SPI子系统分析之四:驱动模块

内核版本:3.9.5

SPI控制器层(平台相关)

上一节讲了SPI核心层的注册和匹配函数,它是平台无关的.正是在核心层抽象了SPI控制器层的相同部分然后提供了统一的API给SPI设备层来使用.我们这一节就能看到,一个SPI控制器以platform_device的形式注册进内核,并且调用spi_register_board_info函数注册了spi_board_info结构.我们前面说过,struct spi_board_info结构是对spi_device的描述,其中的内从最终是要用来初始化struct spi_device实例的.

哎!闲话少说了,越说越糊涂.我们以davinci的dm365平台为例,来看看SPI控制器的相关内容.在arch/arm/mach-davinci/board-dm365-evm.c中有:

 static struct spi_board_info dm365_evm_spi_info[] __initconst = {
     {
         .modalias    = "at25",
         .platform_data    = &at25640,
         .max_speed_hz    =  *  * ,
         .bus_num    = ,
         .chip_select    = ,
         .mode        = SPI_MODE_0,
     },
 };

 static __init void dm365_evm_init(void)
 {
     ……
     dm365_init_spi0(BIT(), dm365_evm_spi_info,
             ARRAY_SIZE(dm365_evm_spi_info));
 }

dm365_evm_init这个函数是dm365平台初始化函数,我略去了和SPI无关的部分.可以看到其中调用了dm365_init_spi0函数,并且将一个struct spi_board_info这个结构类型的数组作为参数传了进去.那么来看看dm365_init_spi0函数,在arch/arm/mach-davinci/dm365.c中:

 static u64 dm365_spi0_dma_mask = DMA_BIT_MASK();

 static struct davinci_spi_platform_data dm365_spi0_pdata = {
     .version     = SPI_VERSION_1,
     .num_chipselect = ,
     .dma_event_q    = EVENTQ_3,
 };

 static struct resource dm365_spi0_resources[] = {
     {
         .start = 0x01c66000,
         .end   = 0x01c667ff,
         .flags = IORESOURCE_MEM,
     },
     {
         .start = IRQ_DM365_SPIINT0_0,
         .flags = IORESOURCE_IRQ,
     },
     {
         .start = ,
         .flags = IORESOURCE_DMA,
     },
     {
         .start = ,
         .flags = IORESOURCE_DMA,
     },
 };

 static struct platform_device dm365_spi0_device = {
     .name = "spi_davinci",/*这个是和platform_driver匹配的依据,具体到davinci的板子就是davinci_spi_driver*/
     .id = ,/*对于SPI,这个值最后会在初始化spi_master的时候用来初始化master->bus_num*/
     .dev = {
         .dma_mask = &dm365_spi0_dma_mask,
         .coherent_dma_mask = DMA_BIT_MASK(),
         .platform_data = &dm365_spi0_pdata,
     },
     .num_resources = ARRAY_SIZE(dm365_spi0_resources),
     .resource = dm365_spi0_resources,
 };

 void __init dm365_init_spi0(unsigned chipselect_mask,
         const struct spi_board_info *info, unsigned len)
 {
     davinci_cfg_reg(DM365_SPI0_SCLK);
     davinci_cfg_reg(DM365_SPI0_SDI);
     davinci_cfg_reg(DM365_SPI0_SDO);

     /* not all slaves will be wired up */
     if (chipselect_mask & BIT())
         davinci_cfg_reg(DM365_SPI0_SDENA0);
     if (chipselect_mask & BIT())
         davinci_cfg_reg(DM365_SPI0_SDENA1);

     spi_register_board_info(info, len);

     platform_device_register(&dm365_spi0_device);
 }

第54行注册了struct spi_board_info实例,就是我们传进来的dm365_evm_spi_info.在设备移植时填充结构体spi_board_info是移植的重要工作.我们来看看这个函数的实现,在drivers/spi/spi.c中:

 int spi_register_board_info(struct spi_board_info const *info, unsigned n)
 {
     struct boardinfo *bi;
     int i;

