child->full_name);rc = of_platform_bus_create(child, matches, lookup, &dev->dev, strict);if (rc) {of_node_put(child);break;}}of_node_set_flag(bus, OF_POPULATED_BUS);return rc;
}

of_amba_device_create创建ARM AMBA类型设备，其中中断部分交给irq_of_parse_and_map()处理。

static struct amba_device *of_amba_device_create(struct device_node *node,const char *bus_id,void *platform_data,struct device *parent)
{
.../* Decode the IRQs and address ranges */for (i = 0; i < AMBA_NR_IRQS; i++)dev->irq[i] = irq_of_parse_and_map(node, i);
...
}

以uart@09000为例，irq_of_parse_and_map中的of_irq_parse_one()解析设备中的"interrupts"、"regs"等参数，参数放入struct of_phandle_args中，oirq->args[1]中存放中断号5，oirq->np存放struct device_node。

irq_create_of_mapping()建立硬件中断号到Linux中断号的映射。

irq_create_of_mapping主要调用如下，主要工作交给__irq_domain_alloc_irqs()进行处理。

irq_create_of_mapping ->domain->ops->xlate--------------------------------- ->irq_find_mapping ->irq_domain_alloc_irqs ->__irq_domain_alloc_irqs ->irq_domain_alloc_descs ->irq_domain_alloc_irq_data ->irq_domain_alloc_irqs_recursive ->gic_irq_domain_alloc ->gic_irq_domain_map-----------------------进行硬件中断号和软件中断号的映射 ->gic_irq_domain_set_info----------------设置重要参数到中断描述符中 ->irq_domain_insert_irq

unsigned int irq_of_parse_and_map(struct device_node *dev, int index)
{struct of_phandle_args oirq;if (of_irq_parse_one(dev, index, &oirq))return 0;return irq_create_of_mapping(&oirq);
}unsigned int irq_create_of_mapping(struct of_phandle_args *irq_data)
{struct irq_domain *domain;irq_hw_number_t hwirq;unsigned int type = IRQ_TYPE_NONE;int virq;domain = irq_data->np ? irq_find_host(irq_data->np) : irq_default_domain;---找到设备所属的struct irq_domain结构体。
.../* If domain has no translation, then we assume interrupt line */if (domain->ops->xlate == NULL)hwirq = irq_data->args[0];else {if (domain->ops->xlate(domain, irq_data->np, irq_data->args,-------调用gic_irq_domain_xlate()函数进行硬件中断号到Linux中断号的转换。irq_data->args_count, &hwirq, &type))return 0;}if (irq_domain_is_hierarchy(domain)) {-------------------------可以分层挂载/** If we've already configured this interrupt,* don't do it again, or hell will break loose.*/virq = irq_find_mapping(domain, hwirq);-------------------从已有的linear_revmap中寻找Linux中断号。if (virq)return virq;virq = irq_domain_alloc_irqs(domain, 1, NUMA_NO_NODE, irq_data);---------如果没有找到，重新分配中断映射。参数1表示每次只分配一个中断。if (virq <= 0)return 0;} else {
...}/* Set type if specified and different than the current one */if (type != IRQ_TYPE_NONE &&type != irq_get_trigger_type(virq))irq_set_irq_type(virq, type);-----------------------------设置中断触发类型return virq;
}

struct irq_desc定义了中断描述符，irq_desc[]数组定义了NR_IRQS个中断描述符，数组下标表示IRQ中断号，通过IRQ中断号可以找到对应中断描述符。

struct irq_desc内置了struct irq_data结构体，struct irq_data的irq和hwirq分别对应软件中断号和硬件中断号。通过这两个成员，可以将硬件中断号和软件中断号映射起来。

struct irq_chip定义了中断控制器底层操作相关的方法集合。

struct irq_desc {struct irq_data        irq_data;unsigned int __percpu    *kstat_irqs;irq_flow_handler_t    handle_irq;-----------------根据中断号分类，不同类型中断的处理handle。0~31对应handle_percpu_devid_irq；32~对应handle_fasteoi_irq。
#ifdef CONFIG_IRQ_PREFLOW_FASTEOIirq_preflow_handler_t    preflow_handler;
#endifstruct irqaction    *action;    /* IRQ action list */unsigned int        status_use_accessors;unsigned int        core_internal_state__do_not_mess_with_it;unsigned int        depth;        /* nested irq disables */unsigned int        wake_depth;    /* nested wake enables */unsigned int        irq_count;    /* For detecting broken IRQs */unsigned long        last_unhandled;    /* Aging timer for unhandled count */unsigned int        irqs_unhandled;atomic_t        threads_handled;int            threads_handled_last;raw_spinlock_t        lock;struct cpumask        *percpu_enabled;
#ifdef CONFIG_SMPconst struct cpumask    *affinity_hint;struct irq_affinity_notify *affinity_notify;
#ifdef CONFIG_GENERIC_PENDING_IRQcpumask_var_t        pending_mask;
#endif
#endifunsigned long        threads_oneshot;-------------是一个位图，每个比特位代表正在处理的共享oneshot类型中断的中断线程。atomic_t        threads_active;-------------------表示正在运行的中断线程个数wait_queue_head_t       wait_for_threads;
#ifdef CONFIG_PM_SLEEPunsigned int        nr_actions;unsigned int        no_suspend_depth;unsigned int        cond_suspend_depth;unsigned int        force_resume_depth;
#endif
#ifdef CONFIG_PROC_FSstruct proc_dir_entry    *dir;
#endifint            parent_irq;struct module        *owner;const char        *name;
}struct irq_data {u32            mask;unsigned int        irq;-----------------Linux软件中断号unsigned long        hwirq;--------------硬件中断号unsigned int        node;unsigned int        state_use_accessors;struct irq_chip        *chip;struct irq_domain    *domain;
#ifdef    CONFIG_IRQ_DOMAIN_HIERARCHYstruct irq_data        *parent_data;
#endifvoid            *handler_data;void            *chip_data;struct msi_desc        *msi_desc;cpumask_var_t        affinity;
}struct irq_chip {const char    *name;unsigned int    (*irq_startup)(struct irq_data *data);-------------初始化中断void        (*irq_shutdown)(struct irq_data *data);----------------结束中断void        (*irq_enable)(struct irq_data *data);------------------使能中断void        (*irq_disable)(struct irq_data *data);-----------------关闭中断void        (*irq_ack)(struct irq_data *data);---------------------应答中断void        (*irq_mask)(struct irq_data *data);--------------------屏蔽中断void        (*irq_mask_ack)(struct irq_data *data);----------------应答并屏蔽中断void        (*irq_unmask)(struct irq_data *data);------------------解除中断屏蔽void        (*irq_eoi)(struct irq_data *data);---------------------发送EOI信号，表示硬件中断处理已经完成。int        (*irq_set_affinity)(struct irq_data *data, const struct cpumask *dest, bool force);--------绑定中断到某个CPUint        (*irq_retrigger)(struct irq_data *data);----------------重新发送中断到CPUint        (*irq_set_type)(struct irq_data *data, unsigned int flow_type);----------------------------设置触发类型int        (*irq_set_wake)(struct irq_data *data, unsigned int on);-----------------------------------使能/关闭中断在电源管理中的唤醒功能。void        (*irq_bus_lock)(struct irq_data *data);void        (*irq_bus_sync_unlock)(struct irq_data *data);void        (*irq_cpu_online)(struct irq_data *data);void        (*irq_cpu_offline)(struct irq_data *data);void        (*irq_suspend)(struct irq_data *data);void        (*irq_resume)(struct irq_data *data);void        (*irq_pm_shutdown)(struct irq_data *data);
...unsigned long    flags;
}

