二十、SPI设备驱动及应用(一)
先给出Linux SPI子系统的体系结构图:
SPI子系统体系结构
下面开始分析SPI子系统。
Linux中SPI子系统的初始化是从drivers/spi/spi.c文件中的spi_init函数开始的,看看它的定义:
00001025 static int __init spi_init(void)
00001026 {
00001027 int status;
00001028
00001029 buf = kmalloc(SPI_BUFSIZ, GFP_KERNEL);
00001030 if (!buf) {
00001031 status = -ENOMEM;
00001032 goto err0;
00001033 }
00001034
00001035 status = bus_register(&spi_bus_type);
00001036 if (status < 0)
00001037 goto err1;
00001038
00001039 status = class_register(&spi_master_class);
00001040 if (status < 0)
00001041 goto err2;
00001042 return 0;
00001043
00001044 err2:
00001045 bus_unregister(&spi_bus_type);
00001046 err1:
00001047 kfree(buf);
00001048 buf = NULL;
00001049 err0:
00001050 return status;
00001051 }
1029行,分配spi buf内存,其中buf和SPI_BUFSIZ都在spi.c文件中定义:
00000945 #define SPI_BUFSIZ max(32,SMP_CACHE_BYTES)
00000946
00000947 static u8 *buf;
1035行,注册spi总线,同样是在spi.c文件中:
00000145 struct bus_type spi_bus_type = {
00000146 .name = "spi",
00000147 .dev_attrs = spi_dev_attrs,
00000148 .match = spi_match_device,
00000149 .uevent = spi_uevent,
00000150 .suspend = spi_suspend,
00000151 .resume = spi_resume,
00000152 };
146行,总线的名字就叫spi。
148行,比较重要的,spi_match_device是spi总线上匹配设备和设备驱动的函数,同样是在spi.c文件中:
00000085 static int spi_match_device(struct device *dev, struct device_driver *drv)
00000086 {
00000087 const struct spi_device *spi = to_spi_device(dev);
00000088 const struct spi_driver *sdrv = to_spi_driver(drv);
00000089
00000090 /* Attempt an OF style match */
00000091 if (of_driver_match_device(dev, drv))
00000092 return 1;
00000093
00000094 if (sdrv->id_table)
00000095 return !!spi_match_id(sdrv->id_table, spi);
00000096
00000097 return strcmp(spi->modalias, drv->name) == 0;
00000098 }
写过驱动的都应该知道platform总线有struct platform_device和struct platform_driver,到了SPI总线,当然也有对应的struct spi_device和struct spi_driver,如87、88行所示。87行,关于struct spi_device的定义是在include/linux/spi/spi.h中:
00000069 struct spi_device {
00000070 struct device dev;
00000071 struct spi_master *master;
00000072 u32 max_speed_hz;
00000073 u8 chip_select;
00000074 u8 mode;
00000075 #define SPI_CPHA 0x01 /* clock phase */
00000076 #define SPI_CPOL 0x02 /* clock polarity */
00000077 #define SPI_MODE_0 (0|0) /* (original MicroWire) */
00000078 #define SPI_MODE_1 (0|SPI_CPHA)
00000079 #define SPI_MODE_2 (SPI_CPOL|0)
00000080 #define SPI_MODE_3 (SPI_CPOL|SPI_CPHA)
00000081 #define SPI_CS_HIGH 0x04 /* chipselect active high? */
00000082 #define SPI_LSB_FIRST 0x08 /* per-word bits-on-wire */
00000083 #define SPI_3WIRE 0x10 /* SI/SO signals shared */
00000084 #define SPI_LOOP 0x20 /* loopback mode */
00000085 #define SPI_NO_CS 0x40 /* 1 dev/bus, no chipselect */
00000086 #define SPI_READY 0x80 /* slave pulls low to pause */
00000087 u8 bits_per_word;
00000088 int irq;
00000089 void *controller_state;
00000090 void *controller_data;
00000091 char modalias[SPI_NAME_SIZE];
00000092
00000093 /*
00000094 * likely need more hooks for more protocol options affecting how
00000095 * the controller talks to each chip, like:
00000096 * - memory packing (12 bit samples into low bits, others zeroed)
00000097 * - priority
00000098 * - drop chipselect after each word
00000099 * - chipselect delays
00000100 * - ...
00000101 */
00000102 };
70行,dev,嵌入到设备模型中用的。
71行,master,spi设备的更高层描述,每一个spi控制器就对应一个master,一个spi设备必须对应一个master,master下可以有多个spi设备。
72,73行没什么好说的,从变量的名字就可以明白。
74行,mode,针对时钟相位CPHA(0或1)和时钟极性CPOL(0或1)的不同组合,将spi分成四种模式,就是77至80行这四种。CPOL表示当空闲时(没有进行数据传输)时钟信号的电平,CPOL=0表示低电平,CPOL=1表示高电平。每个时钟周期都有两次电平的跳变,上升沿和下降沿,CPHA就表示在每个时钟周期里是第一个边沿采样数据还是第二个边沿采样数据,具体第一个边沿或者第二个边沿是上升沿还是下降沿则由CPOL决定。看下面这张图就明白了。蓝色箭头表示对数据进行采样。
87行,如果传输是以字节为单位的话就设置为8,相应地,如果是以2个字节为单位则设置为16。
88行,中断号。89行,没有使用,在后面会看到这个值会被设置为NULL。90行,后面讲到具体的控制器再说。91行,很重要,一般来说设备与驱动能否匹配起来就要看它,注意,这里只是说一般,因为还有另外两种匹配的方法,不过大部分设备和驱动能否匹配起来都是根据名字是否相等,当然像USB驱动就不是根据名字来匹配的,而是根据与id table。struct spi_driver的定义也是在include/linux/spi/spi.h:
00000175 struct spi_driver {
00000176 const struct spi_device_id *id_table;
00000177 int (*probe)(struct spi_device *spi);
00000178 int (*remove)(struct spi_device *spi);
00000179 void (*shutdown)(struct spi_device *spi);
00000180 int (*suspend)(struct spi_device *spi, pm_message_t mesg);
00000181 int (*resume)(struct spi_device *spi);
00000182 struct device_driver driver;
00000183 };
182行,driver就是在设备模型中使用的那个device_driver,其他都是一些函数指针的定义,挺熟悉的了,就不多说了。
回到spi_match_device函数,91行和95行就是设备和驱动匹配的另外两种方法,因为后文要讲的spi驱动使用的是第三种方法,因此这里就不讨论这两种方法了。97行,根据设备名和驱动名是否相等进行匹配,相等则返回1,表示匹配成功,此时驱动里的probe函数将会被调用,这也是我们最希望看到的,返回0则表示匹配失败。
我们知道,对于具体的平台,nand、iic、frame buffer等这些都是平台设备,spi当然也一样是平台设备,对于平台设备,大部分情况下是先注册设备再注册驱动。因此下面就以exynos4412为具体平台,按照这种先后顺序来讲述。
exynos4412有三个SPI控制器,以SPI0为例就可以了。首先看exynos4412中关于SPI0控制器的描述,在arch/arm/mach-exynos/dev-spi.c文件中:
struct platform_device exynos_device_spi0 = {.name = "s3c64xx-spi",.id = 0,.num_resources = ARRAY_SIZE(exynos_spi0_resource),.resource = exynos_spi0_resource,.dev = {.dma_mask = &spi_dmamask,.coherent_dma_mask = DMA_BIT_MASK(32),.platform_data = &exynos_spi0_pdata,},
};
第2行,驱动能否与这个设备匹配,就看这个名字了,因此对应的驱动名字必须与之一样。3行,SPI控制器的ID,SPI0控制器就为0,SPI1控制器就为1。
4和5行是关于IO口资源、DMA资源和中断资源的。7、8行是关于DMA的,不说了。9行,给驱动用的,在驱动那里再说。在板初始化函数smdk4x12_machine_init里调用platform_add_devices函数就可以将SPI0设备注册到platform总线上。
exynos4412的SPI控制器驱动在drivers/spi/spi_s3c64xx.c文件里(虽然我们是exynos4412平台,但是上面exynos_device_spi0中name为"s3c64xx-spi",所以,我猜这应该是使用的s3c6410原来的驱动程序)。初始化函数:
00001183 static int __init s3c64xx_spi_init(void)
00001184 {
00001185 return platform_driver_probe(&s3c64xx_spi_driver, s3c64xx_spi_probe);
00001186 }
1185行,s3c64xx_spi_driver是struct platform_driver的实例,也在spi_s3c64xx.c文件中定义:
00001172 static struct platform_driver s3c64xx_spi_driver = {
00001173 .driver = {
00001174 .name = "s3c64xx-spi",
00001175 .owner = THIS_MODULE,
00001176 },
00001177 .remove = s3c64xx_spi_remove,
00001178 .suspend = s3c64xx_spi_suspend,
00001179 .resume = s3c64xx_spi_resume,
00001180 };
1174行,看到了没?和之前在exynos_device_spi0里定义的名字是一样的,这样它们就可以匹配起来,1185行的s3c64xx_spi_probe驱动探测函数就会被调用,看下它的定义:
00000911 static int __init s3c64xx_spi_probe(struct platform_device *pdev)
00000912 {
00000913 struct resource *mem_res, *dmatx_res, *dmarx_res;
00000914 struct s3c64xx_spi_driver_data *sdd;