     bi = kzalloc(n * sizeof(*bi), GFP_KERNEL);/*为结构体boardinfo分配内存空间*/
     if (!bi)
         return -ENOMEM;

     for (i = ; i < n; i++, bi++, info++) {
         struct spi_master *master;

         memcpy(&bi->board_info, info, sizeof(*info));
         mutex_lock(&board_lock);
         list_add_tail(&bi->list, &board_list);/*添加到板级描述符链表*/
         list_for_each_entry(master, &spi_master_list, list)/*将SPI主机控制类链表所有的节点匹配板级信息的设备初始化*/
             spi_match_master_to_boardinfo(master, &bi->board_info);
         mutex_unlock(&board_lock);
     }

     return ;
 }

这里又看到了一个结构struct boardinfo,其实它简单的就像没穿裤子的女人,我们来看,在同文件中:

 struct boardinfo {
     struct list_head    list;
     struct spi_board_info    board_info;
 };

 static LIST_HEAD(board_list);
 static LIST_HEAD(spi_master_list);

 /*
  * Used to protect add/del opertion for board_info list and
  * spi_master list, and their matching process
  */
 /*boardinfo链表操作锁*/
 static DEFINE_MUTEX(board_lock);

这个结构是一个板级相关信息链表,就是说它是一些描述spi_device的信息的集合.结构体boardinfo管理多个结构体spi_board_info,结构体spi_board_info中挂在SPI总线上的设备的平台信息.一个结构体spi_board_info对应着一个SPI设备spi_device.
同时我们也看到了,函数中出现的board_list和spi_master_list都是全局的链表,她们分别记录了系统中所有的boardinfo和所有的spi_master.至于spi_match_master_to_boardinfo函数是什么意思,我们后面还会遇到,到时候再讲.
dm365_init_spi0函数中第56行注册平台设备.我们看到这个platform_device的的name是"spi_davinci",那么就必然还存在一个名为"spi_davinci"的platform_driver.那好办了,搜一下发现在drivers/spi/spi_davinci.c中:

 static struct platform_driver davinci_spi_driver = {
     .driver = {
         .name = "spi_davinci",
         .owner = THIS_MODULE,
         .of_match_table = davinci_spi_of_match,
     },
     .probe = davinci_spi_probe,
     .remove = davinci_spi_remove,
 };
 module_platform_driver(davinci_spi_driver);

Linux设备模型常识告诉我们,当系统中注册了一个名为"spi_davinci"的platform_device时,同时又住了一个名为"spi_davinci"的platform_driver.那么就会执行这里的probe回调.这里我们来看davinci_spi_probe函数.

 static int davinci_spi_probe(struct platform_device *pdev)
 {
     struct spi_master *master;
     struct davinci_spi *dspi;/*davinci_spi这个结构用来描述具体的davinci平台上的spi控制器,等于说是对spi_master的一个封装*/
     struct davinci_spi_platform_data *pdata;
     struct resource *r, *mem;
     resource_size_t dma_rx_chan = SPI_NO_RESOURCE;
     resource_size_t    dma_tx_chan = SPI_NO_RESOURCE;
     int i = , ret = ;
     u32 spipc0;

     /*分配master结构体,其中包括davinci_spi结构的内存空间,使用master.dev.driver_data指向它*/
     master = spi_alloc_master(&pdev->dev, sizeof(struct davinci_spi));
     if (master == NULL) {
         ret = -ENOMEM;
         goto err;
     }

     dev_set_drvdata(&pdev->dev, master);/*pdev->dev.device_private->driver_data = master*/

     dspi = spi_master_get_devdata(master);/*就是获取上文master.dev.driver_data指向的对象地址,其实就是davinci_spi结构对象的空间地址,将
     其赋给dspi*/
     if (dspi == NULL) {/*dspi不能为空哦*/
         ret = -ENOENT;
         goto free_master;
     }

     /*下面这几行就是填充dspi的pdata字段*/
     if (pdev->dev.platform_data) {
         pdata = pdev->dev.platform_data;/*具体到对于dm365来说就是dm365_spi0_pdata*/
         dspi->pdata = *pdata;
     } else {
         /* update dspi pdata with that from the DT */
         ret = spi_davinci_get_pdata(pdev, dspi);
         if (ret < )
             goto free_master;
     }

