Linux spi驱动分析(一)----总线驱动

一、SPI总线驱动介绍

        SPI总线总共需要四根线，包括MOSI、MISO、CLK和CS。本文首先从SPI设备注册开始来讲述SPI总线驱动。

二、设备注册

        在系统启动的时候，会按照顺序执行一些初始化程序，比如device_initcall和module_init等宏。这些宏是按照顺序执行的，
比如device_initcall的优先级高于module_init，现在我们看下在系统启动的时候注册的spi设备信息。

        程序如下：

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1. /* SPI controller*/
   
2. #if defined(CONFIG_GSC3280_SPI)
   
3. 
   
4. #ifdef CONFIG_SPI1
   
5. static struct resource spi1_resources[]= {
   
6.         [0]= {
   
7.                 .start    = GSC3280_SPI1_BASEADDR& 0x1fffffff,
   
8.                 .end    =(GSC3280_SPI1_BASEADDR & 0x1fffffff)+ 0x54- 1 ,
   
9.                 .flags    = IORESOURCE_MEM,
   
10.         },
    
11.         [1]= {
    
12.                 .start    = EXT_GSC3280_SPI1_IRQ,
    
13.                 .end    = EXT_GSC3280_SPI1_IRQ,
    
14.                 .flags    = IORESOURCE_IRQ,
    
15.         },
    
16. };
    
17. static struct platform_device gsc3280_spi1_device = {
    
18.         .name            ="gsc3280-spi",
    
19.         .id                = 1,
    
20. 
    
21. #ifdef CONFIG_GSC3280_SPI_DMA
    
22.         .dev            ={
    
23.         .dma_mask            =NULL,
    
24.         .coherent_dma_mask    = DMA_BIT_MASK(32),
    
25.         .platform_data        =NULL,
    
26.         },
    
27. #endif
    
28.         .resource        = spi1_resources,
    
29.         .num_resources    = ARRAY_SIZE(spi1_resources),
    
30. };
    
31. #endif
    
32. /* SPI devices*/
    
33. #if defined(CONFIG_SPI_FLASH_W25Q)
    
34.  static struct gsc3280_spi_info w25q_spi1_dev_platdata = {
    
35.     .pin_cs            = 87,
    
36.     .num_cs            = 1,
    
37.     .cs_value            = 0,
    
38.     .lsb_flg            = 0,
    
39.     .bits_per_word    = 8,
    
40. };
    
41. #endif
    
42. static struct spi_board_info gsc3280_spi_devices[]= {
    
43. #if defined(CONFIG_SPI_FLASH_W25Q)
    
44.     {
    
45.         .modalias        ="spi-w25q",
    
46.         .bus_num        = 1,
    
47.         .chip_select        = 3,
    
48.         .mode            = SPI_MODE_3,
    
49.         .max_speed_hz    = 5* 1000 * 1000,
    
50.         .controller_data    =&w25q_spi1_dev_platdata,
    
51.     },
    
52. #endif
    
53. 
    
54. };
    
55. static int __init gsc3280_spi_devices_init(void)
    
56. {
    
57.     spi_register_board_info(gsc3280_spi_devices, ARRAY_SIZE(gsc3280_spi_devices));
    
58.     return 0;
    
59. }
    
60. device_initcall(gsc3280_spi_devices_init);
    
61. #endif    //end #if defined(CONFIG_GSC3280_SPI)

        注意到此处共定义两个设备，使用spi_register_board_info()函数对spi设备进行注册，程序如下：

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1. int __init
   
2. spi_register_board_info(struct spi_board_info const*info, unsigned n)
   
3. {
   
4.     struct boardinfo *bi;
   
5.     int i;
   
6. 
   
7.     bi = kzalloc(n* sizeof(*bi), GFP_KERNEL);
   
8.     if (!bi)
   
9.         return -ENOMEM;
   
10. 
    
11.     for (i= 0; i < n; i++, bi++, info++) {
    
12.         struct spi_master *master;
    
13. 
    
14.         memcpy(&bi->board_info, info,sizeof(*info));
    
15.         mutex_lock(&board_lock);
    
16.         list_add_tail(&bi->list, &board_list);
    
17.         list_for_each_entry(master, &spi_master_list, list)
    
18.             spi_match_master_to_boardinfo(master, &bi->board_info);
    
19.         mutex_unlock(&board_lock);
    
20.     }
    
21. 
    
22.     return 0;
    
23. }

        对于此处，n为1，在程序中首先创建相应的内存，在for循环中，将信息保存到内存中，然后插入board_list链表，接着遍历
spi_master_list链表，注意此处，由于device_initcall的优先级高于module_init，所以此时spi_master_list链表为空，那么还
不能调用spi_match_master_to_boardinfo函数创建spi设备，具体的创建设备将在spi总线驱动的探测函数中，使用spi_register_master()
函数创建设备。

三、总线驱动探测、退出和电源管理函数

3.1、探测函数gsc3280_spi_probe

    程序如下：

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1. static int __init gsc3280_spi_probe(struct platform_device*pdev)
   
2. {
   
3.     int ret = 0;
   
4.     struct gsc3280_spi *gscs;
   
5.     struct spi_master *master;
   
6.     struct resource *mem,*ioarea;
   
7. 
   
8.     DBG("############\n");
   
9.     DBG("gsc3280 spi probe start\n");
   
10.     master = spi_alloc_master(&pdev->dev, sizeof(struct gsc3280_spi));
    
11.     if (!master){
    
12.         ret = -ENOMEM;
    
13.         DBG("!!!!spi_alloc_master error\n");
    
14.         goto exit;
    
15.     }
    
16.     gscs = spi_master_get_devdata(master);
    
17.     memset(gscs, 0, sizeof(struct gsc3280_spi));
    
18.     gscs->master= spi_master_get(master);
    
19.     mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
    
20.     if (!mem){
    
21.         DBG("!!!!no mem resource!\n");
    
22.         ret = -EINVAL;
    
23.         goto err_kfree;
    
24.     }
    
25.     ioarea = request_mem_region(mem->start, resource_size(mem), pdev->name);
    
26.     if (!ioarea){
    
27.         DBG("!!!!SPI region already claimed!\n");
    
28.         ret = -EBUSY;
    
29.         goto err_kfree;
    
30.     }
    
31.     gscs->regs= ioremap_nocache(mem->start, resource_size(mem));
    
32.     if (!gscs->regs){
    
33.         DBG("!!!!SPI ioremap error!\n");
    
34.         ret = -ENOMEM;
    