00000915 struct s3c64xx_spi_info *sci;
00000916 struct spi_master *master;
00000917 int ret;
00000918
00000919 if (pdev->id < 0) {
00000920 dev_err(&pdev->dev,
00000921 "Invalid platform device id-%d\n", pdev->id);
00000922 return -ENODEV;
00000923 }
00000924
00000925 if (pdev->dev.platform_data == NULL) {
00000926 dev_err(&pdev->dev, "platform_data missing!\n");
00000927 return -ENODEV;
00000928 }
00000929
00000930 sci = pdev->dev.platform_data;
00000931 if (!sci->src_clk_name) {
00000932 dev_err(&pdev->dev,
00000933 "Board init must call s3c64xx_spi_set_info()\n");
00000934 return -EINVAL;
00000935 }
00000936
00000937 /* Check for availability of necessary resource */
00000938
00000939 dmatx_res = platform_get_resource(pdev, IORESOURCE_DMA, 0);
00000940 if (dmatx_res == NULL) {
00000941 dev_err(&pdev->dev, "Unable to get SPI-Tx dma resource\n");
00000942 return -ENXIO;
00000943 }
00000944
00000945 dmarx_res = platform_get_resource(pdev, IORESOURCE_DMA, 1);
00000946 if (dmarx_res == NULL) {
00000947 dev_err(&pdev->dev, "Unable to get SPI-Rx dma resource\n");
00000948 return -ENXIO;
00000949 }
00000950
00000951 mem_res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
00000952 if (mem_res == NULL) {
00000953 dev_err(&pdev->dev, "Unable to get SPI MEM resource\n");
00000954 return -ENXIO;
00000955 }
00000956
00000957 master = spi_alloc_master(&pdev->dev,
00000958 sizeof(struct s3c64xx_spi_driver_data));
00000959 if (master == NULL) {
00000960 dev_err(&pdev->dev, "Unable to allocate SPI Master\n");
00000961 return -ENOMEM;
00000962 }
00000963
00000964 platform_set_drvdata(pdev, master);
00000965
00000966 sdd = spi_master_get_devdata(master);
00000967 sdd->master = master;
00000968 sdd->cntrlr_info = sci;
00000969 sdd->pdev = pdev;
00000970 sdd->sfr_start = mem_res->start;
00000971 sdd->tx_dmach = dmatx_res->start;
00000972 sdd->rx_dmach = dmarx_res->start;
00000973
00000974 sdd->cur_bpw = 8;
00000975
00000976 master->bus_num = pdev->id;
00000977 master->setup = s3c64xx_spi_setup;
00000978 master->transfer = s3c64xx_spi_transfer;
00000979 master->num_chipselect = sci->num_cs;
00000980 master->dma_alignment = 8;
00000981 /* the spi->mode bits understood by this driver: */
00000982
00000983 master->mode_bits = SPI_CPOL | SPI_CPHA | SPI_CS_HIGH;
00000984
00000985 if (request_mem_region(mem_res->start,
00000986 resource_size(mem_res), pdev->name) == NULL) {
00000987 dev_err(&pdev->dev, "Req mem region failed\n");
00000988 ret = -ENXIO;
00000989 goto err0;
00000990 }
00000991
00000992 sdd->regs = ioremap(mem_res->start, resource_size(mem_res));
00000993 if (sdd->regs == NULL) {
00000994 dev_err(&pdev->dev, "Unable to remap IO\n");
00000995 ret = -ENXIO;
00000996 goto err1;
00000997 }
00000998
00000999 if (sci->cfg_gpio == NULL || sci->cfg_gpio(pdev)) {
00001000 dev_err(&pdev->dev, "Unable to config gpio\n");
00001001 ret = -EBUSY;
00001002 goto err2;
00001003 }
00001004
00001005 /* Setup clocks */
00001006 sdd->clk = clk_get(&pdev->dev, "spi");
00001007 if (IS_ERR(sdd->clk)) {
00001008 dev_err(&pdev->dev, "Unable to acquire clock 'spi'\n");
00001009 ret = PTR_ERR(sdd->clk);
00001010 goto err3;
00001011 }
00001012
00001013 if (clk_enable(sdd->clk)) {
00001014 dev_err(&pdev->dev, "Couldn't enable clock 'spi'\n");
00001015 ret = -EBUSY;
00001016 goto err4;
00001017 }
00001018
00001019 sdd->src_clk = clk_get(&pdev->dev, sci->src_clk_name);
00001020 if (IS_ERR(sdd->src_clk)) {
00001021 dev_err(&pdev->dev,
00001022 "Unable to acquire clock '%s'\n", sci->src_clk_name);
00001023 ret = PTR_ERR(sdd->src_clk);
00001024 goto err5;
00001025 }
00001026
00001027 if (clk_enable(sdd->src_clk)) {
00001028 dev_err(&pdev->dev, "Couldn't enable clock '%s'\n",
00001029 sci->src_clk_name);
00001030 ret = -EBUSY;
00001031 goto err6;
00001032 }
00001033
00001034 sdd->workqueue = create_singlethread_workqueue(
00001035 dev_name(master->dev.parent));
00001036 if (sdd->workqueue == NULL) {
00001037 dev_err(&pdev->dev, "Unable to create workqueue\n");
00001038 ret = -ENOMEM;
00001039 goto err7;
00001040 }
00001041
00001042 /* Setup Deufult Mode */
00001043 s3c64xx_spi_hwinit(sdd, pdev->id);
00001044
00001045 spin_lock_init(&sdd->lock);
00001046 init_completion(&sdd->xfer_completion);
00001047 INIT_WORK(&sdd->work, s3c64xx_spi_work);
00001048 INIT_LIST_HEAD(&sdd->queue);
00001049
00001050 if (spi_register_master(master)) {
00001051 dev_err(&pdev->dev, "cannot register SPI master\n");
00001052 ret = -EBUSY;
00001053 goto err8;
00001054 }
00001055
00001056 dev_dbg(&pdev->dev, "Samsung SoC SPI Driver loaded for Bus SPI-%d "
00001057 "with %d Slaves attached\n",
00001058 pdev->id, master->num_chipselect);
00001059 dev_dbg(&pdev->dev, "\tIOmem=[0x%x-0x%x]\tDMA=[Rx-%d, Tx-%d]\n",
00001060 mem_res->end, mem_res->start,
00001061 sdd->rx_dmach, sdd->tx_dmach);
00001062
00001063 return 0;
00001064
00001065 err8:
00001066 destroy_workqueue(sdd->workqueue);
00001067 err7:
00001068 clk_disable(sdd->src_clk);
00001069 err6:
00001070 clk_put(sdd->src_clk);
00001071 err5:
00001072 clk_disable(sdd->clk);
00001073 err4:
00001074 clk_put(sdd->clk);
00001075 err3:
00001076 err2:
00001077 iounmap((void *) sdd->regs);
00001078 err1:
00001079 release_mem_region(mem_res->start, resource_size(mem_res));
00001080 err0:
00001081 platform_set_drvdata(pdev, NULL);
00001082 spi_master_put(master);
00001083
00001084 return ret;
00001085 }
函数很长,但做的东西却很简单。919至923行,SPI控制器的ID是从0开始的,小于0的话,没门,出错。
925至928行,必须要有platform_data,否则出错。930行,如果platform_data存在的话就把它取出来。
931至935行,如果src_clk_name为0,则表示在板初始化函数里没有调用s3c64xx_spi_set_info函数。
939至955行,获取在设备里定义的IO口和DMA资源。
957至962行,一个SPI控制器用一个master来描述。这里使用SPI核心的spi_alloc_master函数请求分配master。它在drivers/spi/spi.c文件中定义:
00000471 struct spi_master *spi_alloc_master(struct device *dev, unsigned size)
00000472 {
00000473 struct spi_master *master;
00000474
00000475 if (!dev)
00000476 return NULL;
00000477
00000478 master = kzalloc(size + sizeof *master, GFP_KERNEL);
00000479 if (!master)
00000480 return NULL;
00000481
00000482 device_initialize(&master->dev);
00000483 master->dev.class = &spi_master_class;
00000484 master->dev.parent = get_device(dev);