gic_chip是特定中断控制器的硬件操作函数集，对于GICv2有屏蔽/去屏蔽、EOI、设置中断触发类型、以及设置或者当前芯片状态。

static const struct irq_chip gic_chip = {.irq_mask        = gic_mask_irq,.irq_unmask        = gic_unmask_irq,.irq_eoi        = gic_eoi_irq,.irq_set_type        = gic_set_type,.irq_get_irqchip_state    = gic_irq_get_irqchip_state,.irq_set_irqchip_state    = gic_irq_set_irqchip_state,.flags            = IRQCHIP_SET_TYPE_MASKED |IRQCHIP_SKIP_SET_WAKE |IRQCHIP_MASK_ON_SUSPEND,
};static void gic_mask_irq(struct irq_data *d)
{gic_poke_irq(d, GIC_DIST_ENABLE_CLEAR);
}static void gic_unmask_irq(struct irq_data *d)
{gic_poke_irq(d, GIC_DIST_ENABLE_SET);
}static void gic_eoi_irq(struct irq_data *d)
{writel_relaxed(gic_irq(d), gic_cpu_base(d) + GIC_CPU_EOI);
}static int gic_set_type(struct irq_data *d, unsigned int type)
{void __iomem *base = gic_dist_base(d);unsigned int gicirq = gic_irq(d);/* Interrupt configuration for SGIs can't be changed */if (gicirq < 16)return -EINVAL;/* SPIs have restrictions on the supported types */if (gicirq >= 32 && type != IRQ_TYPE_LEVEL_HIGH &&type != IRQ_TYPE_EDGE_RISING)return -EINVAL;return gic_configure_irq(gicirq, type, base, NULL);
}static int gic_irq_set_irqchip_state(struct irq_data *d,enum irqchip_irq_state which, bool val)
{u32 reg;switch (which) {case IRQCHIP_STATE_PENDING:reg = val ? GIC_DIST_PENDING_SET : GIC_DIST_PENDING_CLEAR;break;case IRQCHIP_STATE_ACTIVE:reg = val ? GIC_DIST_ACTIVE_SET : GIC_DIST_ACTIVE_CLEAR;break;case IRQCHIP_STATE_MASKED:reg = val ? GIC_DIST_ENABLE_CLEAR : GIC_DIST_ENABLE_SET;break;default:return -EINVAL;}gic_poke_irq(d, reg);return 0;
}static int gic_irq_get_irqchip_state(struct irq_data *d,enum irqchip_irq_state which, bool *val)
{switch (which) {case IRQCHIP_STATE_PENDING:*val = gic_peek_irq(d, GIC_DIST_PENDING_SET);break;case IRQCHIP_STATE_ACTIVE:*val = gic_peek_irq(d, GIC_DIST_ACTIVE_SET);break;case IRQCHIP_STATE_MASKED:*val = !gic_peek_irq(d, GIC_DIST_ENABLE_SET);break;default:return -EINVAL;}return 0;
}

irq_domain_alloc_irqs()调用__irq_domain_alloc_irqs()进行struct irq_desc、struct irq_data以及中断映射的处理。

这里的参数nr_irqs一般为1，每次只处理一个中断。

irq_domain_alloc_descs()->irq_alloc_descs()->__irq_alloc_descs()进行struct irq_desc的分配，返回的参数是Linux中断号。

int __irq_domain_alloc_irqs(struct irq_domain *domain, int irq_base,unsigned int nr_irqs, int node, void *arg,bool realloc)
{
...if (realloc && irq_base >= 0) {virq = irq_base;} else {virq = irq_domain_alloc_descs(irq_base, nr_irqs, 0, node);-------从allocated_irqs位图中查找第一个nr_irqs个空闲的比特位，最终调用__irq_alloc_descs。if (virq < 0) {pr_debug("cannot allocate IRQ(base %d, count %d)\n",irq_base, nr_irqs);return virq;}}if (irq_domain_alloc_irq_data(domain, virq, nr_irqs)) {--------------分配struct irq_data数据结构。pr_debug("cannot allocate memory for IRQ%d\n", virq);ret = -ENOMEM;goto out_free_desc;}mutex_lock(&irq_domain_mutex);ret = irq_domain_alloc_irqs_recursive(domain, virq, nr_irqs, arg);----调用struct irq_domain中的alloc回调函数进行硬件中断号和软件中断号的映射。if (ret < 0) {mutex_unlock(&irq_domain_mutex);goto out_free_irq_data;}for (i = 0; i < nr_irqs; i++)irq_domain_insert_irq(virq + i);mutex_unlock(&irq_domain_mutex);return virq;
...
}int __ref
__irq_alloc_descs(int irq, unsigned int from, unsigned int cnt, int node,struct module *owner)
{
...mutex_lock(&sparse_irq_lock);start = bitmap_find_next_zero_area(allocated_irqs, IRQ_BITMAP_BITS,from, cnt, 0);-------------------在allocated_irqs位图中查找第一个连续cnt个为0的比特位区域。
...bitmap_set(allocated_irqs, start, cnt);-------------bitmap_set()设置这些比特位，表示这些比特位已经被占用。mutex_unlock(&sparse_irq_lock);return alloc_descs(start, cnt, node, owner);--------这里要看是否定义了CONFIG_SPARSE_IRQ，如果定义了需要动态分配一个struct irq_desc数据结构，以Radix Tree方式存储；没有的话则从irq_desc全局变量中加上偏移即可。err:mutex_unlock(&sparse_irq_lock);return ret;
}

irq_domain_alloc_irqs_recursive()会根据实际情况决定中断控制器的递归处理，

static int irq_domain_alloc_irqs_recursive(struct irq_domain *domain,unsigned int irq_base,unsigned int nr_irqs, void *arg)
{int ret = 0;struct irq_domain *parent = domain->parent;bool recursive = irq_domain_is_auto_recursive(domain);BUG_ON(recursive && !parent);if (recursive)ret = irq_domain_alloc_irqs_recursive(parent, irq_base,nr_irqs, arg);if (ret >= 0)ret = domain->ops->alloc(domain, irq_base, nr_irqs, arg);if (ret < 0 && recursive)irq_domain_free_irqs_recursive(parent, irq_base, nr_irqs);return ret;
}

至此完成了中断DeviceTree的解析，各数据结构的初始化，以及最主要的硬件中断号到Linux中断号的映射。

3. ARM底层中断处理

ARM底层中断处理的范围是从中断异常触发，到irq_handler。

3.1 中断硬件行为

外设有事件需要报告SoC时，通过和SoC链接的中断管脚发送中断信号，可能是边沿触发信号也可能是电平触发信号。

中断控制器会感知中断信号，中断控制器仲裁单元选择优先级最高的中断发送到CPU Interface，CPU Interface决定将中断分发到哪个CPU核心。

GIC控制器和CPU核心之间通过一个nIRQ(IRQ request input line)信号来通知CPU。

CPU核心感知到中断发生之后，硬件会做如下工作：

保存中断发生时CPSR寄存器内容到SPSR_irq寄存器中
修改CPSR寄存器，让CPU进入处理器模式(processor mode)中的IRQ模式，即修改CPSR寄存器中的M域设置为IRQ Mode。
硬件自动关闭中断IRQ或FIQ，即CPSR中的IRQ位或FIQ位置1。------------硬件自动关中断
保存返回地址到LR_irq寄存器中。
硬件自动调转到中断向量表的IRQ向量。-------------------------------------------从此处开始进入软件领域

当从中断返回时需要软件实现如下操作：

从SPSR_irq寄存器中恢复数据到CPSR中。
从LR_irq中恢复内容到PC中，从而返回到中断点的下一个指令处执行。

3.2 中断异常向量

3.2.1 中断异常向量代码段初始化

内核编译时，异常向量表存放在可执行文件的__init段中：arch/arm/kernel/vmlinux.lds.S。

__vectors_start和__vectors_end指向vectors段的开始和结束地址，__stubs_start和__stubs_end存放异常向量stubs代码段。两者都是页面对齐，大小都为一个页面。

    __vectors_start = .;.vectors 0 : AT(__vectors_start) {*(.vectors)----------------------------------保存.vectors段数据}. = __vectors_start + SIZEOF(.vectors);__vectors_end = .;__stubs_start = .;.stubs 0x1000 : AT(__stubs_start) {*(.stubs)------------------------------------存放.stubs段数据}. = __stubs_start + SIZEOF(.stubs);__stubs_end = .;

