linux spi驱动

最近在学习Linux spi驱动，中途出现了诸多疑问，天苍苍野茫茫，坚持总是可以看到牛羊的，本文以新唐NUC972这颗芯片为例进行逐步分析

参考很有价值的两篇文章：
  http://www.th7.cn/system/lin/201507/122488.shtml
  http://blog.chinaunix.net/uid-25445243-id-4026974.html
  
1、SPI 总线注册
  源码路径：drivers/spi/spi.c
  有兴趣的可以看下这位大神的文章，很详细http://blog.chinaunix.net/uid-25445243-id-4032371.html
  
2、spidev.c
  源码路径：drivers/spi/spidev.c
  如果不想写具体的芯片驱动，就可以用kernel自带的驱动spidev.c(这里是困扰我的地方，之前一直没搞明白这里有了
  spi驱动程序，为啥还要编写，因为某个设备对应的驱动必须是唯一的，而驱动却可以对应多个设备),在板级信息spi_board_info
  结构体中将.modalias = "spidev"即可，因为spidev.c中已经驱动取名为“spidev”

3、SPI platform_device设备注册 
  源码路径：arch/arm/mach-nuc970/dev.c
  
  static struct nuc970_spi_info nuc970_spi0_platform_data = {
        .num_cs    = 1,
        .lsb    = 0,
        .txneg    = 1,
        .rxneg    = 0,
        .divider  = 4,
        .sleep    = 0,
        .txnum    = 0,
        .txbitlen  = 8,
        .bus_num  = 0,  //注意这个参数很重要！表示SPI控制器的编号是0，将来在spi从设备的
              //板级信息中有体现，意思是将来这个spi从设备挂在编号为0的spi总线下面；
  };
  
  static struct resource nuc970_spi0_resource[] = {
        [0] = {
                .start = NUC970_PA_SPI0,
                .end   = NUC970_PA_SPI0 + NUC970_SZ_SPI0 - 1,
                .flags = IORESOURCE_MEM,
        },
        [1] = {
                .start = IRQ_SPI0,
                .end   = IRQ_SPI0,
                .flags = IORESOURCE_IRQ,
        }
  };
  
  struct platform_device nuc970_device_spi0 = {
        .name      = "nuc970-spi0",  //设备名
        .id      = -1,
        .num_resources    = ARRAY_SIZE(nuc970_spi0_resource),
        .resource    = nuc970_spi0_resource,
    #if defined(CONFIG_MTD_M25P80) || defined(CONFIG_SPI_SPIDEV)
        .dev    = {
                .platform_data = &nuc970_spi0_platform_data,
    }
    #endif
  };
  
  static struct platform_device *nuc970_public_dev[] __initdata = {
        &nuc970_device_spi0,
  }

  //注册spi设备
  void __init nuc970_platform_init(struct platform_device **device, int size)
  {
    platform_add_devices(device, size);
    platform_add_devices(nuc970_public_dev, ARRAY_SIZE(nuc970_public_dev));
  }

4、SPI platform_driver驱动注册
  源代码路径：drivers/spi/spi-nuc970-p0.c
  
  static struct platform_driver nuc970_spi0_driver = {
    .probe    = nuc970_spi0_probe,  //由于platform_device先于platform_driver注册，所以设
                      //备.name=设备驱动.name时将回调nuc970_spi0_probe
    .remove    = nuc970_spi0_remove,
    .driver    = {
      .name  = "nuc970-spi0",
      .owner  = THIS_MODULE,
    },
  };
  
  //注册spi驱动
  module_platform_driver(nuc970_spi0_driver);

  
5、SPI从设备板级信息 以M25P80 norflash芯片为例
  源码路径：arch/arm/mach-nuc970/dev.c
  
  #if defined(CONFIG_SPI_FLASH_W25Q)
   static struct gsc3280_spi_info w25q_spi1_dev_platdata = {
     .cs_type            = 1,
    .pin_cs            = 87,
    .num_cs            = 1,
    .cs_value            = 0,
    .lsb_flg            = 0,
    .bits_per_word    = 8,
  };
  #endif
  static struct spi_board_info gsc3280_spi_devices[] = {
  #if defined(CONFIG_SPI_FLASH_W25Q)
    {
      .modalias        = "spi-w25q",
      .bus_num        = 0,//注意这个参数很重要（参考第3点解释）！这个从设备将挂在编号为0的总线上，
                //这样从设备“spi-w25q”就与“nuc970-spi0”平台总线（控制器驱动）连接起来了
      .chip_select        = 2,
      .mode            = SPI_MODE_3,
      .max_speed_hz    = 5 * 1000 * 1000,
      .controller_data    = &w25q_spi1_dev_platdata,
    },
  #endif
  };
  
  //注册“spi-w25q”板级信息
  static int __init gsc3280_spi_devices_init(void)
  {
    spi_register_board_info(gsc3280_spi_devices, ARRAY_SIZE(gsc3280_spi_devices));
    return 0;
  }
  device_initcall(gsc3280_spi_devices_init);
  
6、SPI 从设备驱动程序（以字符设备，att7022e就是通过这里进行操作的）
  static struct spi_driver w25q_driver = {
    .driver    = {
      .name    = "spi-w25q",
      .owner    = THIS_MODULE,
    },
    //.id_table    = w25q_ids,
    .probe    = w25q_probe,
    .remove    = __devexit_p(w25q_remove),
  };


  static int __init w25q_init(void)
  {
    return spi_register_driver(&w25q_driver);
  }
  static void __exit w25q_exit(void)
  {
    spi_unregister_driver(&w25q_driver);
  }
  module_init(w25q_init);
  module_exit(w25q_exit);
  
  ......
  
  花了一个三天的时间才搞明白SPI驱动的注册原理。。。