00000485 spi_master_set_devdata(master, &master[1]);
00000486
00000487 return master;
00000488 }
478至480行,这里分配的内存大小是*master加size,包含了两部分内存。
482行,设备模型中的初始设备函数,不说。
483行,spi_master_class在SPI子系统初始化的时候就已经注册好了。
484行,设置当前设备的父设备,关于设备模型的。
485行,&master[1]就是master之后的另一部分内存的起始地址。
回到s3c64xx_spi_probe函数,966行,就是取出刚才申请的第二部分内存的起始地址。
966至980行,根据预先定义的变量、函数进行填充。
983行,有点意思,说明该驱动支持哪些SPI模式。
985至997行,写过Linux驱动都应该知道,IO内存映射。
999至1003行,SPI IO管脚配置,将相应的IO管脚设置为SPI功能。
1006至1032行,使能SPI时钟。
1034至1040行,创建单个线程的工作队列,用于数据收发操作。
1043行,硬件初始化,初始化SPI控制器寄存器。
1045至1048行,锁,工作队列等初始化。
1050至1054行,spi_register_master在drivers/spi/spi.c文件中定义:
00000511 int spi_register_master(struct spi_master *master)
00000512 {
00000513 static atomic_t dyn_bus_id = ATOMIC_INIT((1<<15) - 1);
00000514 struct device *dev = master->dev.parent;
00000515 int status = -ENODEV;
00000516 int dynamic = 0;
00000517
00000518 if (!dev)
00000519 return -ENODEV;
00000520
00000521 /* even if it's just one always-selected device, there must
00000522 * be at least one chipselect
00000523 */
00000524 if (master->num_chipselect == 0)
00000525 return -EINVAL;
00000526
00000527 /* convention: dynamically assigned bus IDs count down from the max */
00000528 if (master->bus_num < 0) {
00000529 /* FIXME switch to an IDR based scheme, something like
00000530 * I2C now uses, so we can't run out of "dynamic" IDs
00000531 */
00000532 master->bus_num = atomic_dec_return(&dyn_bus_id);
00000533 dynamic = 1;
00000534 }
00000535
00000536 spin_lock_init(&master->bus_lock_spinlock);
00000537 mutex_init(&master->bus_lock_mutex);
00000538 master->bus_lock_flag = 0;
00000539
00000540 /* register the device, then userspace will see it.
00000541 * registration fails if the bus ID is in use.
00000542 */
00000543 dev_set_name(&master->dev, "spi%u", master->bus_num);
00000544 status = device_add(&master->dev);
00000545 if (status < 0)
00000546 goto done;
00000547 dev_dbg(dev, "registered master %s%s\n", dev_name(&master->dev),
00000548 dynamic ? " (dynamic)" : "");
00000549
00000550 /* populate children from any spi device tables */
00000551 scan_boardinfo(master);
00000552 status = 0;
00000553
00000554 /* Register devices from the device tree */
00000555 of_register_spi_devices(master);
00000556 done:
00000557 return status;
00000558 }
524行,一个SPI控制器至少有一个片选,因此片选数为0则出错。
528至534行,如果总线号小于0则动态分配一个总线号。
543至548行,把master加入到设备模型中。
551行,scan_boardinfo函数同样是在driver/spi/spi.c中定义:
00000414 static void scan_boardinfo(struct spi_master *master)
00000415 {
00000416 struct boardinfo *bi;
00000417
00000418 mutex_lock(&board_lock);
00000419 list_for_each_entry(bi, &board_list, list) {
00000420 struct spi_board_info *chip = bi->board_info;
00000421 unsigned n;
00000422
00000423 for (n = bi->n_board_info; n > 0; n--, chip++) {
00000424 if (chip->bus_num != master->bus_num)
00000425 continue;
00000426 /* NOTE: this relies on spi_new_device to
00000427 * issue diagnostics when given bogus inputs
00000428 */
00000429 (void) spi_new_device(master, chip);
00000430 }
00000431 }
00000432 mutex_unlock(&board_lock);
00000433 }
419至431做了两件事情,首先遍历board_list这个链表,每找到一个成员就将它的总线号与master的总线号进行比较,如果相等则调用spi_new_device函数创建一个spi设备。
00000336 struct spi_device *spi_new_device(struct spi_master *master,
00000337 struct spi_board_info *chip)
00000338 {
00000339 struct spi_device *proxy;
00000340 int status;
00000341
00000342 /* NOTE: caller did any chip->bus_num checks necessary.
00000343 *
00000344 * Also, unless we change the return value convention to use
00000345 * error-or-pointer (not NULL-or-pointer), troubleshootability
00000346 * suggests syslogged diagnostics are best here (ugh).
00000347 */
00000348
00000349 proxy = spi_alloc_device(master);
00000350 if (!proxy)
00000351 return NULL;
00000352
00000353 WARN_ON(strlen(chip->modalias) >= sizeof(proxy->modalias));
00000354
00000355 proxy->chip_select = chip->chip_select;
00000356 proxy->max_speed_hz = chip->max_speed_hz;
00000357 proxy->mode = chip->mode;
00000358 proxy->irq = chip->irq;
00000359 strlcpy(proxy->modalias, chip->modalias, sizeof(proxy->modalias));
00000360 proxy->dev.platform_data = (void *) chip->platform_data;
00000361 proxy->controller_data = chip->controller_data;
00000362 proxy->controller_state = NULL;
00000363
00000364 status = spi_add_device(proxy);
00000365 if (status < 0) {
00000366 spi_dev_put(proxy);
00000367 return NULL;
00000368 }
00000369
00000370 return proxy;
00000371 }
349至351行,spi_alloc_device函数的定义:
00000229 struct spi_device *spi_alloc_device(struct spi_master *master)
00000230 {
00000231 struct spi_device *spi;
00000232 struct device *dev = master->dev.parent;
00000233
00000234 if (!spi_master_get(master))
00000235 return NULL;
00000236
00000237 spi = kzalloc(sizeof *spi, GFP_KERNEL);
00000238 if (!spi) {
00000239 dev_err(dev, "cannot alloc spi_device\n");
00000240 spi_master_put(master);
00000241 return NULL;
00000242 }
00000243
00000244 spi->master = master;
00000245 spi->dev.parent = dev;
00000246 spi->dev.bus = &spi_bus_type;
00000247 spi->dev.release = spidev_release;
00000248 device_initialize(&spi->dev);
00000249 return spi;
00000250 }
234至242行,错误检测和分配内存。
246行,该spi设备属于SPI子系统初始化时注册的那条叫“spi”的总线。
248行,设备模型方面的初始化,不说。
回到spi_new_device函数,355至362行,是一些赋值,其中359行比较关键,设备名字拷贝,362行,之前说过了,设置为NULL。看364行spi_add_device函数的定义:
00000262 int spi_add_device(struct spi_device *spi)
00000263 {
00000264 static DEFINE_MUTEX(spi_add_lock);
00000265 struct device *dev = spi->master->dev.parent;
00000266 struct device *d;
00000267 int status;
00000268
00000269 /* Chipselects are numbered 0..max; validate. */
00000270 if (spi->chip_select >= spi->master->num_chipselect) {
00000271 dev_err(dev, "cs%d >= max %d\n",
00000272 spi->chip_select,
00000273 spi->master->num_chipselect);
00000274 return -EINVAL;
00000275 }
00000276
00000277 /* Set the bus ID string */
00000278 dev_set_name(&spi->dev, "%s.%u", dev_name(&spi->master->dev),
00000279 spi->chip_select);
00000280
00000281
00000282 /* We need to make sure there's no other device with this
00000283 * chipselect **BEFORE** we call setup(), else we'll trash
00000284 * its configuration. Lock against concurrent add() calls.