系统初始化时会把上述两个段复制到高端地址处，即ixffff_0000：start_kernel->setup_arch->paging_init->devicemap_init。

static void __init devicemaps_init(const struct machine_desc *mdesc)
{struct map_desc map;unsigned long addr;void *vectors;/** Allocate the vector page early.*/vectors = early_alloc(PAGE_SIZE * 2);-------------------------------分配两个页面用于映射到high vectors高端地址。early_trap_init(vectors);-------------------------------------------实现异常向量表的复制动作。.../** Create a mapping for the machine vectors at the high-vectors* location (0xffff0000).  If we aren't using high-vectors, also* create a mapping at the low-vectors virtual address.*/map.pfn = __phys_to_pfn(virt_to_phys(vectors));---------------------vectors物理页面号map.virtual = 0xffff0000;-------------------------------------------待映射到的虚拟地址0xffff_0000~0xffff_0fffmap.length = PAGE_SIZE;---------------------------------------------映射区间大小
#ifdef CONFIG_KUSER_HELPERSmap.type = MT_HIGH_VECTORS;-----------------------------------------映射到high vector
#elsemap.type = MT_LOW_VECTORS;
#endifcreate_mapping(&map);if (!vectors_high()) {map.virtual = 0;map.length = PAGE_SIZE * 2;map.type = MT_LOW_VECTORS;create_mapping(&map);}/* Now create a kernel read-only mapping */map.pfn += 1;map.virtual = 0xffff0000 + PAGE_SIZE;------------------------------映射到0xffff_1000~0xffff_1ffffmap.length = PAGE_SIZE;map.type = MT_LOW_VECTORS;create_mapping(&map);
...
}

early_trap_init分别将__vectors_start和__stubs_start两个页面复制到分配的两个页面中。

void __init early_trap_init(void *vectors_base)
{
...unsigned long vectors = (unsigned long)vectors_base;extern char __stubs_start[], __stubs_end[];extern char __vectors_start[], __vectors_end[];unsigned i;vectors_page = vectors_base;/** Poison the vectors page with an undefined instruction.  This* instruction is chosen to be undefined for both ARM and Thumb* ISAs.  The Thumb version is an undefined instruction with a* branch back to the undefined instruction.*/for (i = 0; i < PAGE_SIZE / sizeof(u32); i++)((u32 *)vectors_base)[i] = 0xe7fddef1;---------------------------第一个页面全部填充未定义指令0xe7fddef1。/** Copy the vectors, stubs and kuser helpers (in entry-armv.S)* into the vector page, mapped at 0xffff0000, and ensure these* are visible to the instruction stream.*/memcpy((void *)vectors, __vectors_start, __vectors_end - __vectors_start);memcpy((void *)vectors + 0x1000, __stubs_start, __stubs_end - __stubs_start);
...
}

3.2.2 中断异常向量

中断发生后，软件跳转到中断向量表开始vector_irq执行，vector_irq在结尾的时候根据中断发生点所在模式，决定跳转到__irq_usr或者__irq_svc。

vector_irq在arch/arm/kernel/entry-armv.S由宏vector_stub定义。

关于correction==4，需要减去4字节才是返回地址？

vector_stub宏参数correction为4,。

正在执行指令A时发生了中断，由于ARM流水线和指令预取等原因，pc指向A+8B处，那么必须等待指令A执行完毕才能处理该中断，这时PC已经更新到A+12B处。

进入中断响应前夕，pc寄存器的内容被装入lr寄存器中，lr=pc-4，即A+8B地址处。

因此返回时要pc=lr-4，才是被中断时要执行的下一条指令。所以lr要回退4B。

    .section .vectors, "ax", %progbits
__vectors_start:W(b)    vector_rstW(b)    vector_undW(ldr)    pc, __vectors_start + 0x1000W(b)    vector_pabtW(b)    vector_dabtW(b)    vector_addrexcptnW(b)    vector_irq---------------------------------------------------------------跳转到vector_irqW(b)    vector_fiq/** Interrupt dispatcher*/vector_stub    irq, IRQ_MODE, 4------------------------------------------------vector_stub宏定义了vector_irq.long    __irq_usr            @  0  (USR_26 / USR_32).long    __irq_invalid            @  1  (FIQ_26 / FIQ_32).long    __irq_invalid            @  2  (IRQ_26 / IRQ_32).long    __irq_svc            @  3  (SVC_26 / SVC_32)----------------------------svc模式数值是0b10011，与上0xf后就是3。.long    __irq_invalid            @  4.long    __irq_invalid            @  5.long    __irq_invalid            @  6.long    __irq_invalid            @  7.long    __irq_invalid            @  8.long    __irq_invalid            @  9.long    __irq_invalid            @  a.long    __irq_invalid            @  b.long    __irq_invalid            @  c.long    __irq_invalid            @  d.long    __irq_invalid            @  e.long    __irq_invalid            @  f

3.3 内核空间中断处理__irq_svc

__irq_svc处理发生在内核空间的中断，主要svc_entry保护中断现场；irq_handler执行中断处理；如果打开抢占功能，检查是否可以抢占；最后svc_exit执行中断退出处理。

__irq_svc:svc_entryirq_handler#ifdef CONFIG_PREEMPT-----------------------------------------------------中断处理结束后，发生抢占的地方♥get_thread_info tskldr    r8, [tsk, #TI_PREEMPT]        @ get preempt count--------------获取thread_info->preempt_cpunt变量;preempt_count为0，说明可以抢占进程；preempt_count大于0，表示不能抢占。ldr    r0, [tsk, #TI_FLAGS]        @ get flags------------------------获取thread_info->flags变量teq    r8, #0                @ if preempt count != 0movne    r0, #0                @ force flags to 0tst    r0, #_TIF_NEED_RESCHED-----------------------------------------判断是否设置了_TIF_NEED_RESCHED标志位blne    svc_preempt
#endifsvc_exit r5, irq = 1            @ return from exceptionUNWIND(.fnend        )
ENDPROC(__irq_svc)

svc_entry将中断现场保存到内核栈中，主要是struct pt_regs中的寄存器。

    .macro    svc_entry, stack_hole=0, trace=1UNWIND(.fnstart        )UNWIND(.save {r0 - pc}        )sub    sp, sp, #(S_FRAME_SIZE + \stack_hole - 4)
#ifdef CONFIG_THUMB2_KERNELSPFIX(    str    r0, [sp]    )    @ temporarily savedSPFIX(    mov    r0, sp        )SPFIX(    tst    r0, #4        )    @ test original stack alignmentSPFIX(    ldr    r0, [sp]    )    @ restored
#elseSPFIX(    tst    sp, #4        )
#endifSPFIX(    subeq    sp, sp, #4    )stmia    sp, {r1 - r12}ldmia    r0, {r3 - r5}add    r7, sp, #S_SP - 4    @ here for interlock avoidancemov    r6, #-1            @  ""  ""      ""       ""add    r2, sp, #(S_FRAME_SIZE + \stack_hole - 4)SPFIX(    addeq    r2, r2, #4    )str    r3, [sp, #-4]!        @ save the "real" r0 copied@ from the exception stackmov    r3, lr@@ We are now ready to fill in the remaining blanks on the stack:@@  r2 - sp_svc@  r3 - lr_svc@  r4 - lr_<exception>, already fixed up for correct return/restart@  r5 - spsr_<exception>@  r6 - orig_r0 (see pt_regs definition in ptrace.h)@stmia    r7, {r2 - r6}.if \trace
#ifdef CONFIG_TRACE_IRQFLAGSbl    trace_hardirqs_off
#endif.endif.endm

svc_exit准备返回中断现场，然后通过ldmia指令从栈中恢复15个寄存器，包括pc内容，至此整个中断完成并返回。

    .macro    svc_exit, rpsr, irq = 0...msr    spsr_cxsf, \rpsrldmia    sp, {r0 - pc}^            @ load r0 - pc, cpsr.endm

irq_handler进入高层中断处理。

4. 高层中断处理

irq_handler汇编宏是ARCH层和高层中断处理分割线，在这里从汇编跳转到C进行GIC相关处理。

前面介绍了一个中断是如何从硬件中断号映射到Linux中断号的，那么当一个中断产生后它从应将到软件识别中断号，再到转换成Linux中断号是什么路径呢？

这里就从irq_handler开始分析流程：

irq_handler() ->handle_arch_irq()->gic_handle_irq() ->handle_domain_irq()->__handle_domain_irq()-------------读取IAR寄存器，响应中断，获取硬件中断号 ->irq_find_mapping()------------------------------------------------将硬件中断号转变成Linux中断号 ->generic_handle_irq()---------------------------------------------之后的操作都是Linux中断号 ->handle_percpu_devid_irq()-----------------------------------SGI/PPI类型中断处理 ->handle_fasteoi_irq()--------------------------------------------SPI类型中断处理 ->handle_irq_event()->handle_irq_event_percpu()------执行中断处理核心函数 ->action->handler-----------------------------------------------执行primary handler。 ->__irq_wake_thread()----------------------------------------根据需要唤醒中断内核线程