     /* pdata in dspi is now updated and point pdata to that */
     pdata = &dspi->pdata;/*pdata指针再指向dspi->pdata*/

     r = platform_get_resource(pdev, IORESOURCE_MEM, );/*获取IO资源*/
     if (r == NULL) {
         ret = -ENOENT;
         goto free_master;
     }

     dspi->pbase = r->start;

     mem = request_mem_region(r->start, resource_size(r), pdev->name);/*申请IO内存*/
     if (mem == NULL) {
         ret = -EBUSY;
         goto free_master;
     }

     dspi->base = ioremap(r->start, resource_size(r));/*建立内存映射*/
     if (dspi->base == NULL) {
         ret = -ENOMEM;
         goto release_region;
     }

     dspi->irq = platform_get_irq(pdev, );/*获取irq号*/
     if (dspi->irq <= ) {
         ret = -EINVAL;
         goto unmap_io;
     }

     ret = request_threaded_irq(dspi->irq, davinci_spi_irq, dummy_thread_fn,
                  , dev_name(&pdev->dev), dspi);/*申请spi中断,中断处理函数为davinci_spi_irq*/
     if (ret)
         goto unmap_io;

     /*设置bitbang的所属master*/
     dspi->bitbang.master = spi_master_get(master);
     if (dspi->bitbang.master == NULL) {
         ret = -ENODEV;
         goto irq_free;
     }

     dspi->clk = clk_get(&pdev->dev, NULL);/*获取spi时钟*/
     if (IS_ERR(dspi->clk)) {
         ret = -ENODEV;
         goto put_master;
     }
     clk_prepare_enable(dspi->clk);

     master->dev.of_node = pdev->dev.of_node;
     master->bus_num = pdev->id;/*bus_num*/
     master->num_chipselect = pdata->num_chipselect;/*保存SPI主机控制器支持的片选数量.具体到dm365可以看到dm365_spi0_pdata中将其定义为2*/
     master->setup = davinci_spi_setup;

     /*设置bitbang控制传输的相关函数*/
     dspi->bitbang.chipselect = davinci_spi_chipselect;
     dspi->bitbang.setup_transfer = davinci_spi_setup_transfer;

     dspi->version = pdata->version;/*具体到dm365可以看到dm365_spi0_pdata中将其定义为0*/

     dspi->bitbang.flags = SPI_NO_CS | SPI_LSB_FIRST | SPI_LOOP;
     if (dspi->version == SPI_VERSION_2)
         dspi->bitbang.flags |= SPI_READY;

     r = platform_get_resource(pdev, IORESOURCE_DMA, );/*获取DMA资源,这作为输入缓冲*/
     if (r)
         dma_rx_chan = r->start;
     r = platform_get_resource(pdev, IORESOURCE_DMA, );/*由参数就能知道davinci的DMA资源定义了两个,这里就获取第二个.这作为输出缓冲*/
     if (r)
         dma_tx_chan = r->start;

     dspi->bitbang.txrx_bufs = davinci_spi_bufs;/*传输数据最终要调用的函数*/
     if (dma_rx_chan != SPI_NO_RESOURCE &&
         dma_tx_chan != SPI_NO_RESOURCE) {
         dspi->dma_rx_chnum = dma_rx_chan;
         dspi->dma_tx_chnum = dma_tx_chan;

         ret = davinci_spi_request_dma(dspi);
         if (ret)
             goto free_clk;

         dev_info(&pdev->dev, "DMA: supported\n");
         dev_info(&pdev->dev, "DMA: RX channel: %d, TX channel: %d, "
                 "event queue: %d\n", dma_rx_chan, dma_tx_chan,
                 pdata->dma_event_q);
     }

     dspi->get_rx = davinci_spi_rx_buf_u8;
     dspi->get_tx = davinci_spi_tx_buf_u8;

     init_completion(&dspi->done);/*初始化completion,用于实现同步I/O*/

     /* Reset In/OUT SPI module */
     iowrite32(, dspi->base + SPIGCR0);
     udelay();
     iowrite32(, dspi->base + SPIGCR0);