00000285 */
00000286 mutex_lock(&spi_add_lock);
00000287
00000288 d = bus_find_device_by_name(&spi_bus_type, NULL, dev_name(&spi->dev));
00000289 if (d != NULL) {
00000290 dev_err(dev, "chipselect %d already in use\n",
00000291 spi->chip_select);
00000292 put_device(d);
00000293 status = -EBUSY;
00000294 goto done;
00000295 }
00000296
00000297 /* Drivers may modify this initial i/o setup, but will
00000298 * normally rely on the device being setup. Devices
00000299 * using SPI_CS_HIGH can't coexist well otherwise...
00000300 */
00000301 status = spi_setup(spi);
00000302 if (status < 0) {
00000303 dev_err(dev, "can't %s %s, status %d\n",
00000304 "setup", dev_name(&spi->dev), status);
00000305 goto done;
00000306 }
00000307
00000308 /* Device may be bound to an active driver when this returns */
00000309 status = device_add(&spi->dev);
00000310 if (status < 0)
00000311 dev_err(dev, "can't %s %s, status %d\n",
00000312 "add", dev_name(&spi->dev), status);
00000313 else
00000314 dev_dbg(dev, "registered child %s\n", dev_name(&spi->dev));
00000315
00000316 done:
00000317 mutex_unlock(&spi_add_lock);
00000318 return status;
00000319 }
270至275行,片选号是从0开始的,如果大于或者等于片选数的话则返回出错。
288至295行,遍历spi总线,看是否已经注册过该设备。
301至306行,spi_setup函数的定义:
00000645 int spi_setup(struct spi_device *spi)
00000646 {
00000647 unsigned bad_bits;
00000648 int status;
00000649
00000650 /* help drivers fail *cleanly* when they need options
00000651 * that aren't supported with their current master
00000652 */
00000653 bad_bits = spi->mode & ~spi->master->mode_bits;
00000654 if (bad_bits) {
00000655 dev_dbg(&spi->dev, "setup: unsupported mode bits %x\n",
00000656 bad_bits);
00000657 return -EINVAL;
00000658 }
00000659
00000660 if (!spi->bits_per_word)
00000661 spi->bits_per_word = 8;
00000662
00000663 status = spi->master->setup(spi);
00000664
00000665 dev_dbg(&spi->dev, "setup mode %d, %s%s%s%s"
00000666 "%u bits/w, %u Hz max --> %d\n",
00000667 (int) (spi->mode & (SPI_CPOL | SPI_CPHA)),
00000668 (spi->mode & SPI_CS_HIGH) ? "cs_high, " : "",
00000669 (spi->mode & SPI_LSB_FIRST) ? "lsb, " : "",
00000670 (spi->mode & SPI_3WIRE) ? "3wire, " : "",
00000671 (spi->mode & SPI_LOOP) ? "loopback, " : "",
00000672 spi->bits_per_word, spi->max_speed_hz,
00000673 status);
00000674
00000675 return status;
00000676 }
653至658行,如果驱动不支持该设备的工作模式则返回出错。
663行,调用控制器驱动里的s3c64xx_spi_setup函数,只看前一部分代码:
00000795 static int s3c64xx_spi_setup(struct spi_device *spi)
00000796 {
00000797 struct s3c64xx_spi_csinfo *cs = spi->controller_data;
00000798 struct s3c64xx_spi_driver_data *sdd;
00000799 struct s3c64xx_spi_info *sci;
00000800 struct spi_message *msg;
00000801 u32 psr, speed;
00000802 unsigned long flags;
00000803 int err = 0;
00000804
00000805 if (cs == NULL || cs->set_level == NULL) {
00000806 dev_err(&spi->dev, "No CS for SPI(%d)\n", spi->chip_select);
00000807 return -ENODEV;
00000808 }
00000809
…
从797行就可以知道在实例化struct spi_board_info时,其controller_data成员就应该指向struct s3c64xx_spi_csinfo的对象。
spi_setup函数结束了,回到spi_add_device函数,309至314行,将该设备加入到设备模型。一直后退,回到spi_register_master函数,就剩下555行of_register_spi_devices这个函数,由于本文所讲的驱动没有使用到设备树方面的内容,所以该函数里什么也没做,直接返回。
到这里,SPI控制器驱动的初始化过程已经说完了。接下来要说的是SPI设备驱动。其实Linux中已经实现了一个通用的SPI设备驱动,另外还有一个是用IO口模拟的SPI驱动,在这里,只说前者。
初始化函数是在drivers/spi/spidev.c文件中定义:
00000658 static int __init spidev_init(void)
00000659 {
00000660 int status;
00000661
00000662 /* Claim our 256 reserved device numbers. Then register a class
00000663 * that will key udev/mdev to add/remove /dev nodes. Last, register
00000664 * the driver which manages those device numbers.
00000665 */
00000666 BUILD_BUG_ON(N_SPI_MINORS > 256);
00000667
00000668 status = register_chrdev(SPIDEV_MAJOR, "spi", &spidev_fops);
00000669 if (status < 0)
00000670 return status;
00000671
00000672
00000673 spidev_class = class_create(THIS_MODULE, "spidev");
00000674 if (IS_ERR(spidev_class)) {
00000675 unregister_chrdev(SPIDEV_MAJOR, spidev_spi_driver.driver.name);
00000676 return PTR_ERR(spidev_class);
00000677 }
00000678
00000679 status = spi_register_driver(&spidev_spi_driver);
00000680 if (status < 0) {
00000681 class_destroy(spidev_class);
00000682 unregister_chrdev(SPIDEV_MAJOR, spidev_spi_driver.driver.name);
00000683 }
00000684 return status;
00000685 }
668至670行,注册字符设备,参数spidev_fops是struct file_operations的实例,这里就可以知道,用户程序的open、write等操作最终会调用这里面的函数。
673至677行,创建spidev这一类设备,为后面自动生成设备节点做准备。
679至684行,注册spi设备驱动,spi_register_driver函数的定义在drivers/spi/spi.c中:
00000182 int spi_register_driver(struct spi_driver *sdrv)
00000183 {
00000184 sdrv->driver.bus = &spi_bus_type;
00000185 if (sdrv->probe)
00000186 sdrv->driver.probe = spi_drv_probe;
00000187 if (sdrv->remove)
00000188 sdrv->driver.remove = spi_drv_remove;
00000189 if (sdrv->shutdown)
00000190 sdrv->driver.shutdown = spi_drv_shutdown;
00000191 return driver_register(&sdrv->driver);
00000192 }
184行,该驱动所属的总线。185至190行,一些函数指针的赋值。191行,将驱动注册进设备模型,注册成功的话就会在总线上寻找设备,调用总线上的match函数,看能否与之匹配起来,匹配成功的话,驱动中的probe函数就会被调用。
参数spidev_spi_driver是struct spi_driver的实例,它的定义为:
00000641 static struct spi_driver spidev_spi_driver = {
00000642 .driver = {
00000643 .name = "spidev",
00000644 .owner = THIS_MODULE,
00000645 },
00000646 .probe = spidev_probe,
00000647 .remove = __devexit_p(spidev_remove),
00000648
00000649 /* NOTE: suspend/resume methods are not necessary here.