4.1 irq_handler

irq_handler宏调用handle_arch_irq函数，这个函数set_handle_irq注册，GICv2对应gic_handle_irq。

    .macro    irq_handler
#ifdef CONFIG_MULTI_IRQ_HANDLERldr    r1, =handle_arch_irqmov    r0, spadr    lr, BSYM(9997f)ldr    pc, [r1]
#elsearch_irq_handler_default
#endif
9997:.endm

4.2 gic_handle_irq

git_init_bases设置handle_arch_irq为gic_handle_irq。

void __init gic_init_bases(unsigned int gic_nr, int irq_start,void __iomem *dist_base, void __iomem *cpu_base,u32 percpu_offset, struct device_node *node)
{
...if (gic_nr == 0) {
...set_handle_irq(gic_handle_irq);}
...
}void __init set_handle_irq(void (*handle_irq)(struct pt_regs *))
{if (handle_arch_irq)return;handle_arch_irq = handle_irq;
}

gic_handle_irq对将中断分为两组：SGI、PPI/SPI。

SGI类型中断交给handle_IPI()处理；PPI/SPI类型交给handle_domain_irq处理。

static void __exception_irq_entry gic_handle_irq(struct pt_regs *regs)
{u32 irqstat, irqnr;struct gic_chip_data *gic = &gic_data[0];void __iomem *cpu_base = gic_data_cpu_base(gic);do {irqstat = readl_relaxed(cpu_base + GIC_CPU_INTACK);---读取IAR寄存器，表示响应中断。irqnr = irqstat & GICC_IAR_INT_ID_MASK;-----------------GICC_IAR_INT_ID_MASK为0x3ff，即低10位，所以中断最多从0~1023。if (likely(irqnr > 15 && irqnr < 1021)) {handle_domain_irq(gic->domain, irqnr, regs);continue;}if (irqnr < 16) {---------------------------------------SGI类型的中断是CPU核间通信所用，只有定义了CONFIG_SMP才有意义。writel_relaxed(irqstat, cpu_base + GIC_CPU_EOI);----直接写EOI寄存器，表示结束中断。
#ifdef CONFIG_SMPhandle_IPI(irqnr, regs);----------------------------irqnr表示SGI中断类型
#endifcontinue;}break;} while (1);
}

handle_domain_irq调用__handle_domain_irq，其中lookup置为true。

irq_enter显式告诉Linux内核现在要进入中断上下文了，在处理完中断后调用irq_exit告诉Linux已经完成中断处理过程。

int __handle_domain_irq(struct irq_domain *domain, unsigned int hwirq,bool lookup, struct pt_regs *regs)
{struct pt_regs *old_regs = set_irq_regs(regs);unsigned int irq = hwirq;int ret = 0;irq_enter();-----------------------------------------------通过显式增加hardirq域计数，通知Linux进入中断上下文#ifdef CONFIG_IRQ_DOMAINif (lookup)irq = irq_find_mapping(domain, hwirq);-----------------根据硬件中断号找到对应的软件中断号
#endif/** Some hardware gives randomly wrong interrupts.  Rather* than crashing, do something sensible.*/if (unlikely(!irq || irq >= nr_irqs)) {ack_bad_irq(irq);ret = -EINVAL;} else {generic_handle_irq(irq);--------------------------------开始具体某一个中断的处理，此处irq已经是Linux中断号。}irq_exit();-------------------------------------------------退出中断上下文set_irq_regs(old_regs);return ret;
}

irq_find_mapping在struct irq_domain中根据hwirq找到Linux环境的irq。

unsigned int irq_find_mapping(struct irq_domain *domain,irq_hw_number_t hwirq)
{struct irq_data *data;
.../* Check if the hwirq is in the linear revmap. */if (hwirq < domain->revmap_size)return domain->linear_revmap[hwirq];----------------linear_revmap[]在__irq_domain_alloc_irqs()->irq_domain_insert_irq()时赋值。
...
}

generic_handle_irq参数是irq号，irq_to_desc()根据irq号找到对应的struct irq_desc。

然后调用irq_desc->handle_irq处理对应的中断。

int generic_handle_irq(unsigned int irq)
{struct irq_desc *desc = irq_to_desc(irq);if (!desc)return -EINVAL;generic_handle_irq_desc(irq, desc);return 0;
}static inline void generic_handle_irq_desc(unsigned int irq, struct irq_desc *desc)
{desc->handle_irq(irq, desc);
}

关于desc->handle_irq来历，在每个中断注册的时候，由gic_irq_domain_map根据hwirq号决定。

在gic_irq_domain_map的时候根据hw号决定handle，hw硬件中断号小于32指向handle_percpu_devid_irq，其他情况指向handle_fasteoi_irq。

void
__irq_set_handler(unsigned int irq, irq_flow_handler_t handle, int is_chained,const char *name)
{
...desc->handle_irq = handle;desc->name = name;
...
}

handle_percpu_devid_irq处理0~31的SGI/PPI类型中断，首先响应IAR，然后执行handler，最后发送EOI。

void handle_percpu_devid_irq(unsigned int irq, struct irq_desc *desc)
{struct irq_chip *chip = irq_desc_get_chip(desc);struct irqaction *action = desc->action;void *dev_id = raw_cpu_ptr(action->percpu_dev_id);irqreturn_t res;kstat_incr_irqs_this_cpu(irq, desc);if (chip->irq_ack)chip->irq_ack(&desc->irq_data);trace_irq_handler_entry(irq, action);res = action->handler(irq, dev_id);trace_irq_handler_exit(irq, action, res);if (chip->irq_eoi)chip->irq_eoi(&desc->irq_data);-------------------调用gic_eoi_irq()函数
}

irq_enter和irq_exit显式地处理hardirq域计数，两者之间的部分属于中断上下文。

/** Enter an interrupt context.*/
void irq_enter(void)
{rcu_irq_enter();if (is_idle_task(current) && !in_interrupt()) {/** Prevent raise_softirq from needlessly waking up ksoftirqd* here, as softirq will be serviced on return from interrupt.*/local_bh_disable();tick_irq_enter();_local_bh_enable();}__irq_enter();---------------------------------------------显式增加hardirq域计数
}#define __irq_enter()                    \do {                        \account_irq_enter_time(current);    \preempt_count_add(HARDIRQ_OFFSET);    \----------------显式增加hardirq域计数trace_hardirq_enter();            \} while (0)void irq_exit(void)
{
#ifndef __ARCH_IRQ_EXIT_IRQS_DISABLEDlocal_irq_disable();
#elseWARN_ON_ONCE(!irqs_disabled());
#endifaccount_irq_exit_time(current);preempt_count_sub(HARDIRQ_OFFSET);---------------------------显式减少hardirq域计数if (!in_interrupt() && local_softirq_pending())--------------当前不处于中断上下文，且有pending的softirq，进行softirq处理。invoke_softirq();tick_irq_exit();rcu_irq_exit();trace_hardirq_exit(); /* must be last! */
}

4.2.1 中断上下文

判断当前进程是处于中断上下文，还是进程上下文依赖于preempt_count，这个变量在struct thread_info中。

preempt_count计数共32bit，从低到高依次是：

#define PREEMPT_BITS   8
#define SOFTIRQ_BITS    8
#define HARDIRQ_BITS    4
#define NMI_BITS    1