     /* Set up SPIPC0.  CS and ENA init is done in davinci_spi_setup */
     spipc0 = SPIPC0_DIFUN_MASK | SPIPC0_DOFUN_MASK | SPIPC0_CLKFUN_MASK;
     iowrite32(spipc0, dspi->base + SPIPC0);

     /* initialize chip selects */
     if (pdata->chip_sel) {/*davinci的pdata中chip_sel字段并没有设置,这里为空,因此不会进来*/
         for (i = ; i < pdata->num_chipselect; i++) {
             if (pdata->chip_sel[i] != SPI_INTERN_CS)
                 gpio_direction_output(pdata->chip_sel[i], );
         }
     }

     if (pdata->intr_line)/*dm365这个字段为空*/
         iowrite32(SPI_INTLVL_1, dspi->base + SPILVL);
     else
         iowrite32(SPI_INTLVL_0, dspi->base + SPILVL);

     iowrite32(CS_DEFAULT, dspi->base + SPIDEF);

     /* master mode default */
     set_io_bits(dspi->base + SPIGCR1, SPIGCR1_CLKMOD_MASK);
     set_io_bits(dspi->base + SPIGCR1, SPIGCR1_MASTER_MASK);/*默认设置SPI主控制器工作在master方式*/
     set_io_bits(dspi->base + SPIGCR1, SPIGCR1_POWERDOWN_MASK);

     ret = spi_bitbang_start(&dspi->bitbang);/*注册我们的主机SPI控制器*/
     if (ret)
         goto free_dma;

     dev_info(&pdev->dev, "Controller at 0x%p\n", dspi->base);

     return ret;

 free_dma:
     dma_release_channel(dspi->dma_rx);
     dma_release_channel(dspi->dma_tx);
 free_clk:
     clk_disable_unprepare(dspi->clk);
     clk_put(dspi->clk);
 put_master:
     spi_master_put(master);/*减少引用计数*/
 irq_free:
     free_irq(dspi->irq, dspi);
 unmap_io:
     iounmap(dspi->base);
 release_region:
     release_mem_region(dspi->pbase, resource_size(r));
 free_master:
     kfree(master);
 err:
     return ret;
 }

该函数首先为spi_master结构体以及davinci_spi结构体分配了空间,同时,spi_master.dev.driver_data指向了davinci_spi.接着执行了该条语句:

pdata = pdev->dev.platform_data;/*具体到对于dm365来说就是dm365_spi0_pdata*/

dspi->pdata = *pdata;

NOTE:在这里获取platform_device.dev.platform_data,也就是平台设备的相关数据,这是平台设备移植最需要关注的地方.

随后,为master定义了setup方法,为bitbang定义了3个方法.之后获取了一系列的资源,同时注册了中断服务程序.接着再初始化了completion,这个东东将用于实现同步I/O,他的伟大之处后面会体现出来的.最后调用spi_bitbang_start注册主机控制器.我们来看这个函数,在drivers/spi/spi_bitbang.c中:

 int spi_bitbang_start(struct spi_bitbang *bitbang)
 {
     struct spi_master *master = bitbang->master;
     int status;

     if (!master || !bitbang->chipselect)
         return -EINVAL;

     INIT_WORK(&bitbang->work, bitbang_work);/*初始化一个struct work,处理函数为bitbang_work*/
     spin_lock_init(&bitbang->lock);/*初始化自旋锁*/
     INIT_LIST_HEAD(&bitbang->queue);/*初始化链表头,链表为双向循环链表*/

     if (!master->mode_bits)
         master->mode_bits = SPI_CPOL | SPI_CPHA | bitbang->flags;

