一、spi_device结构体

/*** struct spi_device - Controller side proxy for an SPI slave device* @dev: Driver model representation of the device.* @controller: SPI controller used with the device.* @master: Copy of controller, for backwards compatibility.* @max_speed_hz: Maximum clock rate to be used with this chip* (on this board); may be changed by the device's driver.*   The spi_transfer.speed_hz can override this for each transfer.* @chip_select: Chipselect, distinguishing chips handled by @controller.* @mode: The spi mode defines how data is clocked out and in.* This may be changed by the device's driver.*   The "active low" default for chipselect mode can be overridden*   (by specifying SPI_CS_HIGH) as can the "MSB first" default for*   each word in a transfer (by specifying SPI_LSB_FIRST).* @bits_per_word: Data transfers involve one or more words; word sizes*  like eight or 12 bits are common.  In-memory wordsizes are* powers of two bytes (e.g. 20 bit samples use 32 bits).* This may be changed by the device's driver, or left at the*    default (0) indicating protocol words are eight bit bytes.* The spi_transfer.bits_per_word can override this for each transfer.* @irq: Negative, or the number passed to request_irq() to receive* interrupts from this device.* @controller_state: Controller's runtime state* @controller_data: Board-specific definitions for controller, such as*   FIFO initialization parameters; from board_info.controller_data* @modalias: Name of the driver to use with this device, or an alias*   for that name.  This appears in the sysfs "modalias" attribute*   for driver coldplugging, and in uevents used for hotplugging* @cs_gpio: gpio number of the chipselect line (optional, -ENOENT when*    not using a GPIO line)** @statistics: statistics for the spi_device** A @spi_device is used to interchange data between an SPI slave* (usually a discrete chip) and CPU memory.** In @dev, the platform_data is used to hold information about this* device that's meaningful to the device's protocol driver, but not* to its controller.  One example might be an identifier for a chip* variant with slightly different functionality; another might be* information about how this particular board wires the chip's pins.*/
struct spi_device {struct device        dev;struct spi_controller   *controller;struct spi_controller   *master;    /* compatibility layer */u32            max_speed_hz;       //该设备能支持的SPI设备的最大时钟u8           chip_select;        //在spi_master下的第几个设备，在spi_master中有一个cs_gpio数组，里面存放了各个spi设备的片选引脚，//spi_device的片选引脚就是:cs_gpios[spi_device.chip_select]u8         bits_per_word;      //每个基本的SPI传输涉及多少位,在使用spi控制器时，一般往寄存器里写入数据，SPI控制器会一位一位地发送出去。//一个寄存器是32位，通常叫word。寄存器里有多少位会被发送出去，这取决于bits_per_word。//扩展：bits_per_word可以大于32位，这适用于DMA突发模式u16           mode;
#define SPI_CPHA    0x01            /* clock phase */       //采样周期，第一个周期还是第二个周期
#define SPI_CPOL    0x02            /* clock polarity */    //平时的时钟极性
#define SPI_MODE_0  (0|0)           /* (original MicroWire) */  //组合起来有四种，SCK平时为低电平，第1个周期采样
#define SPI_MODE_1  (0|SPI_CPHA)        //SCK为低，第2个周期采样
#define SPI_MODE_2  (SPI_CPOL|0)        //SCK为高电平，第1个周期采样
#define SPI_MODE_3  (SPI_CPOL|SPI_CPHA)     //SCK平时为高电平，第2个周期采样
#define SPI_CS_HIGH 0x04            /* chipselect active high? */       //引脚信号高电平有效
#define SPI_LSB_FIRST   0x08            /* per-word bits-on-wire */     //一般来说都是MSB，高位先传输。这个表示低位先传输。有些SPI设备并不支持低位传输
#define SPI_3WIRE   0x10            /* SI/SO signals shared */      //SDO、SDI共用一条线
#define SPI_LOOP    0x20            /* loopback mode */         //回环模式，SDO、SDI连接在一起
#define SPI_NO_CS   0x40            /* 1 dev/bus, no chipselect */  //只有一个spi设备，没有片选，也不需要
#define SPI_READY   0x80            /* slave pulls low to pause */  //spi信号可以拉低信号，表示暂停、表示未就绪
#define SPI_TX_DUAL 0x100           /* transmit with 2 wires */     //发送数据时有2条信号线
#define SPI_TX_QUAD 0x200           /* transmit with 4 wires */     //发送数据时有4条信号线
#define SPI_RX_DUAL 0x400           /* receive with 2 wires */      //接收数据时有2条信号线
#define SPI_RX_QUAD 0x800           /* receive with 4 wires */      //接收数据时有4条信号线int            irq;void            *controller_state;void          *controller_data;char           modalias[SPI_NAME_SIZE];int         cs_gpio;    /* chip select gpio */  //可选项，也可以把spi_device的片选引脚记录在这里/* the statistics */struct spi_statistics  statistics;/** likely need more hooks for more protocol options affecting how* the controller talks to each chip, like:*  - memory packing (12 bit samples into low bits, others zeroed)*  - priority*  - drop chipselect after each word*  - chipselect delays*  - ...*/
};