35.         goto err_release_reg;
    
36.     }
    
37.     DBG("gscs->regs = 0x%p\n", gscs->regs);
    
38.     gscs->irq= platform_get_irq(pdev, 0);
    
39.     if (gscs->irq< 0) {
    
40.         DBG("!!!!no irq resource!\n");
    
41.         ret = gscs->irq;
    
42.         goto err_unmap;
    
43.     }
    
44.     ret = request_irq(gscs->irq, gsc3280_spi_irq, IRQF_DISABLED, dev_name(&pdev->dev), gscs);
    
45.     if (ret< 0) {
    
46.         DBG("!!!!can not get IRQ!\n");
    
47.         goto err_irq;
    
48.     }
    
49.     gscs->clk= clk_get(NULL,"spi1");
    
50.     if (IS_ERR(gscs->clk)){
    
51.         DBG("!!!!failed to find spi1 clock source!\n");
    
52.         ret = PTR_ERR(gscs->clk);
    
53.         goto err_irq;
    
54.     }
    
55.     gscs->max_freq= clk_get_rate(gscs->clk);
    
56.     DBG("rate is %d\n", gscs->max_freq);
    
57.     clk_enable(gscs->clk);
    
58.     gscs->bus_num= pdev->id;
    
59.     gscs->num_cs= 4;
    
60.     gscs->prev_chip= NULL;
    
61.     INIT_LIST_HEAD(&gscs->queue);
    
62.     spin_lock_init(&gscs->slock);
    
63.     
    
64. #ifdef CONFIG_GSC3280_SPI_DMA
    
65.     gscs->dma_priv= pdev->dev.platform_data= &spi_platform_data;
    
66.     if (!gscs->dma_priv)
    
67.         goto err_clk;    //return-ENOMEM;
    
68.     gscs->dma_ops= &gscs_dma_ops;
    
69.     gscs->dma_inited= 0;
    
70.     gscs->dma_addr= (dma_addr_t)(gscs->regs+ 0x24) & 0x1fffffff;
    
71. #endif
    
72. 
    
73.     platform_set_drvdata(pdev, master);
    
74.     master->mode_bits= SPI_CPOL | SPI_CPHA;
    
75.     master->bus_num= gscs->bus_num;
    
76.     master->num_chipselect= gscs->num_cs;
    
77.     master->cleanup= gsc3280_spi_cleanup;
    
78.     master->setup= gsc3280_spi_setup;
    
79.     master->transfer= gsc3280_spi_transfer;
    
80.     gsc3280_spi_hw_init(gscs);
    
81. 
    
82. #ifdef CONFIG_SPI_GSC3280_DMA
    
83.     if (gscs->dma_ops&& gscs->dma_ops->dma_init){
    
84.         ret = gscs->dma_ops->dma_init(gscs);
    
85.         if (ret){
    
86.             dev_warn(&master->dev,"DMA init failed\n");
    
87.             gscs->dma_inited= 0;
    
88.         }
    
89.     }
    
90. #endif
    
91. 
    
92.     ret = gsc3280_init_queue(gscs);
    
93.     if (ret!= 0){
    
94.         DBG("!!!!problem initializing queue!\n");
    
95.         goto err_diable_hw;
    
96.     }
    
97.     ret = gsc3280_start_queue(gscs);
    
98.     if (ret!= 0){
    
99.         DBG("!!!!problem starting queue!\n");
    
100.         goto err_queue_alloc;
     
101.     }
     
102.     ret = spi_register_master(master);
     
103.     if (ret!= 0){
     
104.         DBG("!!!!register spi master error!\n");
     
105.         goto err_queue_alloc;
     
106.     }
     
107.     DBG("gsc3280 spi probe success\n");
     
108.     DBG("############\n");
     
109.     return 0;
     
110. 
     
111. //err_free_master:
     
112.     //spi_master_put(master);
     
113. err_queue_alloc:
     
114.     gsc3280_spi_destroy_queue(gscs);
     
115. #ifdef CONFIG_SPI_GSC3280_DMA
     
116.     if (gscs->dma_ops&& gscs->dma_ops->dma_exit)
     
117.         gscs->dma_ops->dma_exit(gscs);
     
118. #endif
     
119. err_diable_hw:
     
120.     gsc3280_enable_spi(gscs, GSC_SPI_DISABLE);
     
121. //err_clk:
     
122.     clk_disable(gscs->clk);
     
123.     clk_put(gscs->clk);
     
124. err_irq:
     
125.     free_irq(gscs->irq, gscs);
     
126. err_unmap:
     
127.     iounmap(gscs->regs);
     
128. err_release_reg:
     
129.     release_mem_region(mem->start, resource_size(mem));
     
130. err_kfree:
     
131.     kfree(gscs);
     
132.     kfree(master);
     
133. exit:
     
134.     printk(KERN_ERR "!!!!!!gsc3280 probe error!!!!!!\n");
     
135.     return ret;
     
136. }

        说明：

        1) 首先是总线资源的注册，包括申请IO空间和中断。

        2) 接下来注册了中断函数。

        3) 然后注册了spi_master所需要的函数，包括清除、设置和传输等函数，在四中会讲述。

        4) gsc3280_spi_hw_init函数初始化了SPI总线寄存器，接下来讲述。

        5) 总线驱动采用queue机制实现多设备SPI读写，接下来初始化和启动了queue，接下来讲述。

        6) 使用spi_register_master函数注册master，此函数即实现创建了SPI设备结构体，接下来讲述。

        SPI总线寄存器初始化函数gsc3280_spi_hw_init：

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1. /* Restart the controller, disable all interrupts, clean fifo*/
   
2. static void gsc3280_spi_hw_init(struct gsc3280_spi*gscs)
   
3. {
   
4.     gsc3280_enable_spi(gscs, GSC_SPI_DISABLE);
   
5.     gsc3280_spi_mask_intr(gscs, GSC_SPI_SR_MASK);
   
6.     if (!gscs->fifo_len){
   
7.         gscs->fifo_len= 0x10;
   
8.         __raw_writew(0x00, gscs->regs+ GSC_SPI_TXFTLR);
   
9.         __raw_writew(0x00, gscs->regs+ GSC_SPI_RXFTLR);
   
10.     }
    
11.     gsc3280_enable_spi(gscs, GSC_SPI_ENABLE);
    
12. }

        由程序可以看出，此函数首先禁止SPI，屏蔽中断，然后设置fifo深度，最后使能SPI。

        初始化queue函数gsc3280_init_queue：

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1. static int __devinit gsc3280_init_queue(struct gsc3280_spi*gscs)
   