     /*检测bitbang中的函数是否都定义了,如果没定义,则默认使用spi_bitbang_xxx*/
     if (!master->transfer)/*master的transfer方法没有定义过*/
         master->transfer = spi_bitbang_transfer;/*使用默认的spi_bitbang_transfe方法*/
     if (!bitbang->txrx_bufs) {/*如果bitbang没有txrx_bufs方法,其实对于davinci在davinci_spi_probe函数中定义过该方法*/
         bitbang->use_dma = ;
         bitbang->txrx_bufs = spi_bitbang_bufs;
         if (!master->setup) {
             if (!bitbang->setup_transfer)
                 bitbang->setup_transfer =
                      spi_bitbang_setup_transfer;
             master->setup = spi_bitbang_setup;
             master->cleanup = spi_bitbang_cleanup;
         }
     } else if (!master->setup)/*对于davinci在davinci_spi_probe函数中定义过该方法*/
         return -EINVAL;
     if (master->transfer == spi_bitbang_transfer &&
             !bitbang->setup_transfer)
         return -EINVAL;

     /* this task is the only thing to touch the SPI bits */
     bitbang->busy = ;
     bitbang->workqueue = create_singlethread_workqueue(
             dev_name(master->dev.parent));/*创建bitbang的工作队列*/
     if (bitbang->workqueue == NULL) {
         status = -EBUSY;
         goto err1;
     }

     /* driver may get busy before register() returns, especially
      * if someone registered boardinfo for devices
      */
     status = spi_register_master(master);/*注册spi控制器*/
     if (status < )
         goto err2;

     return status;

 err2:
     destroy_workqueue(bitbang->workqueue);
 err1:
     return status;
 }
 EXPORT_SYMBOL_GPL(spi_bitbang_start);

定义了控制器的transfer方法为spi_bitbang_transfer.创建了一个工作队列和一个工作bitbang_work,同时创建了一个链表.这些东东后面都会看到.最后,调用了spi_register_master函数,该函数将完成SPI控制器的注册,其中还牵涉到spi_device的注册.我们来看看这个函数.下列函数位于drivers/spi/spi.c:

 int spi_register_master(struct spi_master *master)
 {
     static atomic_t        dyn_bus_id = ATOMIC_INIT((<<) - );
     struct device        *dev = master->dev.parent;
     struct boardinfo    *bi;
     int            status = -ENODEV;
     int            dynamic = ;

     if (!dev)
         return -ENODEV;

     status = of_spi_register_master(master);
     if (status)
         return status;

     /* even if it's just one always-selected device, there must
      * be at least one chipselect
      */
     if (master->num_chipselect == )/*SPI主控制器支持的片选数当然不能为0,否则还怎么挂接从设备啊.一个接口对应一个master,一个master对应
     一条SPI总线,一条总线上可能挂有多个设备,num_chipselect就表示该总线上的设备数*/
         return -EINVAL;

     if ((master->bus_num < ) && master->dev.of_node)
         master->bus_num = of_alias_get_id(master->dev.of_node, "spi");

     /* convention:  dynamically assigned bus IDs count down from the max */
     if (master->bus_num < ) {/*总线号从最大开始减*/
         /* FIXME switch to an IDR based scheme, something like
          * I2C now uses, so we can't run out of "dynamic" IDs
          */
         master->bus_num = atomic_dec_return(&dyn_bus_id);
         dynamic = ;
     }

     spin_lock_init(&master->bus_lock_spinlock);
     mutex_init(&master->bus_lock_mutex);
     master->bus_lock_flag = ;/*这个标志指示SPI总线是否被锁*/

     /* register the device, then userspace will see it.
      * registration fails if the bus ID is in use.
      */
     dev_set_name(&master->dev, "spi%u", master->bus_num);
     status = device_add(&master->dev);/*向内核注册设备*/
     if (status < )
         goto done;
     dev_dbg(dev, "registered master %s%s\n", dev_name(&master->dev),
             dynamic ? " (dynamic)" : "");

