Linux设备驱动剖析之SPI（二）

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 }