2. {
   
3.     gscs->queue_state= GSC_SPI_QUEUE_STOP;
   
4.     gscs->busy= 0;
   
5.     tasklet_init(&gscs->pump_transfers, gsc3280_spi_pump_transfers,(unsigned long)gscs);
   
6.     INIT_WORK(&gscs->pump_messages, gsc3280_spi_pump_messages);
   
7.     gscs->workqueue= create_singlethread_workqueue(dev_name(gscs->master->dev.parent));
   
8.     if (gscs->workqueue== NULL) {
   
9.         DBG("!!!!create_singlethread_workqueue error!\n");
   
10.         return -EBUSY;
    
11.     }
    
12.     else
    
13.         return 0;
    
14. }

        由程序看出，此函数主要完成初始化队列的作用，包括对queue函数的初始化，最后创建了queue。
        开始queue函数gsc3280_start_queue：

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1. static int gsc3280_start_queue(struct gsc3280_spi*gscs)
   
2. {
   
3.     unsigned long flags;
   
4. 
   
5.     spin_lock_irqsave(&gscs->lock, flags);
   
6.     if ((gscs->run== GSC_SPI_QUEUE_RUN)|| gscs->busy){
   
7.         spin_unlock_irqrestore(&gscs->lock, flags);
   
8.         return -EBUSY;
   
9.     }
   
10.     gscs->run= GSC_SPI_QUEUE_RUN;
    
11.     gscs->cur_msg= NULL;
    
12.     gscs->cur_transfer= NULL;
    
13.     gscs->cur_chip= NULL;
    
14.     gscs->prev_chip= NULL;
    
15.     spin_unlock_irqrestore(&gscs->lock, flags);
    
16.     queue_work(gscs->workqueue,&gscs->pump_messages);
    
17.     return 0;
    
18. }

        此函数首先对queue的状态进行判断，然后初始化相关成员变量，最后调度queue。

        最后看下master注册函数spi_register_master：

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1. int spi_register_master(struct spi_master*master)
   
2. {
   
3.     static atomic_t        dyn_bus_id = ATOMIC_INIT((1<<15)- 1);
   
4.     struct device        *dev = master->dev.parent;
   
5.     struct boardinfo    *bi;
   
6.     int            status = -ENODEV;
   
7.     int            dynamic = 0;
   
8. 
   
9.     if (!dev)
   
10.         return -ENODEV;
    
11. 
    
12.     /* evenif it's just one always-selected device, there must
    
13.      * be at least one chipselect
    
14.      */
    
15.     if (master->num_chipselect== 0)
    
16.         return -EINVAL;
    
17. 
    
18.     /* convention: dynamically assigned bus IDs count down from the max*/
    
19.     if (master->bus_num< 0) {
    
20.         /* FIXME switchto an IDR based scheme, something like
    
21.          * I2C now uses, so we can't run out of"dynamic" IDs
    
22.          */
    
23.         master->bus_num= atomic_dec_return(&dyn_bus_id);
    
24.         dynamic = 1;
    
25.     }
    
26. 
    
27.     spin_lock_init(&master->bus_lock_spinlock);
    
28.     mutex_init(&master->bus_lock_mutex);
    
29.     master->bus_lock_flag= 0;
    
30. 
    
31.     /* register the device,then userspace will see it.
    
32.      * registration fails if the bus ID is in use.
    
33.      */
    
34.     dev_set_name(&master->dev,"spi%u", master->bus_num);
    
35.     status = device_add(&master->dev);
    
36.     if (status< 0)
    
37.         goto done;
    
38.     dev_dbg(dev,"registered master %s%s\n", dev_name(&master->dev),
    
39.             dynamic ? " (dynamic)" : "");
    
40. 
    
41.     mutex_lock(&board_lock);
    
42.     list_add_tail(&master->list,&spi_master_list);
    
43.     list_for_each_entry(bi,&board_list, list)
    
44.         spi_match_master_to_boardinfo(master,&bi->board_info);
    
45.     mutex_unlock(&board_lock);
    
46. 
    
47.     status = 0;
    
48. 
    
49.     /* Register devices from the device tree*/
    
50.     of_register_spi_devices(master);
    
51. done:
    
52.     return status;
    
53. }
    
54. EXPORT_SYMBOL_GPL(spi_register_master);

        说明：

        1) 首先对master成员变量进行检查。

        2) 初始化成员变量。

        3) 将master->list插入到spi_master_list链表中。

        4) 语句list_for_each_entry(bi, &board_list, list)实现遍历board_list链表，在二设备注册中已经讲述了将设备插入到
board_list链表中。此时的board_list链表不为空，已经有相应设备结构体信息了。

        5) 语句spi_match_master_to_boardinfo(master, &bi->board_info);实现设备的创建，函数程序如下：

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1. static void spi_match_master_to_boardinfo(struct spi_master*master,
   
2.                 struct spi_board_info *bi)
   
3. {
   
4.     struct spi_device *dev;
   
5. 
   
6.     if (master->bus_num!= bi->bus_num)
   
7.         return;
   
8. 
   
9.     dev = spi_new_device(master, bi);
   
10.     if (!dev)
    
11.         dev_err(master->dev.parent,"can't create new device for %s\n",
    
12.             bi->modalias);
    
13. }

        说明：

        1) 函数首先判断master的总线号和设备的总线号是否相等，如果不等直接返回。

        2) 函数spi_new_device(master, bi);实现设备创建，如下：

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1. struct spi_device *spi_new_device(struct spi_master*master,
   
2.                  struct spi_board_info *chip)
   
3. {
   
4.     struct spi_device    *proxy;
   
5.     int            status;
   
6. 
   
7.     /* NOTE: caller did any chip->bus_num checks necessary.
   
8.      *
   
9.      * Also, unless we change the return value conventionto use
   
10.      * error-or-pointer(not NULL-or-pointer), troubleshootability
    
11.      * suggests syslogged diagnostics are best here(ugh).
    
12.      */
    
13. 
    
14.     proxy = spi_alloc_device(master);
    
15.     if (!proxy)
    
16.         return NULL;
    
17. 
    
18.     WARN_ON(strlen(chip->modalias)>= sizeof(proxy->modalias));
    
19. 
    