     /* If we're using a queued driver, start the queue */
     if (master->transfer)/*对于具体到davinci,此字段在spi_bitbang_start中被初始化为spi_bitbang_transfer*/
         dev_info(dev, "master is unqueued, this is deprecated\n");
     else {
         status = spi_master_initialize_queue(master);
         if (status) {
             device_unregister(&master->dev);
             goto done;
         }
     }

     mutex_lock(&board_lock);
     list_add_tail(&master->list, &spi_master_list);/*把这个SPI主机控制器添加进全局的spi_master_list链表*/
     list_for_each_entry(bi, &board_list, list)/*遍历全局的board_list链表,为每一个boardinfo结构节点查找其中的指向的spi_board_info结构,通过
     对spi_board_info的bus_bum和SPI主机控制器(spi_master)的bus_num进行匹配,来确定SPI从设备是否由此SPI主机控制器来控制.如果匹配,则通
     过调用spi_new_device函数创建spi_device从设备,并且将其注册进内核*/
         spi_match_master_to_boardinfo(master, &bi->board_info);
     mutex_unlock(&board_lock);

     /* Register devices from the device tree and ACPI */
     of_register_spi_devices(master);
     acpi_register_spi_devices(master);
 done:
     return status;
 }
 EXPORT_SYMBOL_GPL(spi_register_master);

该函数注释一目了然,我们来看看spi_match_master_to_boardinfo这个函数吧.在同文件中有:

 /*使用SPI主控制类和板级信息匹配则添加一个新设备*/
 static void spi_match_master_to_boardinfo(struct spi_master *master,
                 struct spi_board_info *bi)
 {
     struct spi_device *dev;

     if (master->bus_num != bi->bus_num)/*通过bus_num对spi设备和master进行匹配*/
         return;

     dev = spi_new_device(master, bi);/*执行到此,表示匹配完成,SPI设备由该SPI接口来控制,开始创建spi_device*/
     if (!dev)
         dev_err(master->dev.parent, "can't create new device for %s\n",
             bi->modalias);
 }

地球人都知道这段代码什么意思,好了继续看spi_new_device函数.在同文件中:

 struct spi_device *spi_new_device(struct spi_master *master,
                   struct spi_board_info *chip)
 {
     struct spi_device    *proxy;
     int            status;

     /* NOTE:  caller did any chip->bus_num checks necessary.
      *
      * Also, unless we change the return value convention to use
      * error-or-pointer (not NULL-or-pointer), troubleshootability
      * suggests syslogged diagnostics are best here (ugh).
      */

     proxy = spi_alloc_device(master);/*分配spi_device结构,并初始化一些字段*/
     if (!proxy)
         return NULL;

     WARN_ON(strlen(chip->modalias) >= sizeof(proxy->modalias));

     /*从spi_board_info获取SPI从设备的参数*/
     proxy->chip_select = chip->chip_select;
     proxy->max_speed_hz = chip->max_speed_hz;
     proxy->mode = chip->mode;
     proxy->irq = chip->irq;
     strlcpy(proxy->modalias, chip->modalias, sizeof(proxy->modalias));
     proxy->dev.platform_data = (void *) chip->platform_data;
     proxy->controller_data = chip->controller_data;
     proxy->controller_state = NULL;

     status = spi_add_device(proxy);/*将新设备添加进内核*/
     if (status < ) {
         spi_dev_put(proxy);/*从内核模块中撤销这个SPI(从)设备,但是这貌似并没有释放spi_alloc_device开辟的内存.实质上这个函数只是减少
     了SPI(从)设备的引用计数*/
         return NULL;
     }

     return proxy;
 }
 EXPORT_SYMBOL_GPL(spi_new_device);

这个函数首先创建了spi_device结构,让后通过板级信息spi_board_info将SPI从设备的相关信息复制给spi_device结构,从而完成了spi_device结构的定义,最后调用spi_add_device,完成spi_device的注册.其中struct spi_board_info *chip这就是我们当初arch/arm/mach-davinci/board-dm365-evm.c中定义的dm365_evm_spi_info数组中的结构实例.