00000650 * We don't do anything except pass the requests to/from
00000651 * the underlying controller. The refrigerator handles
00000652 * most issues; the controller driver handles the rest.
00000653 */
00000654 };
下面看spidev_probe函数。在drivers/spi/spidev.c中定义的:
00000565 static int __devinit spidev_probe(struct spi_device *spi)
00000566 {
00000567 struct spidev_data *spidev;
00000568 int status;
00000569 unsigned long minor;
00000570
00000571 /* Allocate driver data */
00000572 spidev = kzalloc(sizeof(*spidev), GFP_KERNEL);
00000573 if (!spidev)
00000574 return -ENOMEM;
00000575
00000576 /* Initialize the driver data */
00000577 spidev->spi = spi;
00000578 spin_lock_init(&spidev->spi_lock);
00000579 mutex_init(&spidev->buf_lock);
00000580
00000581 INIT_LIST_HEAD(&spidev->device_entry);
00000582
00000583 /* If we can allocate a minor number, hook up this device.
00000584 * Reusing minors is fine so long as udev or mdev is working.
00000585 */
00000586 mutex_lock(&device_list_lock);
00000587
00000588 minor = find_first_zero_bit(minors, N_SPI_MINORS);
00000589
00000590 if (minor < N_SPI_MINORS) {
00000591 struct device *dev;
00000592
00000593 spidev->devt = MKDEV(SPIDEV_MAJOR, minor);
00000594
00000595 dev = device_create(spidev_class, &spi->dev, spidev->devt,
00000596 spidev, "spidev%d.%d",
00000597 spi->master->bus_num, spi->chip_select);
00000598 status = IS_ERR(dev) ? PTR_ERR(dev) : 0;
00000599 } else {
00000600 dev_dbg(&spi->dev, "no minor number available!\n");
00000601 status = -ENODEV;
00000602 }
00000603 if (status == 0) {
00000604
00000605 set_bit(minor, minors);
00000606
00000607 list_add(&spidev->device_entry, &device_list);
00000608 }
00000609 mutex_unlock(&device_list_lock);
00000610
00000611 if (status == 0)
00000612 spi_set_drvdata(spi, spidev);
00000613 else
00000614 kfree(spidev);
00000615
00000616 return status;
00000617 }
572至574行,分配内存,注意对象的类型是struct spidev_data,看下它在drivers/spi/spidev.c中的定义:
00000075 struct spidev_data {
00000076 dev_t devt;
00000077 spinlock_t spi_lock;
00000078 struct spi_device *spi;
00000079 struct list_head device_entry;
00000080
00000081 /* buffer is NULL unless this device is open (users > 0) */
00000082 struct mutex buf_lock;
00000083 unsigned users;
00000084 u8 *buffer;
00000085 };
76行,设备号。79行,设备链表,所有采用此驱动的设备将连成一个链表。83行,计数,也即是此设备被open的次数。
回到spidev_probe函数,577至586行,一些锁和链表的初始化。588行,从名字上就可以知道,就是找到第一个为0的位,第一个参数minors的定义:
00000054 #define N_SPI_MINORS 32 /* ... up to 256 */
00000055
00000056 static DECLARE_BITMAP(minors, N_SPI_MINORS);
DECLARE_BITMAP是一个宏,定义如下:
#define DECLARE_BITMAP(name,bits) \unsigned long name[BITS_TO_LONGS(bits)]
将宏展开后是这样的,unsigned long minors[1],其实就是定义一个只有一个元素的无符号长整形数组miniors。
590至593行,如果找到了非0位,就将它作为次设备号与之前注册的主设备号生成设备号。
595至598行,创建设备,并生成设备节点,设备节点在/dev目录下,名字的形式为“spidevx.x”。
603至608行,创建设备成功后,将相应的位置1,表示该次设备号已经被使用,同时将该设备加入到设备链表。
611至614行,将设备的私有数据指针指向该设备。
至此,SPI设备驱动的初始化过程也说完了。下面就以应用程序的操作顺序来说,假设是从open-->write这个过程。下面先看驱动中open函数的实现,同样在drivers/spi/spidev.c:
00000477 static int spidev_open(struct inode *inode, struct file *filp)
00000478 {
00000479 struct spidev_data *spidev;
00000480 int status = -ENXIO;
00000481
00000482 mutex_lock(&device_list_lock);
00000483
00000484
00000485 list_for_each_entry(spidev, &device_list, device_entry) {
00000486 if (spidev->devt == inode->i_rdev) {
00000487 status = 0;
00000488 break;
00000489 }
00000490 }
00000491 if (status == 0) {
00000492 if (!spidev->buffer) {
00000493 spidev->buffer = kmalloc(bufsiz, GFP_KERNEL);
00000494 if (!spidev->buffer) {
00000495 dev_dbg(&spidev->spi->dev, "open/ENOMEM\n");
00000496 status = -ENOMEM;
00000497 }
00000498 }
00000499 if (status == 0) {
00000500 spidev->users++;
00000501 filp->private_data = spidev;
00000502 nonseekable_open(inode, filp);
00000503 }
00000504 } else
00000505 pr_debug("spidev: nothing for minor %d\n", iminor(inode));
00000506
00000507 mutex_unlock(&device_list_lock);
00000508 return status;
00000509 }
485至490行,遍历设备链表,每找到一个设备就将它的设备号与打开文件的设备号进行比较,相等的话表示查找成功。
491至505行,查找成功后就分配读写数据内存,使用计数加1,设置文件私有数据指针指向查找到的设备,以后在驱动的write、read函数里就可以把它取出来。
接下来是write函数的定义:
00000190 static ssize_t
00000191 spidev_write(struct file *filp, const char __user *buf,
00000192 size_t count, loff_t *f_pos)
00000193 {
00000194 struct spidev_data *spidev;
00000195 ssize_t status = 0;
00000196 unsigned long missing;
00000197
00000198 /* chipselect only toggles at start or end of operation */
00000199 if (count > bufsiz)
00000200 return -EMSGSIZE;
00000201
00000202 spidev = filp->private_data;
00000203
00000204 mutex_lock(&spidev->buf_lock);
00000205 missing = copy_from_user(spidev->buffer, buf, count);
00000206 if (missing == 0) {
00000207 status = spidev_sync_write(spidev, count);
00000208 } else
00000209 status = -EFAULT;
00000210 mutex_unlock(&spidev->buf_lock);
00000211
00000212 return status;
00000213 }
199至200行,应用程序写入的数据不能大于驱动中缓冲区的大小,默认为4096个字节。
202行,指向文件的私有数据。
205行,拷贝用户空间的数据到内核空间。
207行,spidev_sync_write的定义:
00000130 static inline ssize_t
00000131 spidev_sync_write(struct spidev_data *spidev, size_t len)
00000132 {
00000133 struct spi_transfer t = {
00000134 .tx_buf = spidev->buffer,
00000135 .len = len,
00000136 };
00000137 struct spi_message m;
00000138
00000139 spi_message_init(&m);
00000140 spi_message_add_tail(&t, &m);
00000141 return spidev_sync(spidev, &m);
00000142 }
133行,struct spi_transfer的定义在include/linux/spi/spi.h:
00000427 struct spi_transfer {
00000428 /* it's ok if tx_buf == rx_buf (right?)