20.     proxy->chip_select= chip->chip_select;
    
21.     proxy->max_speed_hz= chip->max_speed_hz;
    
22.     proxy->mode= chip->mode;
    
23.     proxy->irq= chip->irq;
    
24.     strlcpy(proxy->modalias, chip->modalias, sizeof(proxy->modalias));
    
25.     proxy->dev.platform_data= (void *) chip->platform_data;
    
26.     proxy->controller_data= chip->controller_data;
    
27.     proxy->controller_state= NULL;
    
28. 
    
29.     status = spi_add_device(proxy);
    
30.     if (status< 0) {
    
31.         spi_dev_put(proxy);
    
32.         return NULL;
    
33.     }
    
34. 
    
35.     return proxy;
    
36. }
    
37. EXPORT_SYMBOL_GPL(spi_new_device);
    
38. 
    
39. struct spi_device *spi_alloc_device(struct spi_master*master)
    
40. {
    
41.     struct spi_device    *spi;
    
42.     struct device        *dev = master->dev.parent;
    
43. 
    
44.     if (!spi_master_get(master))
    
45.         return NULL;
    
46. 
    
47.     spi = kzalloc(sizeof*spi, GFP_KERNEL);
    
48.     if (!spi){
    
49.         dev_err(dev,"cannot alloc spi_device\n");
    
50.         spi_master_put(master);
    
51.         return NULL;
    
52.     }
    
53. 
    
54.     spi->master= master;
    
55.     spi->dev.parent= dev;
    
56.     spi->dev.bus= &spi_bus_type;
    
57.     spi->dev.release= spidev_release;
    
58.     device_initialize(&spi->dev);
    
59.     return spi;
    
60. }
    
61. EXPORT_SYMBOL_GPL(spi_alloc_device);

        说明：

        1) 首先调用spi_alloc_device函数创建设备内存，从spi_alloc_device函数中可以看到，首先申请内存，然后对设备程序进行赋值。

        2) 接下来将芯片的信息赋值给设备结构体，包括片选、最大速率、模式、中断和名称等。此处名称尤为重要，在spi设备的注册函数
spi_register_driver中，就是通过名称找到相应的设备信息结构体的。

        3) 程序status = spi_add_device(proxy);实现添加spi设备信息。此函数在--Linux spi驱动分析(二)----spi内核中讲述。

3.2、移除函数gsc3280_spi_remove

        程序如下：

点击(此处)折叠或打开

1. void __exit gsc3280_spi_remove(struct platform_device*pdev)
   
2. {
   
3.     int status = 0;
   
4.     struct spi_master *master = platform_get_drvdata(pdev);
   
5.     struct gsc3280_spi *gscs = spi_master_get_devdata(master);
   
6. 
   
7.     if (!gscs)
   
8.         return;
   
9.     status = gsc3280_spi_destroy_queue(gscs);
   
10.     if (status!= 0)
    
11.         dev_err(&gscs->master->dev,"gsc3280_spi_remove: workqueue will not "
    
12.             "complete, message memory not freed\n");
    
13. 
    
14. #ifdef CONFIG_SPI_GSC3280_DMA
    
15.     if (gscs->dma_ops&& gscs->dma_ops->dma_exit)
    
16.         gscs->dma_ops->dma_exit(gscs);
    
17. #endif
    
18. 
    
19.     gsc3280_enable_spi(gscs, GSC_SPI_DISABLE);
    
20.     free_irq(gscs->irq, gscs);
    
21.     iounmap(gscs->regs);
    
22.     spi_unregister_master(gscs->master);
    
23. }

        说明：

        1) 首先获得总线结构体

        2) 然后删除queue

        3) 最后禁止SPI，释放中断和IO，最后注销master。

3.3、挂起函数gsc3280_spi_suspend

        程序如下：

点击(此处)折叠或打开

1. static int gsc3280_spi_suspend(struct platform_device*pdev, pm_message_t mesg)
   
2. {
   
3.     int ret = 0;
   
4.     struct spi_master *master = platform_get_drvdata(pdev);
   
5.     struct gsc3280_spi *gscs = spi_master_get_devdata(master);
   
6. 
   
7.     ret = gsc3280_spi_stop_queue(gscs);
   
8.     if (ret)
   
9.         return ret;
   
10.     gsc3280_enable_spi(gscs, GSC_SPI_DISABLE);
    
11.     return ret;
    
12. }

        程序中首先停止queue，然后禁止SPI。

        停止queue函数内容如下：

点击(此处)折叠或打开

1. static int gsc3280_spi_stop_queue(struct gsc3280_spi*gscs)
   
2. {
   
3.     int status = 0;
   
4.     unsigned long flags;
   
5.     unsigned limit = 50;
   
6.     
   
7.     spin_lock_irqsave(&gscs->lock, flags);
   
8.     while ((!list_empty(&gscs->queue)|| gscs->busy)&& limit--){
   
9.         spin_unlock_irqrestore(&gscs->lock, flags);
   
10.         msleep(10);
    
11.         spin_lock_irqsave(&gscs->lock, flags);
    
12.     }
    
13.     if (!list_empty(&gscs->queue)|| gscs->busy)
    
14.         status = -EBUSY;
    
15.     else
    
16.         gscs->queue_state= GSC_SPI_QUEUE_STOP;
    
17.     spin_unlock_irqrestore(&gscs->lock, flags);
    
18.     return status;
    
19. }

        程序首先遍历queue链表，查看是否还有queue没有执行，总共尝试50次，如果还有queue没有执行或者设备忙，则错误返回，否
则置正确queue状态。

3.4、恢复函数gsc3280_spi_resume

        程序如下：

点击(此处)折叠或打开

1. static int gsc3280_spi_resume(struct platform_device*pdev)
   
2. {
   
3.     int ret = 0;
   
4.     struct spi_master *master = platform_get_drvdata(pdev);
   
5.     struct gsc3280_spi *gscs = spi_master_get_devdata(master);
   
6. 
   
7.     gsc3280_spi_hw_init(gscs);
   
8.     ret = gsc3280_start_queue(gscs);
   
9.     if (ret)
   
10.         dev_err(&gscs->master->dev,"fail to start queue (%d)\n", ret);
    
11.     return ret;
    
12. }

        程序主要初始化SPI寄存器，然后开始运行queue。

四、spi master支持函数

4.1、清除函数gsc3280_spi_cleanup

点击(此处)折叠或打开

1. static void gsc3280_spi_cleanup(struct spi_device*spi)
   
2. {
   
3.     struct chip_data *chip = spi_get_ctldata(spi);
   
4.     kfree(chip);
   
5. }

        程序首先获取设备指针，然后释放内存。

4.2、设置函数gsc3280_spi_setup

        此函数是一个回调函数，spi核心中的spi_setup()函数会调用此函数，程序如下：

点击(此处)折叠或打开

1. /* This may be called twicefor each spi dev*/
   
2. static int gsc3280_spi_setup(struct spi_device*spi)
   
3. {
   
4.     int ret = 0;
   
5.     struct chip_data *chip = NULL;
   
6.     struct gsc3280_spi_info *chip_info = NULL;
   
7. 
   