第25行我们就知道,这里注册的spi_device的modalias字段就被初始化为"at25".那么与其对应的spi_driver的device_driver中的name字段肯定为"at25".只有这样才能在SPI核心层的spi_match_device函数中匹配.搜了一遍内核,看到在drivers/msic/eeprom/at25.c中有:

 static struct spi_driver at25_driver = {
     .driver = {
         .name        = "at25",
         .owner        = THIS_MODULE,
     },
     .probe        = at25_probe,/*与相应的SPI(从)设备spi_device匹配成功后,则调用这里的probe函数*/
     .remove        = at25_remove,
 };

 module_spi_driver(at25_driver);

第10行这个宏是SPI架构专门定义的,在include/linux/spi/spi.h中,我们来看:

 #define module_spi_driver(__spi_driver) \
     module_driver(__spi_driver, spi_register_driver, \
             spi_unregister_driver)

让暴风雨来的更猛烈些吧,研究内核的孩纸都伤不起啊,我们只有硬着头皮往下看,在include/linux/device.h中:

 #define module_driver(__driver, __register, __unregister, ...) \
 static int __init __driver##_init(void) \
 { \
     return __register(&(__driver) , ##__VA_ARGS__); \
 } \
 module_init(__driver##_init); \
 static void __exit __driver##_exit(void) \
 { \
     __unregister(&(__driver) , ##__VA_ARGS__); \
 } \
 module_exit(__driver##_exit);

山重水复疑无路,柳暗花明又一村.这东东你让我说啥~没说的.相信大家也不想在听我唠叨.但是这里为什么多此一举写了这么一个叫宏,而不是像其他的linux模块那样直接写两个module_xxx呢?这是因为这个设备eeprom本身是不可插拔的,也就不需要什么加载卸载的过程,系统上电运行直接就注册了.
那么我们知道了,现在因为SPI子系统核心层我们已经注册了一条SPI总线,就是spi_bus_type.它里面的match回调函数我们已经看过了,就是spi_match_device.就是在这个函数中将完成这个spi_device和spi_driver的匹配,匹配成功就会去执行spi_driver的probe回调了.我们来看,at25_probe函数在drivers/msic/eeprom/at25.c中:

 static int at25_probe(struct spi_device *spi)
 {
     struct at25_data    *at25 = NULL;/*这个结构其实就是对spi_device的封装,我们可以像理解面向对象那样将这个结构理解为对spi_device的实例*/
     struct spi_eeprom    chip;/*此结构用来作为记录一个SPI EEPROMS的句柄,它保存了platform_data的数据*/
     struct device_node    *np = spi->dev.of_node;
     int            err;
     int            sr;
     int            addrlen;

     /* Chip description */
     if (!spi->dev.platform_data) {/*具体到dm365平台,此platform_data就是arch/arm/mach-davinci/board-ddm365-evm.c中定义的的at25640*/
         if (np) {
             err = at25_np_to_chip(&spi->dev, np, &chip);
             if (err)
                 goto fail;
         } else {
             dev_err(&spi->dev, "Error: no chip description\n");
             err = -ENODEV;
             goto fail;
         }
     } else
         chip = *(struct spi_eeprom *)spi->dev.platform_data;

     /* For now we only support 8/16/24 bit addressing */
     if (chip.flags & EE_ADDR1)/*flags用来标志eeprom的位宽和读写模式,具体到dm365平台此flags为EE_ADDR2*/
         addrlen = ;
     else if (chip.flags & EE_ADDR2)
         addrlen = ;
     else if (chip.flags & EE_ADDR3)
         addrlen = ;
     else {
         dev_dbg(&spi->dev, "unsupported address type\n");
         err = -EINVAL;
         goto fail;
     }