00000429 * for MicroWire, one buffer must be null
00000430 * buffers must work with dma_*map_single() calls, unless
00000431 * spi_message.is_dma_mapped reports a pre-existing mapping
00000432 */
00000433 const void *tx_buf;
00000434 void *rx_buf;
00000435 unsigned len;
00000436
00000437 dma_addr_t tx_dma;
00000438 dma_addr_t rx_dma;
00000439
00000440 unsigned cs_change:1;
00000441 u8 bits_per_word;
00000442 u16 delay_usecs;
00000443 u32 speed_hz;
00000444
00000445 struct list_head transfer_list;
00000446 };
433至435行,发送、接收缓冲区和长度。437和438行,发送和接收的DMA地址。
440行,传输完成后是否改变片选信号。
441行,如果为0则使用驱动的默认值。
442行,传输完成后等待多长时间(毫秒)再改变片选信号。
443行,将多个传输连成一个链表。
回到spidev_sync_write函数的137行,在spi.h中定义的struct spi_message:
00000476 struct spi_message {
00000477 struct list_head transfers;
00000478
00000479 struct spi_device *spi;
00000480
00000481 unsigned is_dma_mapped:1;
00000482
00000483 /* REVISIT: we might want a flag affecting the behavior of the
00000484 * last transfer ... allowing things like "read 16 bit length L"
00000485 * immediately followed by "read L bytes". Basically imposing
00000486 * a specific message scheduling algorithm.
00000487 *
00000488 * Some controller drivers (message-at-a-time queue processing)
00000489 * could provide that as their default scheduling algorithm. But
00000490 * others (with multi-message pipelines) could need a flag to
00000491 * tell them about such special cases.
00000492 */
00000493
00000494 /* completion is reported through a callback */
00000495 void (*complete)(void *context);
00000496 void *context;
00000497 unsigned actual_length;
00000498 int status;
00000499
00000500 /* for optional use by whatever driver currently owns the
00000501 * spi_message ... between calls to spi_async and then later
00000502 * complete(), that's the spi_master controller driver.
00000503 */
00000504 struct list_head queue;
00000505 void *state;
00000506 };
477行,一个message可能包含多个transfer,因此用链表将这些transfer连起来。
479行,这次message所使用的spi设备。
481行,是否采用DMA的标志。
495行,传输完成后的回调函数指针。496行,回调函数的参数。
497行,这次message成功传输的字节数。
504和505行,当前驱动拥有的message。
回到spidev_sync_write函数,139行,spi.h中的内联函数spi_message_init:
00000508 static inline void spi_message_init(struct spi_message *m)
00000509 {
00000510 memset(m, 0, sizeof *m);
00000511 INIT_LIST_HEAD(&m->transfers);
00000512 }
很简单,清0内存和初始化message的transfer链表。
140行,spi_message_add_tail也是spi.h中的内联函数:
00000514 static inline void
00000515 spi_message_add_tail(struct spi_transfer *t, struct spi_message *m)
00000516 {
00000517 list_add_tail(&t->transfer_list, &m->transfers);
00000518 }
将transfer加入到链表尾。
141行,spidev_sync函数是在drivers/spi/spidev.c中定义的:
00000105 static ssize_t
00000106 spidev_sync(struct spidev_data *spidev, struct spi_message *message)
00000107 {
00000108 DECLARE_COMPLETION_ONSTACK(done);
00000109 int status;
00000110
00000111 message->complete = spidev_complete;
00000112 message->context = &done;
00000113
00000114 spin_lock_irq(&spidev->spi_lock);
00000115 if (spidev->spi == NULL)
00000116 status = -ESHUTDOWN;
00000117 else
00000118 status = spi_async(spidev->spi, message);
00000119 spin_unlock_irq(&spidev->spi_lock);
00000120
00000121 if (status == 0) {
00000122 wait_for_completion(&done);
00000123 status = message->status;
00000124 if (status == 0)
00000125 status = message->actual_length;
00000126 }
00000127 return status;
00000128 }
108行,定义并初始化一个完成量,完成量是Linux的一种同步机制。
111行,spidev_complete函数里就用来唤醒等待completion,定义如下:
00000100 static void spidev_complete(void *arg)
00000101 {
00000102 complete(arg);
00000103 }
112行,作为spidev_complete函数的参数。
118行,调用drivers/spi/spi.c里的spi_async函数,从函数名知道,这是异步实现的。为什么是异步的?往下看就知道了。
00000737 int spi_async(struct spi_device *spi, struct spi_message *message)
00000738 {
00000739 struct spi_master *master = spi->master;
00000740 int ret;
00000741 unsigned long flags;
00000742
00000743 spin_lock_irqsave(&master->bus_lock_spinlock, flags);
00000744
00000745 if (master->bus_lock_flag)
00000746 ret = -EBUSY;
00000747 else
00000748 ret = __spi_async(spi, message);
00000749
00000750 spin_unlock_irqrestore(&master->bus_lock_spinlock, flags);
00000751
00000752 return ret;
00000753 }
745行,如果master所在的总线被锁住了,那么就返回忙。
748行,看__spi_async函数的定义:
00000679 static int __spi_async(struct spi_device *spi, struct spi_message *message)
00000680 {
00000681 struct spi_master *master = spi->master;
00000682
00000683 /* Half-duplex links include original MicroWire, and ones with
00000684 * only one data pin like SPI_3WIRE (switches direction) or where
00000685 * either MOSI or MISO is missing. They can also be caused by
00000686 * software limitations.
00000687 */
00000688 if ((master->flags & SPI_MASTER_HALF_DUPLEX)
00000689 || (spi->mode & SPI_3WIRE)) {
00000690 struct spi_transfer *xfer;
00000691 unsigned flags = master->flags;
00000692
00000693 list_for_each_entry(xfer, &message->transfers, transfer_list) {
00000694 if (xfer->rx_buf && xfer->tx_buf)
00000695 return -EINVAL;
00000696 if ((flags & SPI_MASTER_NO_TX) && xfer->tx_buf)
00000697 return -EINVAL;
00000698 if ((flags & SPI_MASTER_NO_RX) && xfer->rx_buf)
00000699 return -EINVAL;
00000700 }
00000701 }
00000702
00000703 message->spi = spi;
00000704 message->status = -EINPROGRESS;
00000705 return master->transfer(spi, message);
00000706 }
688至701行,如果master设置了SPI_MASTER_HALF_DUPLEX标志,或者spi设备使用的是3线模式,那么就对message里的每一个transfer的发送和接收buf做一些检查。
705行,调用的是具体的SPI控制器驱动里的函数,这里是drivers/spi/spi_s3c64xx.c里的s3c64xx_spi_transfer函数:
00000763 static int s3c64xx_spi_transfer(struct spi_device *spi,
00000764 struct spi_message *msg)
00000765 {
00000766 struct s3c64xx_spi_driver_data *sdd;
00000767 unsigned long flags;
00000768
00000769 sdd = spi_master_get_devdata(spi->master);
00000770
00000771 spin_lock_irqsave(&sdd->lock, flags);
00000772
00000773 if (sdd->state & SUSPND) {
00000774 spin_unlock_irqrestore(&sdd->lock, flags);
00000775 return -ESHUTDOWN;
00000776 }
00000777
00000778 msg->status = -EINPROGRESS;
00000779 msg->actual_length = 0;
00000780
00000781 list_add_tail(&msg->queue, &sdd->queue);
00000782
00000783 queue_work(sdd->workqueue, &sdd->work);
00000784
00000785 spin_unlock_irqrestore(&sdd->lock, flags);
00000786
00000787 return 0;
00000788 }
781行之前没什么好说的,直接看783行,将work投入到工作队列里,然后就返回,在这里就可以回答之前为什么是异步的问题。以后在某个合适的时间里CPU会执行这个work指定的函数,这里是s3c64xx_spi_work函数,看它的定义:
00000723 static void s3c64xx_spi_work(struct work_struct *work)