8.     DBG("######gsc3280 spi bus setup start######\n");
   
9.     chip = spi_get_ctldata(spi);        /* Only alloc on first setup */
   
10.     if (!chip){
    
11.         chip = kzalloc(sizeof(struct chip_data), GFP_KERNEL);
    
12.         if (!chip){
    
13.             DBG("!!!!kzalloc error!\n");
    
14.             ret = -ENOMEM;
    
15.             goto exit;
    
16.         }
    
17.     }
    
18.     chip_info = spi->controller_data;
    
19.     /* chip_info doesn't always exist*/
    
20.     if (chip_info){
    
21. #ifdef CONFIG_GSC3280_SPI_DMA
    
22.         chip->poll_mode= chip_info->poll_mode;
    
23.         chip->enable_dma= chip_info->enable_dma;
    
24. #endif
    
25.         chip->pin_cs= chip_info->pin_cs;
    
26.         chip->cs_value= chip_info->cs_value;
    
27.         chip->bits_per_word= chip_info->bits_per_word;
    
28.         chip->lsb_flg= chip_info->lsb_flg;
    
29.         gpio_request(chip->pin_cs, spi->modalias);
    
30.         if (chip->cs_value== 0)
    
31.             gpio_direction_output(chip->pin_cs, 1);
    
32.         else
    
33.             gpio_direction_output(chip->pin_cs, 0);
    
34.     }
    
35.     if (spi->bits_per_word== 8){
    
36.         chip->n_bytes= 1;
    
37. #ifdef CONFIG_GSC3280_SPI_DMA
    
38.         chip->dma_width= 1;
    
39. #endif
    
40.     } elseif (spi->bits_per_word== 16){
    
41.         chip->n_bytes= 2;
    
42. #ifdef CONFIG_GSC3280_SPI_DMA
    
43.         chip->dma_width= 2;
    
44. #endif
    
45.     } else{
    
46.         DBG("!!!!spi->bits_per_word = %d error!\n", spi->bits_per_word);
    
47.         ret = -EINVAL;
    
48.         goto exit;
    
49.     }
    
50.     if (!spi->max_speed_hz){
    
51.         DBG("!!!!spi->max_speed_hz = %d, error!\n", spi->max_speed_hz);
    
52.         ret = -EINVAL;
    
53.         goto exit;
    
54.     }
    
55.     chip->speed_hz= spi->max_speed_hz;
    
56.     chip->cr= (chip->lsb_flg<< GSC_SPI_CTL_BITS_NUM)| (spi->mode<< GSC_SPI_CTL_MOD)
    
57.                 | ((chip->bits_per_word- 1) << GSC_SPI_CTL_DSS);
    
58.     spi_set_ctldata(spi, chip);
    
59. 
    
60. exit:
    
61.     if (ret!= 0)
    
62.         DBG("!!!!gsc3280 spi bus setup error!\n");
    
63.     else
    
64.         DBG("######gsc3280 spi bus setup success######\n");
    
65.     return ret;
    
66. }

        说明：

        1) 首先判断参数，如果参数错误，直接返回。

        2) 获取spi控制数据，如果没有，则申请内存创建设备。

        3) 接下来根据实际情况对设备结构体赋值。

4.3、传输函数gsc3280_spi_transfer

        此函数尤为重要，SPI设备传输数据时，就是调用此函数实现数据传输的，此函数主要完成结构体成员变量的
初始化，具体的传输在中断中进行。

点击(此处)折叠或打开

1. /* spi drivercall this function transfer data*/
   
2. static int gsc3280_spi_transfer(struct spi_device*spi, struct spi_message*msg)
   
3. {
   
4.     unsigned long flags = 0;
   
5.     struct gsc3280_spi *gscs = spi_master_get_devdata(spi->master);
   
6. 
   
7.     DBG("####gsc3280 spi transfer start####\n");
   
8.     if (gscs->queue_state== GSC_SPI_QUEUE_STOP){
   
9.         DBG("!!!!queue is stop!\n");
   
10.         return -ESHUTDOWN;
    
11.     }
    
12.     msg->actual_length= 0;
    
13.     msg->status= -EINPROGRESS;
    
14.     msg->state= START_STATE;
    
15.     spin_lock_irqsave(&gscs->slock, flags);
    
16.     list_add_tail(&msg->queue,&gscs->queue);
    
17.     spin_unlock_irqrestore(&gscs->slock, flags);
    
18.     //writel(0x3f,(volatile unsigned int *)(0xbc04a000+ 0x38));    //max divid freq
    
19.     if (gscs->cur_transfer|| gscs->cur_msg){
    
20.         //DBG("gsc3280_spi_transfer: cur transfer or msg not empty\n");
    
21.     } else{
    
22.         //DBG("gsc3280_spi_transfer: no cur transfer and msg\n");
    
23.         queue_work(gscs->workqueue,&gscs->pump_messages);
    
24.     }
    
25.     DBG("####gsc3280 spi transfer success####\n");
    
26.     return 0;
    
27. }

        说明：

        1) 首先判断queue状态，如果是停止状态，则退出。

        2) 对传送结构体成员变量赋值。

        3) 判断当前是否有数据在收发，如果有，就先直接返回。

        4) 如果没有，则调用queue_work()函数，调度函数gsc3280_spi_pump_messages()。程序如下：

点击(此处)折叠或打开

1. /*
   
2.   * when call thisfunction, no msg transfering
   
3.   * deal one msg when call this funciton once.
   
4.   *
   
5.   */
   
6. static void gsc3280_spi_pump_messages(struct work_struct*work)
   
7. {
   
8.     unsigned long flags = 0;
   
9.     struct gsc3280_spi *gscs = container_of(work, struct gsc3280_spi, pump_messages);
   
10. 
    
11.     DBG("####gsc3280_spi_pump_messages####\n");
    
12.     if (list_empty(&gscs->queue)|| (gscs->queue_state== GSC_SPI_QUEUE_STOP)){
    
13.         if (gscs->queue_state== GSC_SPI_QUEUE_STOP)
    
14.             DBG("!!!!queue is stop!\n");
    
15.         else
    
16.             DBG("msg is finished!\n");
    
17.         gscs->busy= 0;
    
18.         return;
    
19.     }
    
20.     
    