#define hardirq_count()    (preempt_count() & HARDIRQ_MASK)-----------------硬件中断计数
#define softirq_count()    (preempt_count() & SOFTIRQ_MASK)-----------------软中断计数
#define irq_count()    (preempt_count() & (HARDIRQ_MASK | SOFTIRQ_MASK \----包括NMI、硬中断、软中断三者计数| NMI_MASK))/** Are we doing bottom half or hardware interrupt processing?** in_irq()       - We're in (hard) IRQ context* in_softirq()   - We have BH disabled, or are processing softirqs* in_interrupt() - We're in NMI,IRQ,SoftIRQ context or have BH disabled* in_serving_softirq() - We're in softirq context* in_nmi()       - We're in NMI context* in_task()      - We're in task context** Note: due to the BH disabled confusion: in_softirq(),in_interrupt() really*       should not be used in new code.*/
#define in_irq()        (hardirq_count())----------------------------判断是否正在硬件中断上下文
#define in_softirq()        (softirq_count())------------------------判断是否正在处理软中断或者禁止BH。
#define in_interrupt()        (irq_count())--------------------------判断是否处于NMI、硬中断、软中断三者之一或者兼有上下文
#define in_serving_softirq()    (softirq_count() & SOFTIRQ_OFFSET)---判断是否处于软中断上下文。
#define in_nmi()        (preempt_count() & NMI_MASK)-----------------判断是否处于NMI上下文
#define in_task()        (!(preempt_count() & \(NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET)))------判断是否处于进程上下文

思考：in_softirq()和in_serving_softirq()区别？in_interrupt()和in_task()中关于SOFTIRQ_MASK和SOFTIRQ_OFFSET区别？

4.3 handle_fasteoi_irq

handle_fsteoi_irq处理SPI类型的中断，将主要工作交给handle_irq_event()。

handle_irq_event_percpu()首先处理action->handler，有需要则唤醒中断内核线程，执行action->thread_fn。

void
handle_fasteoi_irq(unsigned int irq, struct irq_desc *desc)
{struct irq_chip *chip = desc->irq_data.chip;raw_spin_lock(&desc->lock);if (!irq_may_run(desc))goto out;desc->istate &= ~(IRQS_REPLAY | IRQS_WAITING);kstat_incr_irqs_this_cpu(irq, desc);/** If its disabled or no action available* then mask it and get out of here:*/if (unlikely(!desc->action || irqd_irq_disabled(&desc->irq_data))) {---如果该中断没有指定action描述符或该中断被关闭了IRQD_IRQ_DISABLED，设置该中断状态为IRQS_PENDING，且mask_irq()屏蔽该中断。desc->istate |= IRQS_PENDING;mask_irq(desc);goto out;}if (desc->istate & IRQS_ONESHOT)----------------------------------------如果中断是IRQS_ONESHOT，不支持中断嵌套，那么应该调用mask_irq()来屏蔽该中断源。mask_irq(desc);preflow_handler(desc);--------------------------------------------------取决于是否定义了freflow_handler()handle_irq_event(desc);cond_unmask_eoi_irq(desc, chip);----------------------------------------根据不同条件执行unmask_irq()解除中断屏蔽，或者执行irq_chip->irq_eoi发送EOI信号，通知GIC中断处理完毕。raw_spin_unlock(&desc->lock);return;
out:if (!(chip->flags & IRQCHIP_EOI_IF_HANDLED))chip->irq_eoi(&desc->irq_data);raw_spin_unlock(&desc->lock);
}

handle_irq_event调用handle_irq_event_percpu，执行action->handler()，如有需要唤醒内核中断线程执行action->thread_fn。

irqreturn_t handle_irq_event(struct irq_desc *desc)
{struct irqaction *action = desc->action;irqreturn_t ret;desc->istate &= ~IRQS_PENDING;--------------------------清除IRQS_PENDING标志位irqd_set(&desc->irq_data, IRQD_IRQ_INPROGRESS);---------设置IRQD_IRQ_INPROGRESS标志位，表示正在处理硬件中断。raw_spin_unlock(&desc->lock);ret = handle_irq_event_percpu(desc, action);raw_spin_lock(&desc->lock);irqd_clear(&desc->irq_data, IRQD_IRQ_INPROGRESS);-------清除IRQD_IRQ_INPROGRESS标志位，表示中断处理结束。return ret;
}irqreturn_t
handle_irq_event_percpu(struct irq_desc *desc, struct irqaction *action)
{irqreturn_t retval = IRQ_NONE;unsigned int flags = 0, irq = desc->irq_data.irq;do {----------------------------------------------------遍历中断描述符中的action链表，依次执行每个action元素中的primary handler回调函数action->handler。irqreturn_t res;trace_irq_handler_entry(irq, action);res = action->handler(irq, action->dev_id);---------执行struct irqaction的handler函数。trace_irq_handler_exit(irq, action, res);if (WARN_ONCE(!irqs_disabled(),"irq %u handler %pF enabled interrupts\n",irq, action->handler))local_irq_disable();---------------------------switch (res) {case IRQ_WAKE_THREAD:-------------------------------去唤醒内核中断线程/** Catch drivers which return WAKE_THREAD but* did not set up a thread function*/if (unlikely(!action->thread_fn)) {warn_no_thread(irq, action);----------------输出一个打印表示没有中断处理函数break;}__irq_wake_thread(desc, action);----------------唤醒此中断对应的内核线程/* Fall through to add to randomness */case IRQ_HANDLED:-----------------------------------已经处理完毕，可以结束。flags |= action->flags;break;default:break;}retval |= res;action = action->next;} while (action);add_interrupt_randomness(irq, flags);if (!noirqdebug)note_interrupt(irq, desc, retval);return retval;
}

4.3.1 唤醒中断内核线程

__irq_wake_thread唤醒对应中断的内核线程。

void __irq_wake_thread(struct irq_desc *desc, struct irqaction *action)
{/** In case the thread crashed and was killed we just pretend that* we handled the interrupt. The hardirq handler has disabled the* device interrupt, so no irq storm is lurking.*/if (action->thread->flags & PF_EXITING)return;/** Wake up the handler thread for this action. If the* RUNTHREAD bit is already set, nothing to do.*/if (test_and_set_bit(IRQTF_RUNTHREAD, &action->thread_flags))--------------若已经对IRQF_RUNTHREAD置位，表示已经处于唤醒中，该函数直接返回。return;desc->threads_oneshot |= action->thread_mask;--------------------thread_mask在共享中断中，每一个action有一个比特位来表示。thread_oneshot每个比特位表示正在处理的共享oneshot类型中断的中断线程。atomic_inc(&desc->threads_active);-------------------------------活跃中断线程计数wake_up_process(action->thread);---------------------------------唤醒action的thread内核线程
}

4.3.2 创建内核中断线程

irq_thread在中断注册的时候，如果条件满足同时创建rq/xx-xx内核中断线程，线程优先级是49(99-50)，调度策略是SCHED_FIFO。

static int
__setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new)
{
.../** Create a handler thread when a thread function is supplied* and the interrupt does not nest into another interrupt* thread.*/if (new->thread_fn && !nested) {struct task_struct *t;static const struct sched_param param = {.sched_priority = MAX_USER_RT_PRIO/2,-------------------------------设置irq内核线程的优先级，在/proc/xxx/sched中看到的prio为MAX_RT_PRIO-1-sched_priority。};t = kthread_create(irq_thread, new, "irq/%d-%s", irq,new->name);--------------------------------------------------创建线程名为irq/xxx-xxx的内核线程，线程执行函数是irq_thread。
...sched_setscheduler_nocheck(t, SCHED_FIFO, &param);----------------------设置进程调度策略为SCHED_FIFO。/** We keep the reference to the task struct even if* the thread dies to avoid that the interrupt code* references an already freed task_struct.*/get_task_struct(t);new->thread = t;-------------------------------------------------------将当前线程和irq_action关联起来set_bit(IRQTF_AFFINITY, &new->thread_flags);--------------------------对中断线程设置CPU亲和性}
...
}