00000724 {
00000725 struct s3c64xx_spi_driver_data *sdd = container_of(work,
00000726 struct s3c64xx_spi_driver_data, work);
00000727 unsigned long flags;
00000728
00000729 /* Acquire DMA channels */
00000730 while (!acquire_dma(sdd))
00000731 msleep(10);
00000732
00000733 spin_lock_irqsave(&sdd->lock, flags);
00000734
00000735 while (!list_empty(&sdd->queue)
00000736 && !(sdd->state & SUSPND)) {
00000737
00000738 struct spi_message *msg;
00000739
00000740 msg = container_of(sdd->queue.next, struct spi_message, queue);
00000741
00000742 list_del_init(&msg->queue);
00000743
00000744 /* Set Xfer busy flag */
00000745 sdd->state |= SPIBUSY;
00000746
00000747 spin_unlock_irqrestore(&sdd->lock, flags);
00000748
00000749 handle_msg(sdd, msg);
00000750
00000751 spin_lock_irqsave(&sdd->lock, flags);
00000752
00000753 sdd->state &= ~SPIBUSY;
00000754 }
00000755
00000756 spin_unlock_irqrestore(&sdd->lock, flags);
00000757
00000758 /* Free DMA channels */
00000759 s3c2410_dma_free(sdd->tx_dmach, &s3c64xx_spi_dma_client);
00000760 s3c2410_dma_free(sdd->rx_dmach, &s3c64xx_spi_dma_client);
00000761 }
730行,申请DMA,关于DMA的就不说,一是我对DMA没什么了解,二是这里基本上用不到,后面就知道什么时候才会用到DMA。
735至754行,循环取出队列里的message并调用749行的handle_msg函数进行处理,handle_msg函数的定义如下:
00000568 static void handle_msg(struct s3c64xx_spi_driver_data *sdd,
00000569 struct spi_message *msg)
00000570 {
00000571 struct s3c64xx_spi_info *sci = sdd->cntrlr_info;
00000572 struct spi_device *spi = msg->spi;
00000573 struct s3c64xx_spi_csinfo *cs = spi->controller_data;
00000574 struct spi_transfer *xfer;
00000575 int status = 0, cs_toggle = 0;
00000576 u32 speed;
00000577 u8 bpw;
00000578
00000579 /* If Master's(controller) state differs from that needed by Slave */
00000580 if (sdd->cur_speed != spi->max_speed_hz
00000581 || sdd->cur_mode != spi->mode
00000582 || sdd->cur_bpw != spi->bits_per_word) {
00000583 sdd->cur_bpw = spi->bits_per_word;
00000584 sdd->cur_speed = spi->max_speed_hz;
00000585 sdd->cur_mode = spi->mode;
00000586 s3c64xx_spi_config(sdd);
00000587 }
00000588
00000589 /* Map all the transfers if needed */
00000590 if (s3c64xx_spi_map_mssg(sdd, msg)) {
00000591 dev_err(&spi->dev,
00000592 "Xfer: Unable to map message buffers!\n");
00000593 status = -ENOMEM;
00000594 goto out;
00000595 }
00000596
00000597 /* Configure feedback delay */
00000598 writel(cs->fb_delay & 0x3, sdd->regs + S3C64XX_SPI_FB_CLK);
00000599
00000600 list_for_each_entry(xfer, &msg->transfers, transfer_list) {
00000601
00000602 unsigned long flags;
00000603 int use_dma;
00000604
00000605 INIT_COMPLETION(sdd->xfer_completion);
00000606
00000607 /* Only BPW and Speed may change across transfers */
00000608 bpw = xfer->bits_per_word ? : spi->bits_per_word;
00000609 speed = xfer->speed_hz ? : spi->max_speed_hz;
00000610
00000611 if (bpw != sdd->cur_bpw || speed != sdd->cur_speed) {
00000612 sdd->cur_bpw = bpw;
00000613 sdd->cur_speed = speed;
00000614 s3c64xx_spi_config(sdd);
00000615 }
00000616
00000617 /* Polling method for xfers not bigger than FIFO capacity */
00000618
00000619 if (xfer->len <= ((sci->fifo_lvl_mask >> 1) + 1))
00000620 use_dma = 0;
00000621 else
00000622 use_dma = 1;
00000623
00000624 spin_lock_irqsave(&sdd->lock, flags);
00000625
00000626 /* Pending only which is to be done */
00000627 sdd->state &= ~RXBUSY;
00000628 sdd->state &= ~TXBUSY;
00000629
00000630 enable_datapath(sdd, spi, xfer, use_dma);
00000631
00000632 /* Slave Select */
00000633 enable_cs(sdd, spi);
00000634
00000635 /* Start the signals */
00000636 S3C64XX_SPI_ACT(sdd);
00000637
00000638 spin_unlock_irqrestore(&sdd->lock, flags);
00000639
00000640 status = wait_for_xfer(sdd, xfer, use_dma);
00000641
00000642 /* Quiese the signals */
00000643 S3C64XX_SPI_DEACT(sdd);
00000644
00000645 if (status) {
00000646 dev_err(&spi->dev, "I/O Error: "
00000647 "rx-%d tx-%d res:rx-%c tx-%c len-%d\n",
00000648 xfer->rx_buf ? 1 : 0, xfer->tx_buf ? 1 : 0,
00000649 (sdd->state & RXBUSY) ? 'f' : 'p',
00000650 (sdd->state & TXBUSY) ? 'f' : 'p',
00000651 xfer->len);
00000652
00000653 if (use_dma) {
00000654 if (xfer->tx_buf != NULL
00000655 && (sdd->state & TXBUSY))
00000656 s3c2410_dma_ctrl(sdd->tx_dmach,
00000657 S3C2410_DMAOP_FLUSH);
00000658 if (xfer->rx_buf != NULL
00000659 && (sdd->state & RXBUSY))
00000660 s3c2410_dma_ctrl(sdd->rx_dmach,
00000661 S3C2410_DMAOP_FLUSH);
00000662 }
00000663
00000664 goto out;
00000665 }
00000666
00000667 if (xfer->delay_usecs)
00000668 udelay(xfer->delay_usecs);
00000669
00000670 if (xfer->cs_change) {
00000671 /* Hint that the next mssg is gonna be
00000672 for the same device */
00000673 if (list_is_last(&xfer->transfer_list,
00000674 &msg->transfers))
00000675 cs_toggle = 1;
00000676 else
00000677 disable_cs(sdd, spi);
00000678 }
00000679
00000680 msg->actual_length += xfer->len;
00000681
00000682 flush_fifo(sdd);
00000683 }
00000684
00000685 out:
00000686 if (!cs_toggle || status)
00000687 disable_cs(sdd, spi);
00000688 else
00000689 sdd->tgl_spi = spi;
00000690
00000691 s3c64xx_spi_unmap_mssg(sdd, msg);
00000692
00000693 msg->status = status;
00000694
00000695 if (msg->complete)
00000696 msg->complete(msg->context);
00000697 }
函数很长,580至587行,如果一路走来speed、bpw和mode的值与spi设备的不一致就调用s3c64xx_spi_config函数重新配置,s3c64xx_spi_config函数里面就是对SPI寄存器进行设置的。
590至595行,关于DMA映射的,略过。
598行,设置feedback寄存器。
600行,遍历每一个transfer。605行,又初始化一个完成量,注意这里与之前的那个完成量是不一样的,这里的完成量只有使用DMA传输时才会用得到,接下来很快就可以看到。
608至615行,也是一些关于设置值的检查。
619至622行,只有发送或者接收的数据长度大于fifo的深度(这里是64个字节)设置use_dma为1,也即使用DMA进行传输,否则不使用DMA。
630行,enable_datapath函数的定义为:
00000232 static void enable_datapath(struct s3c64xx_spi_driver_data *sdd,
00000233 struct spi_device *spi,
00000234 struct spi_transfer *xfer, int dma_mode)
00000235 {
00000236 struct s3c64xx_spi_info *sci = sdd->cntrlr_info;
00000237 void __iomem *regs = sdd->regs;
00000238 u32 modecfg, chcfg;
00000239
00000240 modecfg = readl(regs + S3C64XX_SPI_MODE_CFG);
00000241 modecfg&=~(S3C64XX_SPI_MODE_TXDMA_ON|S3C64XX_SPI_MODE_RXDMA_ON);
00000242
00000243 chcfg = readl(regs + S3C64XX_SPI_CH_CFG);
00000244 chcfg &= ~S3C64XX_SPI_CH_TXCH_ON;
00000245
00000246 if (dma_mode) {
00000247 chcfg &= ~S3C64XX_SPI_CH_RXCH_ON;
00000248 } else {
00000249 /* Always shift in data in FIFO, even if xfer is Tx only,
00000250 * this helps setting PCKT_CNT value for generating clocks
00000251 * as exactly needed.