21.     spin_lock_irqsave(&gscs->slock, flags);
    
22.     gscs->cur_msg= list_entry(gscs->queue.next, struct spi_message, queue);
    
23.     if (!gscs->cur_msg){
    
24.         spin_unlock_irqrestore(&gscs->slock, flags);
    
25.         DBG("!!!!gsc3280_spi_pump_messages: current no msg!\n");
    
26.         return;
    
27.     }
    
28.     list_del_init(&gscs->cur_msg->queue);
    
29.     gscs->cur_msg->state= RUNNING_STATE;
    
30.     gscs->cur_chip= spi_get_ctldata(gscs->cur_msg->spi);
    
31.     gscs->n_bytes= gscs->cur_chip->n_bytes;
    
32.     gscs->busy= 1;
    
33.     spin_unlock_irqrestore(&gscs->slock, flags);
    
34. 
    
35.     DBG("cs select enable\n");
    
36.     if (gscs->cur_chip->cs_value== 0){
    
37.         gpio_set_value(gscs->cur_chip->pin_cs, 0);
    
38.     }
    
39.     else
    
40.         gpio_set_value(gscs->cur_chip->pin_cs, 1);
    
41.     /* get first transfer */
    
42.     gscs->cur_transfer= list_entry(gscs->cur_msg->transfers.next, struct spi_transfer, transfer_list);
    
43.     if (!gscs->cur_transfer){
    
44.         DBG("!!!!gsc3280_spi_pump_transfers: current no transfer!\n");
    
45.         return;
    
46.     }
    
47.     tasklet_schedule(&gscs->pump_transfers);
    
48.     return;
    
49. }

        说明：

        1) 此函数在两种情况下会被调用：

           a) 当第一次开始SPI传输时，会调用此函数，设置message结构体变量。

            b) 当传输完一个message后，如果判断还有message没有被传输，则调用此函数获取新的message。

        2) 程序首先对变量进行检查，有两种退出情况，第一种是队列已经处于停止状态，第二种是传输msg链表为空。

        3) 上锁，获取新的传输message，如果获取失败，直接解锁退出。

        4) 如果获取msg成功，先删除获取成功msg的链表，然后对SPI总线驱动结构体变量赋初值。
        5) 解锁，使能片选信号CS。
        6) 获取传输的第一个transfer。

        7) 调度gsc3280_spi_pump_transfers函数，函数如下：

点击(此处)折叠或打开

1. /* whencall this function,the cur_msgis the new msg */
   
2. static void gsc3280_spi_pump_transfers(unsigned long data)
   
3. {
   
4.     int clk_div = 0;
   
5.     u32 imask = 0, cr= 0;
   
6.     unsigned long flags = 0;
   
7.     struct spi_transfer *previous = NULL;
   
8.     struct gsc3280_spi *gscs = (struct gsc3280_spi *)data;
   
9. 
   
10.     //DBG("gsc3280_spi_pump_transfers\n");
    
11.     if (gscs->cur_msg->state== ERROR_STATE){
    
12.         DBG("!!!!pump_transfers:cur msg state error!\n");
    
13.         gscs->cur_msg->status= -EIO;
    
14.         goto early_exit;
    
15.     }
    
16.     /* Handleend of message */
    
17.     if (gscs->cur_msg->state== DONE_STATE){
    
18.         gscs->cur_msg->status= 0;
    
19.         goto early_exit;
    
20.     }
    
21.     /* Delayif requested at end of transfer*/
    
22.     if (gscs->cur_msg->state== RUNNING_STATE){
    
23.         previous = list_entry(gscs->cur_transfer->transfer_list.prev, struct spi_transfer, transfer_list);
    
24.         if (previous->delay_usecs)
    
25.             udelay(previous->delay_usecs);
    
26.     }
    
27. 
    
28. #ifdef CONFIG_SPI_GSC3280_DMA
    
29.     gscs->dma_width= gscs->cur_chip->dma_width;
    
30.     gscs->rx_dma= gscs->cur_transfer->rx_dma;
    
31.     gscs->tx_dma= gscs->cur_transfer->tx_dma;
    
32. #endif
    
33. 
    
34.     /* Handle per transfer optionsfor bpw and speed*/
    
35.     if (gscs->cur_transfer->speed_hz){
    
36.         if (gscs->cur_transfer->speed_hz!= gscs->cur_chip->speed_hz){
    
37.             if (gscs->cur_transfer->speed_hz> gscs->max_freq){
    
38.                 printk(KERN_ERR "SPI1: unsupported freq: %dHz\n", gscs->cur_transfer->speed_hz);
    
39.                 gscs->cur_msg->status= -EIO;
    
40.                 return;
    
41.             } else
    
42.                 gscs->cur_chip->speed_hz= gscs->cur_transfer->speed_hz;
    
43.         }
    
44.     }
    
45.     if (gscs->cur_transfer->bits_per_word){
    
46.         switch (gscs->cur_transfer->bits_per_word){
    
47.         case 8:
    
48.         case 16:
    
49.             gscs->n_bytes= gscs->cur_transfer->bits_per_word>> 3;
    
50. #ifdef CONFIG_SPI_GSC3280_DMA
    
51.             gscs->dma_width= gscs->n_bytes;
    
52. #endif
    
53.             break;
    
54.         default:
    
55.             printk(KERN_ERR "SPI1: unsupported bits:" "%db\n", gscs->cur_transfer->bits_per_word);
    
56.             gscs->cur_msg->status= -EIO;
    
57.             return;
    
58.         }
    
59.     }
    
60. 
    
61.     clk_div = gscs->max_freq/ gscs->cur_transfer->speed_hz;
    
62.     clk_div = clk_div / 2 - 1;
    
63.     if (clk_div< 0)
    
64.         clk_div = 0;
    
65.     gscs->cur_chip->clk_div= (u16)clk_div;
    
66. 
    
67.     cr = gscs->cur_chip->cr| GSC_SPI_CTL_EN;
    
68.     writel(cr, gscs->regs+ GSC_SPI_CTRL);    /* enable spi*/
    
69.     writel(gscs->cur_chip->clk_div, gscs->regs+ GSC_SPI_SEABAUR);
    
70.     
    