4.3.3 内核中断线程执行

irq_thread是中断线程的执行函数，在irq_wait_for_interrupt()中等待。

irq_wait_for_interrupt()中判断IRQTF_RUNTHREAD标志位，没有置位则schedule()换出CPU，进行睡眠。

直到__irq_wake_thread()置位了IRQTF_RUNTHREAD，并且wake_up_process()后，irq_wait_for_interrupt()返回0。

static int irq_thread(void *data)
{struct callback_head on_exit_work;struct irqaction *action = data;struct irq_desc *desc = irq_to_desc(action->irq);irqreturn_t (*handler_fn)(struct irq_desc *desc,struct irqaction *action);if (force_irqthreads && test_bit(IRQTF_FORCED_THREAD,&action->thread_flags))handler_fn = irq_forced_thread_fn;elsehandler_fn = irq_thread_fn;init_task_work(&on_exit_work, irq_thread_dtor);task_work_add(current, &on_exit_work, false);irq_thread_check_affinity(desc, action);while (!irq_wait_for_interrupt(action)) {irqreturn_t action_ret;irq_thread_check_affinity(desc, action);action_ret = handler_fn(desc, action);-----------执行中断内核线程函数if (action_ret == IRQ_HANDLED)atomic_inc(&desc->threads_handled);----------增加threads_handled计数wake_threads_waitq(desc);------------------------唤醒wait_for_threads等待队列}/** This is the regular exit path. __free_irq() is stopping the* thread via kthread_stop() after calling* synchronize_irq(). So neither IRQTF_RUNTHREAD nor the* oneshot mask bit can be set. We cannot verify that as we* cannot touch the oneshot mask at this point anymore as* __setup_irq() might have given out currents thread_mask* again.*/task_work_cancel(current, irq_thread_dtor);return 0;
}static int irq_wait_for_interrupt(struct irqaction *action)
{set_current_state(TASK_INTERRUPTIBLE);while (!kthread_should_stop()) {if (test_and_clear_bit(IRQTF_RUNTHREAD,&action->thread_flags)) {------------判断thread_flags是否设置IRQTF_RUNTHREAD标志位，如果设置则设置当前状态TASK_RUNNING并返回0。此处和__irq_wake_thread中设置IRQTF_RUNTHREAD对应。__set_current_state(TASK_RUNNING);return 0;}schedule();-----------------------------------------换出CPU，在此等待睡眠set_current_state(TASK_INTERRUPTIBLE);}__set_current_state(TASK_RUNNING);return -1;
}static irqreturn_t irq_thread_fn(struct irq_desc *desc,struct irqaction *action)
{irqreturn_t ret;ret = action->thread_fn(action->irq, action->dev_id);---执行中断内核线程函数，为request_threaded_irq注册中断参数thread_fn。irq_finalize_oneshot(desc, action);---------------------针对oneshot类型中断收尾处理，主要是去屏蔽中断。return ret;
}

irq_finalize_oneshot()对ontshot类型的中断进行收尾操作。

static void irq_finalize_oneshot(struct irq_desc *desc,struct irqaction *action)
{if (!(desc->istate & IRQS_ONESHOT) ||action->handler == irq_forced_secondary_handler)return;
again:chip_bus_lock(desc);raw_spin_lock_irq(&desc->lock);/** Implausible though it may be we need to protect us against* the following scenario:** The thread is faster done than the hard interrupt handler* on the other CPU. If we unmask the irq line then the* interrupt can come in again and masks the line, leaves due* to IRQS_INPROGRESS and the irq line is masked forever.** This also serializes the state of shared oneshot handlers* versus "desc->threads_onehsot |= action->thread_mask;" in* irq_wake_thread(). See the comment there which explains the* serialization.*/if (unlikely(irqd_irq_inprogress(&desc->irq_data))) {-----------必须等待硬件中断处理程序清除IRQD_IRQ_INPROGRESS标志位，见handle_irq_event()。因为该标志位表示硬件中断处理程序正在处理硬件中断，直到硬件中断处理完毕才会清除该标志。raw_spin_unlock_irq(&desc->lock);chip_bus_sync_unlock(desc);cpu_relax();goto again;}/** Now check again, whether the thread should run. Otherwise* we would clear the threads_oneshot bit of this thread which* was just set.*/if (test_bit(IRQTF_RUNTHREAD, &action->thread_flags))goto out_unlock;desc->threads_oneshot &= ~action->thread_mask;if (!desc->threads_oneshot && !irqd_irq_disabled(&desc->irq_data) &&irqd_irq_masked(&desc->irq_data))unmask_threaded_irq(desc);----------------------------------执行EOI或者去中断屏蔽。out_unlock:raw_spin_unlock_irq(&desc->lock);chip_bus_sync_unlock(desc);
}

至此一个中断的执行完毕。

4.4 如何保证IRQS_ONESHOT不嵌套？

5. 注册中断

5.1 中断、线程、中断线程化

中断处理程序包括上半部硬件中断处理程序，下半部处理机制，包括软中断、tasklet、workqueue、中断线程化。

当一个外设中断发生后，内核会执行一个函数来响应该中断，这个函数通常被称为中断处理程序或中断服务例程。

上半部硬件中断处理运行在中断上下文中，要求快速完成并且退出中断。

中断线程化是实时Linux项目开发的一个新特性，目的是降低中断处理对系统实时延迟的影响。

在LInux内核里，中断具有最高优先级，只要有中断发生，内核会暂停手头的工作转向中断处理，等到所有挂起等待的中断和软终端处理完毕后才会执行进程调度，因此这个过程会造成实时任务得不到及时处理。

中断上下文总是抢占进程上下文，中断上下文不仅是中断处理程序，还包括softirq、tasklet等，中断上下文成了优化Linux实时性的最大挑战之一。

5.2 中断注册接口

IRQF_*描述的中断标志位用于request_threaded_irq()申请中断时描述该中断的特性。

IRQS_*的中断标志位是位于struct irq_desc数据结构的istate成员，也即core_internal_state__do_not_mess_with_it。

IRQD_*是struct irq_data数据结构中的state_use_accessors成员一组中断标志位，通常用于描述底层中断状态。

关于IRQF_ONESHOT特别解释：必须在硬件中断处理结束之后才能重新使能中断；线程化中断处理过程中保持中断线处于关闭状态，直到该中断线上所有thread_fn执行完毕。

#define IRQF_TRIGGER_NONE    0x00000000
#define IRQF_TRIGGER_RISING    0x00000001---------------------------上升沿触发
#define IRQF_TRIGGER_FALLING    0x00000002--------------------------下降沿触发
#define IRQF_TRIGGER_HIGH    0x00000004-----------------------------高电平触发
#define IRQF_TRIGGER_LOW    0x00000008------------------------------地电平触发
#define IRQF_TRIGGER_MASK    (IRQF_TRIGGER_HIGH | IRQF_TRIGGER_LOW | \IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING)--------四种触发类型
#define IRQF_TRIGGER_PROBE    0x00000010#define IRQF_SHARED        0x00000080-------------------------------多个设备共享一个中断号
#define IRQF_PROBE_SHARED    0x00000100-----------------------------中断处理程序允许sharing mismatch发生
#define __IRQF_TIMER        0x00000200------------------------------标记一个时钟中断
#define IRQF_PERCPU        0x00000400-------------------------------属于某个特定CPU的中断
#define IRQF_NOBALANCING    0x00000800------------------------------禁止在多CPU之间做中断均衡
#define IRQF_IRQPOLL        0x00001000------------------------------中断被用作轮询
#define IRQF_ONESHOT        0x00002000------------------------------一次性触发中断，不允许嵌套。
#define IRQF_NO_SUSPEND        0x00004000---------------------------在系统睡眠过程中不要关闭该中断
#define IRQF_FORCE_RESUME    0x00008000-----------------------------在系统唤醒过程中必须抢孩子打开该中断
#define IRQF_NO_THREAD        0x00010000----------------------------表示该中断不会给线程化
#define IRQF_EARLY_RESUME    0x00020000
#define IRQF_COND_SUSPEND    0x00040000#define IRQF_TIMER        (__IRQF_TIMER | IRQF_NO_SUSPEND | IRQF_NO_THREAD)enum {IRQS_AUTODETECT        = 0x00000001,-------------------处于自动侦测状态IRQS_SPURIOUS_DISABLED    = 0x00000002,----------------被视为“伪中断”并被禁用IRQS_POLL_INPROGRESS    = 0x00000008,------------------正处于轮询调用actionIRQS_ONESHOT        = 0x00000020,----------------------表示只执行一次，由IRQF_ONESHOT转换而来，在中断线程化执行完成后需要小心对待，见irq_finalize_oneshot()。IRQS_REPLAY        = 0x00000040,-----------------------重新发送一次中断IRQS_WAITING        = 0x00000080,----------------------处于等待状态IRQS_PENDING        = 0x00000200,----------------------该中断被挂起IRQS_SUSPENDED        = 0x00000800,--------------------该中断被暂停
};enum {IRQD_TRIGGER_MASK        = 0xf,-------------------------该中断触发类型IRQD_SETAFFINITY_PENDING    = (1 <<  8),IRQD_NO_BALANCING        = (1 << 10),IRQD_PER_CPU            = (1 << 11),IRQD_AFFINITY_SET        = (1 << 12),IRQD_LEVEL            = (1 << 13),IRQD_WAKEUP_STATE        = (1 << 14),IRQD_MOVE_PCNTXT        = (1 << 15),IRQD_IRQ_DISABLED        = (1 << 16),--------------------该中断处于关闭状态IRQD_IRQ_MASKED            = (1 << 17),------------------该中断被屏蔽中IRQD_IRQ_INPROGRESS        = (1 << 18),------------------该中断正在被处理中IRQD_WAKEUP_ARMED        = (1 << 19),IRQD_FORWARDED_TO_VCPU        = (1 << 20),
};