00000252 */
00000253 chcfg |= S3C64XX_SPI_CH_RXCH_ON;
00000254 writel(((xfer->len * 8 / sdd->cur_bpw) & 0xffff)
00000255 | S3C64XX_SPI_PACKET_CNT_EN,
00000256 regs + S3C64XX_SPI_PACKET_CNT);
00000257 }
00000258
00000259 if (xfer->tx_buf != NULL) {
00000260 sdd->state |= TXBUSY;
00000261 chcfg |= S3C64XX_SPI_CH_TXCH_ON;
00000262 if (dma_mode) {
00000263 modecfg |= S3C64XX_SPI_MODE_TXDMA_ON;
00000264 s3c2410_dma_config(sdd->tx_dmach, 1);
00000265 s3c2410_dma_enqueue(sdd->tx_dmach, (void *)sdd,
00000266 xfer->tx_dma, xfer->len);
00000267 s3c2410_dma_ctrl(sdd->tx_dmach, S3C2410_DMAOP_START);
00000268 } else {
00000269 unsigned char *buf = (unsigned char *) xfer->tx_buf;
00000270 int i = 0;
00000271 while (i < xfer->len)
00000272 writeb(buf[i++], regs + S3C64XX_SPI_TX_DATA);
00000273 }
00000274 }
00000275
00000276 if (xfer->rx_buf != NULL) {
00000277 sdd->state |= RXBUSY;
00000278
00000279 if (sci->high_speed && sdd->cur_speed >= 30000000UL
00000280 && !(sdd->cur_mode & SPI_CPHA))
00000281 chcfg |= S3C64XX_SPI_CH_HS_EN;
00000282
00000283 if (dma_mode) {
00000284 modecfg |= S3C64XX_SPI_MODE_RXDMA_ON;
00000285 chcfg |= S3C64XX_SPI_CH_RXCH_ON;
00000286 writel(((xfer->len * 8 / sdd->cur_bpw) & 0xffff)
00000287 | S3C64XX_SPI_PACKET_CNT_EN,
00000288 regs + S3C64XX_SPI_PACKET_CNT);
00000289 s3c2410_dma_config(sdd->rx_dmach, 1);
00000290 s3c2410_dma_enqueue(sdd->rx_dmach, (void *)sdd,
00000291 xfer->rx_dma, xfer->len);
00000292 s3c2410_dma_ctrl(sdd->rx_dmach, S3C2410_DMAOP_START);
00000293 }
00000294 }
00000295
00000296 writel(modecfg, regs + S3C64XX_SPI_MODE_CFG);
00000297 writel(chcfg, regs + S3C64XX_SPI_CH_CFG);
00000298 }
240至244行,读取模式配置和通道配置寄存器。
246至257行,根据是否采用DMA模式设置接收计数寄存器。
259行,很早就为tx_buf分配内存,因此条件成立。因为不考虑DMA模式,因此略过262至268行。
269至272行,循环将发送数据写入到发送寄存器。
276至294行,由于rx_buf为NULL,因此直接略过277至294行。
296、297行,将之前的值写入到寄存器中。
回到handle_msg函数,633行,选中从设备。636行,设置寄存器,开始数据传输。
640行,wait_for_xfer函数的定义:
00000319 static int wait_for_xfer(struct s3c64xx_spi_driver_data *sdd,
00000320 struct spi_transfer *xfer, int dma_mode)
00000321 {
00000322 struct s3c64xx_spi_info *sci = sdd->cntrlr_info;
00000323 void __iomem *regs = sdd->regs;
00000324 unsigned long val;
00000325 int ms;
00000326
00000327 /* millisecs to xfer 'len' bytes @ 'cur_speed' */
00000328 ms = xfer->len * 8 * 1000 / sdd->cur_speed;
00000329 ms += 10; /* some tolerance */
00000330
00000331 if (dma_mode) {
00000332 val = msecs_to_jiffies(ms) + 10;
00000333 val = wait_for_completion_timeout(&sdd->xfer_completion, val);
00000334 } else {
00000335 u32 status;
00000336 val = msecs_to_loops(ms);
00000337 do {
00000338 status = readl(regs + S3C64XX_SPI_STATUS);
00000339 } while (RX_FIFO_LVL(status, sci) < xfer->len && --val);
00000340 }
00000341
00000342 if (!val)
00000343 return -EIO;
00000344
00000345 if (dma_mode) {
00000346 u32 status;
00000347
00000348 /*
00000349 * DmaTx returns after simply writing data in the FIFO,
00000350 * w/o waiting for real transmission on the bus to finish.
00000351 * DmaRx returns only after Dma read data from FIFO which
00000352 * needs bus transmission to finish, so we don't worry if
00000353 * Xfer involved Rx(with or without Tx).
00000354 */
00000355 if (xfer->rx_buf == NULL) {
00000356 val = msecs_to_loops(10);
00000357 status = readl(regs + S3C64XX_SPI_STATUS);
00000358 while ((TX_FIFO_LVL(status, sci)
00000359 || !S3C64XX_SPI_ST_TX_DONE(status, sci))
00000360 && --val) {
00000361 cpu_relax();
00000362 status = readl(regs + S3C64XX_SPI_STATUS);
00000363 }
00000364
00000365 if (!val)
00000366 return -EIO;
00000367 }
00000368 } else {
00000369 unsigned char *buf;
00000370 int i;
00000371
00000372 /* If it was only Tx */
00000373 if (xfer->rx_buf == NULL) {
00000374 sdd->state &= ~TXBUSY;
00000375 return 0;
00000376 }
00000377
00000378 i = 0;
00000379 buf = xfer->rx_buf;
00000380 while (i < xfer->len)
00000381 buf[i++] = readb(regs + S3C64XX_SPI_RX_DATA);
00000382
00000383 sdd->state &= ~RXBUSY;
00000384 }
00000385
00000386 return 0;
00000387 }
328行,根据发送速率计算需要等待的时间。331至334行,与DMA相关的,略过。
335至339行,不断地读状态寄存器,如果接收到的数据长度等于发送数据的长度或超时则退出循环。
342、343行,如果是超时退出循环的,则返回出错。
345至368行,DMA相关的,略过。
369至383行,如果只是发送数据,则直接返回0。否则从接收寄存器里将接收到的数据读出来。
回到handle_msg函数,643行,停止传输。645至665行,如果之前wait_for_xfer函数返回大于0的值,则表示出错,这里就打印一些信息。
667、668行,之前如果有设置延时的话这里就延时。
670至678行,是否需要每个transfer完成都改变片选信号。
680行,累加所有transfer成功发送的数据。
682行,清发送和接收寄存器。
691行,取消DMA映射。
693行,记录状态信息。
695、696行,唤醒之前等待的完成量。
到这里,已经说了整个write过程,不容易啊!。其他的read/ioctl过程是大同小异的。
总结
spidev.c是一个通用的SPI驱动,因此它不处理任何有关具体驱动的逻辑,这就需要在用户空间来完成具体的逻辑。其实这符合了Android驱动的思想,这也是Android HAL层存在的目的:内核驱动只完成硬件操作,具体逻辑放在HAL层,这样就有利于保护厂家、开发者的知识产权。
在用户空间使用ioctl就可以完成write、read操作。
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