71.     spin_lock_irqsave(&gscs->slock, flags);
    
72.     //gscs->n_bytes= gscs->cur_chip->n_bytes;
    
73.     gscs->tx= (void *)gscs->cur_transfer->tx_buf;
    
74.     gscs->tx_end= gscs->tx+ gscs->cur_transfer->len;
    
75.     gscs->rx= gscs->cur_transfer->rx_buf;
    
76.     gscs->rx_end= gscs->rx+ gscs->cur_transfer->len;
    
77.     gscs->cs_change= gscs->cur_transfer->cs_change;
    
78.     gscs->len= gscs->cur_transfer->len;
    
79.     spin_unlock_irqrestore(&gscs->slock, flags);
    
80.     
    
81.     imask |= SPI_INT_TX_H_OVER| SPI_INT_RX_L_OVER | SPI_INT_RX_H_OVER | SPI_INT_RX_FULL;
    
82.     if (gscs->tx!= NULL) {
    
83.         imask |= SPI_INT_TX_EMPTY;
    
84.     }
    
85.     gsc3280_spi_umask_intr(gscs, imask);
    
86. 
    
87. #ifdef CONFIG_GSC3280_SPI_DMA
    
88.     /* Checkif current transfer is a DMA transaction */
    
89.     gscs->dma_mapped= map_dma_buffers(gscs);
    
90.     /* Interrupt mode we only needset the TXEI IRQ, as TX/RX always happen syncronizely*/
    
91.     if (!gscs->dma_mapped&& !gscs->cur_chip->poll_mode){
    
92.         //int templen= gscs->len/ gscs->n_bytes;
    
93.         //txint_level= gscs->fifo_len/ 2;
    
94.         //txint_level= (templen > txint_level) ? txint_level : templen;
    
95.     }
    
96.     if (gscs->dma_mapped)
    
97.         gscs->dma_ops->dma_transfer(gscs, cs_change);
    
98.     if (gscs->cur_chip->poll_mode)
    
99.         gsc3280_spi_poll_transfer(gscs);
    
100. #endif
     
101.     
     
102.     return;
     
103.     
     
104. early_exit:
     
105.     gsc3280_spi_giveback(gscs);
     
106.     return;
     
107. }

        说明：

        1) 首先对msg变量进行检测。

        2) 如果变量正确，获取此次传输的分频系数和每次传输几个字节。
        3) 设置SPI控制寄存器和分频寄存器，
        4) 设置SPI总线驱动结构体中的传输或者接收数据指针，打开中断，开始数据传输。

        5) 每传输一个transfer，都会调用此函数一次。

        实际的传输数据在中断中进行，程序如下：

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1. /* thisis transfer message function */
   
2. static irqreturn_t gsc3280_spi_irq(int irq, void*dev_id)
   
3. {
   
4.     struct gsc3280_spi *gscs = dev_id;
   
5.     u32 irq_status = __raw_readw(gscs->regs+ GSC_SPI_ISR);
   
6.     
   
7.     //DBG("gsc3280_spi_irq\n");
   
8.     //DBG("sys_ctl0 = 0x%x\n", readl((volatile unsigned int *)(0xbc04a000+ 0x08)));
   
9.     //DBG("clddiv_spi1 = 0x%x\n", readl((volatile unsigned int *)(0xbc04a000+ 0x38)));
   
10.     //DBG("imux_cfg0 = 0x%x\n", readl((volatile unsigned int *)(0xbc04a000+ 0xb0)));
    
11.     DBG("cr = 0x%x\n", __raw_readw(gscs->regs+ GSC_SPI_CTRL));
    
12.     DBG("imsr = 0x%x, irq_status = 0x%x\n", __raw_readl(gscs->regs+ GSC_SPI_IMSR), irq_status);
    
13. 
    
14.     if (!irq_status) {
    
15.         DBG("!!!!gsc3280_spi_irq: no irq!\n");
    
16.         return IRQ_NONE;
    
17.     }
    
18.     if (!gscs->cur_msg){
    
19.         DBG("!!!!gsc3280_spi_irq: no msg!\n");
    
20.         gsc3280_spi_mask_intr(gscs, SPI_INT_TX_EMPTY| SPI_INT_RX_FULL);
    
21.         return IRQ_HANDLED;
    
22.     }
    
23.     if (irq_status& (SPI_INT_TX_H_OVER| SPI_INT_RX_L_OVER | SPI_INT_RX_H_OVER)){
    
24.         DBG("!!!!gsc3280_spi_irq: fifo overrun/underrun!\n");
    
25.         __raw_writew(0x0e, gscs->regs+ GSC_SPI_ISR);
    
26.         gscs->cur_msg->state= ERROR_STATE;
    
27.         gscs->cur_msg->status= -EIO;
    
28.         queue_work(gscs->workqueue,&gscs->pump_messages);
    
29.         return IRQ_HANDLED;
    
30.     }
    
31.     if (irq_status& SPI_INT_RX_FULL){
    
32.         spi_gsc_read(gscs);
    
33.         return IRQ_HANDLED;
    
34.     }
    
35.     if (irq_status& SPI_INT_TX_EMPTY){
    
36.         spi_gsc_write(gscs);
    
37.     }
    
38.     return IRQ_HANDLED;
    
39. }

        说明：

        1) 首先读取中断状态，如果是空中断，退出中断。

        2) 判断当前是否有msg在传输，如果没有，退出中断。

        3) 判断是否是错误中断，包括溢出等，如果是，屏蔽中断，退出中断。
        4) 如果是接收满中断，则首先接收数据。然后退出中断。

        4) 如果是发送空中断，则发送数据，发送完成后，退出中断。
        现在看下发送数据函数spi_gsc_write()：

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1. static void gsc3280_writer(struct gsc3280_spi*gscs)
   
2. {
   
3.     u16 txw = 0;
   
4.     unsigned long flags = 0;
   
5.     u32 max = gsc3280_spi_tx_max(gscs);
   
6. 
   
