最近在學習Linux spi驅動，中途出現了諸多疑問，天蒼蒼野茫茫，堅持總是可以看到牛羊的，本文以新唐NUC972這顆晶片為例進行逐步分析

參考很有價值的兩篇文章：
	http://www.th7.cn/system/lin/201507/122488.shtml
	http://blog.chinaunix.net/uid-25445243-id-4026974.html
	
1、SPI 匯流排註冊
	原始碼路徑：drivers/spi/spi.c
	有興趣的可以看下這位大神的文章，很詳細http://blog.chinaunix.net/uid-25445243-id-4032371.html
	
2、spidev.c
	原始碼路徑：drivers/spi/spidev.c
	如果不想寫具體的晶片驅動，就可以用kernel自帶的驅動spidev.c(這裡是困擾我的地方，之前一直沒搞明白這裡有了
	spi驅動程式，為啥還要編寫，因為某個裝置對應的驅動必須是唯一的，而驅動卻可以對應多個裝置),在板級資訊spi_board_info
	結構體中將.modalias = "spidev"即可，因為spidev.c中已經驅動取名為“spidev”

3、SPI platform_device設備註冊 
	原始碼路徑：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,	//注意這個引數很重要！表示SPI控制器的編號是0，將來在spi從裝置的
							//板級資訊中有體現，意思是將來這個spi從裝置掛在編號為0的spi匯流排下面；
	};
	
	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",	//裝置名
        .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,
	}

	//註冊spi裝置
	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驅動註冊
	原始碼路徑：drivers/spi/spi-nuc970-p0.c
	
	static struct platform_driver nuc970_spi0_driver = {
		.probe		= nuc970_spi0_probe,	//由於platform_device先於platform_driver註冊，所以設
											//備.name=裝置驅動.name時將回調nuc970_spi0_probe
		.remove		= nuc970_spi0_remove,
		.driver		= {
			.name	= "nuc970-spi0",
			.owner	= THIS_MODULE,
		},
	};
	
	//註冊spi驅動
	module_platform_driver(nuc970_spi0_driver);

	
5、SPI從裝置板級資訊 以M25P80 norflash晶片為例
	原始碼路徑：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,//注意這個引數很重要（參考第3點解釋）！這個從裝置將掛在編號為0的總線上，
								//這樣從裝置“spi-w25q”就與“nuc970-spi0”平臺匯流排（控制器驅動）連線起來了
			.chip_select        = 2,
			.mode            = SPI_MODE_3,
			.max_speed_hz    = 5 * 1000 * 1000,
			.controller_data    = &w25q_spi1_dev_platdata,
		},
	#endif
	};
	
	//註冊“spi-w25q”板級資訊
	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 從裝置驅動程式（以字元裝置，att7022e就是通過這裡進行操作的）
	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);
	
	......
	
	花了一個三天的時間才搞明白SPI驅動的註冊原理。。。