二、SPI设备树格式

对于SPI master，就是SPI控制器，它下面可以连接多个SPI设备。
在设备树里，使用一个节点来表示SPI Master，使用子节点来表示挂在下面的SPI设备

2.1 SPI Master

必须的属性：

#address-cells:这个SPI Master下的SPI设备，需要多少个cell来表述它的片选引脚
#size-cells:必须设置为0
compatible:根据它找到SPI Master驱动
可选属性：
cs-gpios: SPI Master可以使用多个GPIO当作片选，可以在这个属性列出那些GPIO
num-cs: 片选引脚总数
其他属性和驱动程序相关，不同SPI Master驱动程序要求的属性不一样

2.2 SPI device

在对应的SPI Master设备树节点下，每一个节点都对应一个SPI设备，
这些SPI Device必选的属性如下：

compatible：根据它找到SPI Device驱动
reg：用来表示它使用哪个片选引脚
spi-max-frequency：必选，该SPI设备支持的最大SPI时钟
可选属性如下：
spi-cpol：这是一个空属性（没有值），表示CPOL为1，即平时SPI时钟为低电平
spi-cpha：这是一个空属性（没有值），表示CPHA为1，即在时钟的第2个边沿采样数据
spi-cs-high：这是一个空属性（没有值），表示片选引脚高电平有效
spi-3wire：这是一个空属性（没有值），表示使用SPI 三线模式
spi-lsb-first：这是一个空属性（没有值），表示使用SPI传输数据时先传输最低为（LSB）
spi-tx-bus-width：表示有几条MOSI引脚，没有这个属性时默认只有1条MOSI引脚
spi-rx-bus-width：表示有几条MISO引脚，没有这个属性时默认只有1条MISO引脚
spi-rx-delay-us：单位时毫秒，表示每次读传输后要延时多久
spi-tx-delay-us：单位时毫秒，表示每次写传输后要延时多久

2.3 设备树示例

 spi@f00 {              //表示一个spi_master#address-cells = <1>;            //reg属性需要多上长度描述#size-cells = <0>;            //必须是0compatible = "fsl,mpc5200b-spi","fsl,mpc5200-spi";       //用于匹配spi_master驱动程序reg = <0xf00 0x20>;interrupts = <2 13 0 2 14 0>;interrupt-parent = <&mpc5200_pic>;//cs-gpios = <&gpio1 0 0>, <0>, <&gpio1 1 0>, <&gpio1 2 0>; 可以定义使用多少个片选引脚ethernet-switch@0 {           //表示挂载在spi下的设备0compatible = "micrel,ks8995m";spi-max-frequency = <1000000>;       //spi的最大频率reg = <0>;};codec@1 {             //表示挂载在spi下的设备1compatible = "ti,tlv320aic26";spi-max-frequency = <100000>;reg = <1>;};};

三、设备树实例

在设备树里，会有一个节点用来表示SPI控制器
在这个SPI控制器下面，连接有哪些SPI设备？会在设备树里使用子节点来描述SPI设备

3.1 使用GPIO模拟的SPI控制器

spi3{compatible = "spi-gpio";status = "okay";gpio-sck = <&gpio0 5 GPIO_ACTIVE_LOW>;gpio-mosi = <&gpio1 15 GPIO_ACTIVE_LOW>;cs-gpio = <&gpio0 27 GPIO_ACTIVE_LOW>;num-chipselects = <1>;#address-cells = <1>;#size-cells = <0>;gpio_spi: gpio_spi@0 {compatible = "fairchild,74hc595";gpio-controller;#gpio-cells = <2>;reg = <0>;registers-number = <1>;spi-max-frequency = <100000>;};
};