7.     //DBG("max = %d, gscs->n_bytes = 0x%x", max, gscs->n_bytes);
   
8.     spin_lock_irqsave(&gscs->slock, flags);
   
9.     while (max--){
   
10.         if (gscs->n_bytes== 1)
    
11.             txw = *(u8 *)(gscs->tx);
    
12.         else
    
13.             txw = *(u16 *)(gscs->tx);
    
14.         DBG("txw = 0x%x\n", txw);
    
15.         writel(txw, gscs->regs+ GSC_SPI_DA_S);
    
16.         gscs->tx+= gscs->n_bytes;
    
17.     }
    
18.     spin_unlock_irqrestore(&gscs->slock, flags);
    
19. }
    
20. static void spi_gsc_write(struct gsc3280_spi*gscs)
    
21. {
    
22.     //DBG("spi_gsc_write\n");
    
23.     gsc3280_spi_mask_intr(gscs, GSC_SPI_SR_MASK);
    
24.     gsc3280_writer(gscs);
    
25.     if (gscs->tx_end== gscs->tx){
    
26.         gsc3280_spi_xfer_done(gscs);
    
27.     }
    
28.     else {
    
29.         gsc3280_spi_umask_intr(gscs, GSC_SPI_SR_MASK);
    
30.     }
    
31. }

        说明：

        1) 首先屏蔽中断。

        2) 发送数据。

        3) 如果发送完成，执行gsc3280_spi_xfer_done(gscs)函数。

        4) 如果没有完成，打开中断，继续发数据。

        对于gsc3280_spi_xfer_done()函数，如下：

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1. static void *gsc3280_spi_next_transfer(struct gsc3280_spi*gscs)
   
2. {
   
3.     struct spi_message *msg = gscs->cur_msg;
   
4.     struct spi_transfer *trans = gscs->cur_transfer;
   
5. 
   
6.     if (trans->transfer_list.next!= &msg->transfers){
   
7.         gscs->cur_transfer= list_entry(trans->transfer_list.next, struct spi_transfer, transfer_list);
   
8.         return RUNNING_STATE;
   
9.     } else
   
10.         return DONE_STATE;
    
11. }
    
12. static void gsc3280_spi_xfer_done(struct gsc3280_spi*gscs)
    
13. {
    
14.     //DBG("gsc3280_spi_xfer_done\n");
    
15.     //DBG("irq_status = 0x%x\n", __raw_readw(gscs->regs+ GSC_SPI_ISR));
    
16.     //DBG("imsr = 0x%x\n", __raw_readl(gscs->regs+ GSC_SPI_IMSR));
    
17.     /* Update total byte transferred return count actual bytes read*/
    
18.     gscs->cur_msg->actual_length+= gscs->len;
    
19.     /* Moveto next transfer*/
    
20.     gscs->cur_msg->state= gsc3280_spi_next_transfer(gscs);
    
21.     if (gscs->cur_msg->state== DONE_STATE){
    
22.         /* Handleend of message */
    
23.         gscs->cur_msg->status= 0;
    
24.         gsc3280_spi_giveback(gscs);
    
25.     } else{
    
26.         tasklet_schedule(&gscs->pump_transfers);
    
27.     }
    

28. }        说明：

        1) 获取下一个transfer，如果还有，则调度gsc3280_spi_pump_transfers()函数准备开始传输。

        2) 如果没有transfer需要传输，调用函数gsc3280_spi_giveback(gscs)，说明此时已经处理完成了一个msg。

        gsc3280_spi_giveback(gscs)函数如下：

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1. /* Caller alreadyset message->status; dmaand pio irqs are blocked */
   
2. static void gsc3280_spi_giveback(struct gsc3280_spi*gscs)
   
3. {
   
4.     unsigned long flags = 0;
   
5. 
   
6.     DBG("gsc3280_spi_giveback\n");
   
7.     //DBG("irq_status = 0x%x\n", readl(gscs->regs+ GSC_SPI_ISR));
   
8.     gsc3280_spi_mask_intr(gscs, GSC_SPI_SR_MASK);
   
9.     DBG("cs select disable\n");
   
10.     if (gscs->cur_chip->cs_value== 0){
    
11.         gpio_set_value(gscs->cur_chip->pin_cs, 1);
    
12.     }
    
13.     else
    
14.         gpio_set_value(gscs->cur_chip->pin_cs, 0);
    
15.     gscs->cur_msg->state= NULL;
    
16.     if (gscs->cur_msg->complete)
    
17.         gscs->cur_msg->complete(gscs->cur_msg->context);
    
18.     
    
19.     spin_lock_irqsave(&gscs->slock, flags);
    
20.     gscs->cur_msg= NULL;
    
21.     gscs->cur_transfer= NULL;
    
22.     gscs->prev_chip= gscs->cur_chip;
    
23.     gscs->cur_chip= NULL;
    
24.     gscs->busy= 0;
    
25. #ifdef CONFIG_SPI_GSC3280_DMA
    
26.     gscs->dma_mapped= 0;
    
27. #endif
    
28.     spin_unlock_irqrestore(&gscs->slock, flags);
    
29.     queue_work(gscs->workqueue,&gscs->pump_messages);
    
30. }

        说明：

        1) 首先屏蔽中断。

        2) 禁止片选。

        3) 设置完成msg。

        4) 上锁，初始化SPI总线结构体变量。

        5) 调用gsc3280_spi_pump_messages()函数，处理下一个msg。

        中断接收数据函数spi_gsc_read(gscs)如下：

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1. static void gsc3280_reader(struct gsc3280_spi*gscs)
   
2. {
   
3.     u16 rxw = 0;
   
4.     unsigned long flags = 0;
   
5.     u32 max = gsc3280_spi_rx_max(gscs);
   
6. 
   
7.     //DBG("max = %d, gscs->n_bytes = 0x%x", max, gscs->n_bytes);
   
8.     spin_lock_irqsave(&gscs->slock, flags);
   
9.     while (max--){
   
10.         rxw = readl(gscs->regs+ GSC_SPI_DA_S);
    
11.         DBG("rxw = 0x%x\n", rxw);
    
12.         if (gscs->n_bytes== 1)
    
13.             *(u8*)(gscs->rx)= (u8)rxw;
    
14.         else
    
15.             *(u16*)(gscs->rx)= rxw;
    
16.         gscs->rx+= gscs->n_bytes;
    
17.     }
    
18.     spin_unlock_irqrestore(&gscs->slock, flags);
    
19. }
    
20. static void spi_gsc_read(struct gsc3280_spi*gscs)
    
21. {
    
22.     //DBG("spi_gsc_read\n");
    
23.     gsc3280_reader(gscs);
    
24.     if (gscs->rx_end== gscs->rx){
    
25.         gsc3280_spi_xfer_done(gscs);
    
26.     }
    
27. }

        说明：

        1) 首先接收数据，如果接收成功，调用gsc3280_spi_xfer_done(gscs);。

        到此，SPI总线驱动就全部讲述完成了，在总线驱动中，使用了queue和tasklet两种机制，queue实现了不同
msg的传输，tasklet实现了msg中不同transfer的传输。

from:http://blog.chinaunix.net/uid-25445243-id-3987576.html