struct irqaction是每个中断的irqaction描述符。

struct irqaction {irq_handler_t        handler;-----------primary handler函数指针void            *dev_id;----------------传递给中断处理程序的参数void __percpu        *percpu_dev_id;struct irqaction    *next;irq_handler_t        thread_fn;---------中断线程处理程序的函数指针struct task_struct    *thread;----------中断线程的task_struct数据结构unsigned int        irq;----------------Linux软件中断号unsigned int        flags;--------------注册中断时用的中断标志位，IRQF_*。unsigned long        thread_flags;------中断线程相关标志位unsigned long        thread_mask;-------在共享中断中，每一个action有一个比特位来表示。const char        *name;----------------中断线程名称struct proc_dir_entry    *dir;
} ____cacheline_internodealigned_in_smp;

request_irq调用request_threaded_irq进行中断注册，只是少了一个thread_fn参数。这也是两则的区别所在，request_irq不能注册线程化中断。

irq：Linux软件中断号，不是硬件中断号。

handler：指primary handler，也即request_irq的中断处理函数handler。

thread_fn：中断线程化的处理函数。

irqflags：中断标志位，见IRQF_*解释。

devname：中断名称。

dev_id：传递给中断处理程序的参数。

handler和thread_fn分别被赋给action->handler和action->thread_fn，组合如下：

	handler	thread_fn
1	√	√	先执行handler，然后条件执行thread_fn。
2	√	×	等同于request_irq()
3	×	√	handler=irq_default_primary_handler
4	×	×	返回-EINVAL

很多request_threaded_irq()使用第3种组合，irq_default_primary_handler()返回IRQ_WAKE_THREAD，将工作交给thread_fn进行处理。

第2种组合相当于request_irq()。

第4种组合不被允许，因为中断得不到任何处理。

第1种组合较复杂，在handler根据实际情况返回IRQ_WAKE_THREAD(唤醒内核中断线程)或者IRQ_HANDLED(中断已经处理完毕，不需要唤醒中断内核线程)。

request_threaded_irq()对参数进行检查之后，分配struct irqaction并填充，然后将注册工作交给__setup_irq()。

static inline int __must_check
request_irq(unsigned int irq, irq_handler_t handler, unsigned long flags,const char *name, void *dev)
{return request_threaded_irq(irq, handler, NULL, flags, name, dev);
}int request_threaded_irq(unsigned int irq, irq_handler_t handler,irq_handler_t thread_fn, unsigned long irqflags,const char *devname, void *dev_id)
{
...if (((irqflags & IRQF_SHARED) && !dev_id) ||-----------------------------共享中断设备必须传递啊dev_id参数来区分是哪个共享外设的中断(!(irqflags & IRQF_SHARED) && (irqflags & IRQF_COND_SUSPEND)) ||((irqflags & IRQF_NO_SUSPEND) && (irqflags & IRQF_COND_SUSPEND)))return -EINVAL;desc = irq_to_desc(irq);--------------------------------------------------通过Linux中断号找到对应中断描述符struct irq_desc。if (!desc)return -EINVAL;
...if (!handler) {if (!thread_fn)return -EINVAL;---------------------------------------------------handler和thread_fn不能同时为NULLhandler = irq_default_primary_handler;--------------------------------没有设置handler，irq_default_primary_handler()默认返回IRQ_WAKE_THREAD。}action = kzalloc(sizeof(struct irqaction), GFP_KERNEL);-------------------分配struct irqaction，并填充相应成员if (!action)return -ENOMEM;action->handler = handler;action->thread_fn = thread_fn;action->flags = irqflags;action->name = devname;action->dev_id = dev_id;chip_bus_lock(desc);-------------------------------------------------------调用desc->irq_data.chip->irq_bus_lock()进行加锁保护retval = __setup_irq(irq, desc, action);chip_bus_sync_unlock(desc);if (retval)kfree(action);
...return retval;
}