驱动中的调用：

//driver/spi/spi-gpio.c
//在compatible="spi-gpio"匹配后，调用probe函数
static int spi_gpio_probe(struct platform_device *pdev)
{int                status;struct spi_master        *master;struct spi_gpio         *spi_gpio;struct spi_gpio_platform_data *pdata;u16 master_flags = 0;bool use_of = 0;status = spi_gpio_probe_dt(pdev);//...pdata = dev_get_platdata(&pdev->dev);//分配一个spi_mastermaster = spi_alloc_master(&pdev->dev, sizeof(*spi_gpio));//...spi_gpio = spi_master_get_devdata(master);spi_gpio->cs_gpios = devm_kcalloc(&pdev->dev,pdata->num_chipselect,sizeof(*spi_gpio->cs_gpios),GFP_KERNEL);//....status = spi_gpio_request(&pdev->dev, spi_gpio,pdata->num_chipselect, &master_flags);//...设置spi_mastermaster->bits_per_word_mask = SPI_BPW_RANGE_MASK(1, 32);master->mode_bits = SPI_3WIRE | SPI_CPHA | SPI_CPOL;master->flags = master_flags;master->bus_num = pdev->id;/* The master needs to think there is a chipselect even if not connected */master->num_chipselect = spi_gpio->has_cs ? pdata->num_chipselect : 1;master->setup = spi_gpio_setup;master->cleanup = spi_gpio_cleanup;
#ifdef CONFIG_OFmaster->dev.of_node = pdev->dev.of_node;
#endifspi_gpio->bitbang.master = master;spi_gpio->bitbang.chipselect = spi_gpio_chipselect;spi_gpio->bitbang.set_line_direction = spi_gpio_set_direction;if ((master_flags & SPI_MASTER_NO_TX) == 0) {spi_gpio->bitbang.txrx_word[SPI_MODE_0] = spi_gpio_txrx_word_mode0;spi_gpio->bitbang.txrx_word[SPI_MODE_1] = spi_gpio_txrx_word_mode1;spi_gpio->bitbang.txrx_word[SPI_MODE_2] = spi_gpio_txrx_word_mode2;spi_gpio->bitbang.txrx_word[SPI_MODE_3] = spi_gpio_txrx_word_mode3;} else {spi_gpio->bitbang.txrx_word[SPI_MODE_0] = spi_gpio_spec_txrx_word_mode0;spi_gpio->bitbang.txrx_word[SPI_MODE_1] = spi_gpio_spec_txrx_word_mode1;spi_gpio->bitbang.txrx_word[SPI_MODE_2] = spi_gpio_spec_txrx_word_mode2;spi_gpio->bitbang.txrx_word[SPI_MODE_3] = spi_gpio_spec_txrx_word_mode3;}spi_gpio->bitbang.setup_transfer = spi_bitbang_setup_transfer;spi_gpio->bitbang.flags = SPI_CS_HIGH;//这里注册spi_masterstatus = spi_bitbang_start(&spi_gpio->bitbang);if (status)spi_master_put(master);return status;
}int spi_bitbang_start(struct spi_bitbang *bitbang)
{struct spi_master *master = bitbang->master;int ret;//....注册spi_masterret = spi_register_master(spi_master_get(master));//...return 0;
}

3.2 IMX6ULL SPI控制器

arch/arm/boot/dts/imx6ull.dtsi

ecspi3: ecspi@02010000 {#address-cells = <1>;#size-cells = <0>;compatible = "fsl,imx6ul-ecspi","fsl,imx5l-ecspi";reg = <0x02010000> <0x4000>;interrupts = <GIC_SPI 33 IRQ_TYPE_LEVEL_HIGH>;clocks = <&clks IMX6UL_CLK_ECSPI3>,<&clks IMX6UL_CLK_ECSPI3>;clock-names = "jpg", "per";dmas = <&sdma 7 7 1>, <&sdma 8 7 2>;dma-names = "rx", "tx";status = "disabled";
};

arch/arm/boot/dts/100ask_imx6ull-14x14.dts

&ecspi3 {pinctrl-names = "default";pinctrl-0 = <&pinctrl_ecspi3>;cs-gpios = <&gpio1 20 GPIO_ACTIVE_LOW>;status = "okay";spidev: icm20608@0 {compatible = "invensense,icm20608";interrupt-parent = <&gpio1>;interrupts = <1 1>;spi-max-frequency = <8000000>;reg = <0>;};
};