     /* Ping the chip ... the status register is pretty portable,
      * unlike probing manufacturer IDs.  We do expect that system
      * firmware didn't write it in the past few milliseconds!
      */
     /*ping一下芯片,状态寄存器是很容易被检测的,不像制造商ID那样麻烦.我们期待系统固件之前没有写入它.*/
     sr = spi_w8r8(spi, AT25_RDSR);/*同步的读取状态寄存器的值,返回的八位数据保存在sr中.spi_w8r8这个函数有可能会睡眠*/
     if (sr <  || sr & AT25_SR_nRDY) {
         dev_dbg(&spi->dev, "rdsr --> %d (%02x)\n", sr, sr);
         err = -ENXIO;
         goto fail;
     }

     if (!(at25 = kzalloc(sizeof *at25, GFP_KERNEL))) {/*以kmalloc分配内存,并清0*/
         err = -ENOMEM;
         goto fail;
     }

     mutex_init(&at25->lock);/*初始化互斥体*/
     at25->chip = chip;/*记录下spi_eeprom*/
     at25->spi = spi_dev_get(spi);/*记录下这个片子对应的spi_device*/
     dev_set_drvdata(&spi->dev, at25);/*spi->dev.device_private->driver_data = at25*/
     at25->addrlen = addrlen;/*我觉得应该可以理解为这个片子使用的位宽是多少个字节.那根据上文分析,此处值为2*/

     /* Export the EEPROM bytes through sysfs, since that's convenient.
      * And maybe to other kernel code; it might hold a board's Ethernet
      * address, or board-specific calibration data generated on the
      * manufacturing floor.
      *
      * Default to root-only access to the data; EEPROMs often hold data
      * that's sensitive for read and/or write, like ethernet addresses,
      * security codes, board-specific manufacturing calibrations, etc.
      */
     /*通过sysfs文件系统导出EEPROM的字节,因为这是很方便的.也许其他内核代码也是这样做的:比如保存板子的以太网地址,或者是生产商的特定板的校验数据.
     默认只有root用户能够访问的数据.EEPROMs经常保存一些敏感的读或写的数据,像是以太网地址,安全码,特定板的校准数据等*/
     sysfs_bin_attr_init(&at25->bin);/*初始化一个动态分配的bin_attribute属性*/
     at25->bin.attr.name = "eeprom";/*属性的名字*/
     at25->bin.attr.mode = S_IRUSR;/*属性的模式(用户可读)*/
     at25->bin.read = at25_bin_read;/*属性的读方法*/
     at25->mem.read = at25_mem_read;/*片子的内存读函数*/

     at25->bin.size = at25->chip.byte_len;
     if (!(chip.flags & EE_READONLY)) {/*flags用来标志eeprom的位宽和读写模式,具体到dm365平台此flags为EE_ADDR2*/
         at25->bin.write = at25_bin_write;/*如果eeprom片子不是只读的话,那么就设置属性的写方法*/
         at25->bin.attr.mode |= S_IWUSR;/*增加属性的模式(用户可写)*/
         at25->mem.write = at25_mem_write;/*片子的内存写函数*/
     }

     err = sysfs_create_bin_file(&spi->dev.kobj, &at25->bin);/*创建一个二进制的属性文件*/
     if (err)
         goto fail;

     if (chip.setup)/*如果片子定义了setup函数,具体到dm365平台,此platform_data就是arch/arm/mach-davinci/board-ddm365-evm.c中定义的的at25640里并没有
     定义这个函数,因此为空*/
         chip.setup(&at25->mem, chip.context);/*使用片子的setup函数做一些初始化*/

     dev_info(&spi->dev, "%Zd %s %s eeprom%s, pagesize %u\n",
         (at25->bin.size < )
             ? at25->bin.size
             : (at25->bin.size / ),
         (at25->bin.size < ) ? "Byte" : "KByte",
         at25->chip.name,
         (chip.flags & EE_READONLY) ? " (readonly)" : "",
         at25->chip.page_size);
     return ;
 fail:
     dev_dbg(&spi->dev, "probe err %d\n", err);
     kfree(at25);
     return err;
 }

根据代码就能知道,这个spi_device实际上对应的是一个eeprom,而这里就是它的操作的一些初始化.也就是说,对于分析的这个davinci代码的实例,是dm365平台的,其开发板上应该是将eeprom通过spi总线挂接在了spi_master上.也就是挂接在了SOC上,因为我们的dm365片子本身就集成了spi_master.之后要访问eeprom其实回调最终的都是这里提供的一些接口.听起来有点黏糊,看个图吧:

哎,就写到这里,本人不会用visio,画个这图画了一下午~丢人啊!