5.3 __setup_irq

一张图

__setup_irq()首先做参数检查，然后根据需要创建中断内核线程，这期间处理中断嵌套、oneshot、中断共享等问题。

还设置了中断触发类型设置，中断使能等工作。最后根据需要唤醒中断内核线程，并创建此中断相关sysfs节点。

/** Internal function to register an irqaction - typically used to* allocate special interrupts that are part of the architecture.*/
static int
__setup_irq(unsigned int irq, struct irq_desc *desc, struct irqaction *new)
{struct irqaction *old, **old_ptr;unsigned long flags, thread_mask = 0;int ret, nested, shared = 0;cpumask_var_t mask;if (!desc)return -EINVAL;if (desc->irq_data.chip == &no_irq_chip)----------------------表示没有正确初始化中断控制器，对于GICv2在gic_irq_domain_alloc()中指定chip为gic_chip。return -ENOSYS;if (!try_module_get(desc->owner))return -ENODEV;/** Check whether the interrupt nests into another interrupt* thread.*/nested = irq_settings_is_nested_thread(desc);-----------------对于设置了_IRQ_NESTED_THREAD嵌套类型的中断描述符，必须指定thread_fn。if (nested) {if (!new->thread_fn) {ret = -EINVAL;goto out_mput;}/** Replace the primary handler which was provided from* the driver for non nested interrupt handling by the* dummy function which warns when called.*/new->handler = irq_nested_primary_handler;} else {if (irq_settings_can_thread(desc))-----------------------判断该中断是否可以被线程化，如果没有设置_IRQ_NOTHREAD表示可以被强制线程化。irq_setup_forced_threading(new);}/** Create a handler thread when a thread function is supplied* and the interrupt does not nest into another interrupt* thread.*/if (new->thread_fn && !nested) {-----------------------------对不支持嵌套的线程化中断创建一个内核线程，实时SCHED_FIFO，优先级为50的实时线程。struct task_struct *t;static const struct sched_param param = {.sched_priority = MAX_USER_RT_PRIO/2,};t = kthread_create(irq_thread, new, "irq/%d-%s", irq,new->name);-----------------------------------由irq、中断号、中断名组成的中断线程名，处理函数是irq_thread()。if (IS_ERR(t)) {ret = PTR_ERR(t);goto out_mput;}sched_setscheduler_nocheck(t, SCHED_FIFO, &param);get_task_struct(t);new->thread = t;set_bit(IRQTF_AFFINITY, &new->thread_flags);}if (!alloc_cpumask_var(&mask, GFP_KERNEL)) {ret = -ENOMEM;goto out_thread;}/** Drivers are often written to work w/o knowledge about the* underlying irq chip implementation, so a request for a* threaded irq without a primary hard irq context handler* requires the ONESHOT flag to be set. Some irq chips like* MSI based interrupts are per se one shot safe. Check the* chip flags, so we can avoid the unmask dance at the end of* the threaded handler for those.*/if (desc->irq_data.chip->flags & IRQCHIP_ONESHOT_SAFE)----------表示该中断控制器不支持中断嵌套，所以flags去掉IRQF_ONESHOT。new->flags &= ~IRQF_ONESHOT;raw_spin_lock_irqsave(&desc->lock, flags);old_ptr = &desc->action;old = *old_ptr;if (old) {-----------------------------------------------------old指向desc->action指向的链表，old不为空说明已经有中断添加到中断描述符irq_desc中，说明这是一个共享中断。shared=1。
.../* add new interrupt at end of irq queue */do {/** Or all existing action->thread_mask bits,* so we can find the next zero bit for this* new action.*/thread_mask |= old->thread_mask;old_ptr = &old->next;old = *old_ptr;} while (old);shared = 1;}/** Setup the thread mask for this irqaction for ONESHOT. For* !ONESHOT irqs the thread mask is 0 so we can avoid a* conditional in irq_wake_thread().*/if (new->flags & IRQF_ONESHOT) {/** Unlikely to have 32 resp 64 irqs sharing one line,* but who knows.*/if (thread_mask == ~0UL) {ret = -EBUSY;goto out_mask;}new->thread_mask = 1 << ffz(thread_mask);} else if (new->handler == irq_default_primary_handler &&---------非IRQF_ONESHOT类型中断，且handler使用默认irq_default_primary_handler(),如果中断触发类型是LEVEL，如果中断出发后不清中断容易引发中断风暴。提醒驱动开发者，没有primary handler且中断控制器不支持硬件oneshot，必须显式指定IRQF_ONESHOT表示位。!(desc->irq_data.chip->flags & IRQCHIP_ONESHOT_SAFE)) {pr_err("Threaded irq requested with handler=NULL and !ONESHOT for irq %d\n",irq);ret = -EINVAL;goto out_mask;}if (!shared) {-------------------------------------------------非共享中断情况ret = irq_request_resources(desc);if (ret) {pr_err("Failed to request resources for %s (irq %d) on irqchip %s\n",new->name, irq, desc->irq_data.chip->name);goto out_mask;}init_waitqueue_head(&desc->wait_for_threads);/* Setup the type (level, edge polarity) if configured: */if (new->flags & IRQF_TRIGGER_MASK) {ret = __irq_set_trigger(desc, irq,-------------------调用gic_chip->irq_set_type设置中断触发类型。new->flags & IRQF_TRIGGER_MASK);if (ret)goto out_mask;}desc->istate &= ~(IRQS_AUTODETECT | IRQS_SPURIOUS_DISABLED | \IRQS_ONESHOT | IRQS_WAITING);irqd_clear(&desc->irq_data, IRQD_IRQ_INPROGRESS);---------清IRQD_IRQ_INPROGRESS标志位if (new->flags & IRQF_PERCPU) {irqd_set(&desc->irq_data, IRQD_PER_CPU);irq_settings_set_per_cpu(desc);}if (new->flags & IRQF_ONESHOT)desc->istate |= IRQS_ONESHOT;if (irq_settings_can_autoenable(desc))irq_startup(desc, true);else/* Undo nested disables: */desc->depth = 1;/* Exclude IRQ from balancing if requested */if (new->flags & IRQF_NOBALANCING) {irq_settings_set_no_balancing(desc);irqd_set(&desc->irq_data, IRQD_NO_BALANCING);}/* Set default affinity mask once everything is setup */setup_affinity(irq, desc, mask);} else if (new->flags & IRQF_TRIGGER_MASK) {
..}new->irq = irq;*old_ptr = new;irq_pm_install_action(desc, new);/* Reset broken irq detection when installing new handler */desc->irq_count = 0;desc->irqs_unhandled = 0;/** Check whether we disabled the irq via the spurious handler* before. Reenable it and give it another chance.*/if (shared && (desc->istate & IRQS_SPURIOUS_DISABLED)) {desc->istate &= ~IRQS_SPURIOUS_DISABLED;__enable_irq(desc, irq);}raw_spin_unlock_irqrestore(&desc->lock, flags);/** Strictly no need to wake it up, but hung_task complains* when no hard interrupt wakes the thread up.*/if (new->thread)wake_up_process(new->thread);------------------------------如果该中断被线程化，那么就唤醒该内核线程。这里每个中断对应一个线程。register_irq_proc(irq, desc);----------------------------------创建/proc/irq/xxx/目录及其节点。new->dir = NULL;register_handler_proc(irq, new);-------------------------------以action->name创建目录free_cpumask_var(mask);return 0;
...
}

irq_setup_forced_threading()判断是否强制当前中断线程化，然后对thread_flags置位IRQTF_FORCED_THREAD表示此中断被强制线程化。

将原来的primary handler弄到中断线程中去执行，原来的primary handler换成irq_default_primary_handler。

并设置secondary的primary handler指向irq_forced_secondary_handler()，原来的thread_fn移到secondary的中线程中执行。

static int irq_setup_forced_threading(struct irqaction *new)
{if (!force_irqthreads)---------------------------------------------如果内核启动参数包含threadirqs，则支持强制线程化。或者CONFIG_PREEMPT_RT_BASE实时补丁打开，这里也强制线程化。return 0;if (new->flags & (IRQF_NO_THREAD | IRQF_PERCPU | IRQF_ONESHOT))----和线程化矛盾的标志位。return 0;new->flags |= IRQF_ONESHOT;----------------------------------------强制线程化的中断都置位IRQF_ONESHOT。if (new->handler != irq_default_primary_handler && new->thread_fn) {/* Allocate the secondary action */new->secondary = kzalloc(sizeof(struct irqaction), GFP_KERNEL);if (!new->secondary)return -ENOMEM;new->secondary->handler = irq_forced_secondary_handler;new->secondary->thread_fn = new->thread_fn;new->secondary->dev_id = new->dev_id;new->secondary->irq = new->irq;new->secondary->name = new->name;}/* Deal with the primary handler */set_bit(IRQTF_FORCED_THREAD, &new->thread_flags);new->thread_fn = new->handler;new->handler = irq_default_primary_handler;return 0;
}

setup_irq()、request_threaded_irq()、request_irq()都是对__setup_irq()的包裹。

request_irq()调用request_threaded_irq()，只是少了thread_fn。

request_thraded_irq()和setup_irq()的区别在于，setup_irq()入参是struct irqaction ，而request_threaded_irq()在内部组装struct irqaction。

6. 一个中断的生命

经过上面的分析可以看出一个中断从产生、执行，到最终结束的流程。这里我们用树形代码路径来简要分析一下一个中断的生命周期。

vector_irq()->vector_irq()->__irq_svc()->svc_entry()---------------------------------------------------------------保护中断现场->irq_handler()->gic_handle_irq()--------------------------------------------具体到GIC中断控制器对应的就是gic_handle_irq()，此处从架构相关进入了GIC相关处理。->GIC_CPU_INTACK------------------------------------------------读取IAR寄存器，响应中断->handle_domain_irq()->irq_enter()--------------------------------------------------------进入硬中断上下文->generic_handle_irq()->generic_handle_irq_desc()->handle_fasteoi_irq()--------------------根据中断号分辨不同类型的中断，对应不同处理函数，这里中断号取大于等于32。->handle_irq_event()->handle_irq_event_percpu()->action->handler()---------------------------对应到特定中断的处理函数，即上半部->__irq_wake_thread()-----------------------------------------------------如果中断函数处理返回IRQ_WAKE_THREAD，则唤醒中断线程进行处理，但不是立即执行中断线程。->irq_exit()---------------------------------------退出硬中断上下文。视情况处理软中断。->invoke_softirq()-----------------处理软中断，超出一定条件任务就会交给软中断线程处理。->GIC_CPU_EOI--------------------------写EOI寄存器，表示结束中断。至此GIC才会接收新的硬件中断，此前一直是屏蔽硬件中断的。->svc_exit-----------------------------------------------------------------恢复中断现场

从上面的分析可以看出：

中断上半部的处理是关硬件中断的，这里的关硬件中断是GIC就不接收中断处理。直到写EOI之后，GIC仲裁单元才会重新选择中断进行处理。
软中断运行于软中断上下文中，但是仍然是关硬件中断的，这里需要特别注意，软中断需要快速处理并且不能睡眠。
不是所有软中断都运行于软中断上下文中，部分软中断任务可能会交给ksoftirqd线程处理。
包括IRQ_WAKE_THREAD、ksoftirqd、woker等唤醒线程的情况，都不会在中断上下文中进行处理。中断上下文中所做的处理只是唤醒，执行时机交给系统调度。
如果要提高Linux实时性，有两个要点：一是将上半部线程化；另一个是将软中断都交给ksoftirqd线程处理。

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