3.3 STM32MP157 SPI控制器

arch/arm/boot/dts/stm32mp151.dtsi

spi5: spi@44009000 {#address-cells = <1>;#size-cells = <0>;compatible = "st,stm32h7-spi";reg = <0x44009000 0x400>;interrupts = <GIC_SPI 85 IRQ_TYPE_LEVEL_HIGH>;clocks = <&rcc SPI5_K>;resets = <&rcc SPI5_R>;dmas = <&dmamux1 85 0x400 0x01>,<&dmamux1 86 0x400 0x01>;dma-names = "rx", "tx";power-domains = <&pd_core>;status = "disabled";
};

arch/arm/boot/dts/stm32mp157c-100ask-512d-lcd-v1.dts

&spi5 {pinctrl-names = "default", "sleep";pinctrl-0 = <&spi5_pins_a>;pinctrl-1 = <&spi5_sleep_pins_a>;status = "okay";cs-gpios = <&gpioh 5 GPIO_ACTIVE_LOW>;spidev: icm20608@0 {compatible = "invensense,icm20608";interrupts = <0 IRQ_TYPE_EDGE_FALLING>;interrupt-parent = <&gpioz>;spi-max-frequency = <8000000>;reg = <0>;};
};

四、设备树处理过程

在注册spi_master时，调用spi_register_controller

int spi_register_controller(struct spi_controller *ctlr)
{//...注册spi_masterif (!spi_controller_is_slave(ctlr)) {status = of_spi_register_master(ctlr);if (status)return status;}//...注册完master注册device/* Register devices from the device tree and ACPI */of_register_spi_devices(ctlr);acpi_register_spi_devices(ctlr);
done:return status;
}

内核源码：drivers/spi/spi.c

static int of_spi_register_master(struct spi_controller *ctlr)
{int nb, i, *cs;struct device_node *np = ctlr->dev.of_node;if (!np)return 0;nb = of_gpio_named_count(np, "cs-gpios");        //解析片选引脚节点ctlr->num_chipselect = max_t(int, nb, ctlr->num_chipselect);/* Return error only for an incorrectly formed cs-gpios property */if (nb == 0 || nb == -ENOENT)return 0;else if (nb < 0)return nb;cs = devm_kcalloc(&ctlr->dev, ctlr->num_chipselect, sizeof(int),GFP_KERNEL);ctlr->cs_gpios = cs;      //把片选引脚信息记录在这里if (!ctlr->cs_gpios)return -ENOMEM;for (i = 0; i < ctlr->num_chipselect; i++)cs[i] = -ENOENT;for (i = 0; i < nb; i++)cs[i] = of_get_named_gpio(np, "cs-gpios", i);return 0;
}//解析每个spi_device
static void of_register_spi_devices(struct spi_controller *ctlr)
{//...for_each_available_child_of_node(ctlr->dev.of_node, nc) {if (of_node_test_and_set_flag(nc, OF_POPULATED))continue;spi = of_register_spi_device(ctlr, nc);     //对每个节点进行解析//...}
}static struct spi_device *
of_register_spi_device(struct spi_controller *ctlr, struct device_node *nc)
{struct spi_device *spi;int rc;/* Alloc an spi_device */spi = spi_alloc_device(ctlr);//.../* Select device driver */rc = of_modalias_node(nc, spi->modalias,sizeof(spi->modalias));//...rc = of_spi_parse_dt(ctlr, spi, nc);       //这里解析spi_device节点的所有属性//.../* Store a pointer to the node in the device structure */of_node_get(nc);spi->dev.of_node = nc;/* Register the new device */rc = spi_add_device(spi);//...return spi;//...
}

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