轉自http://blog.csdn.net/yaolanshu_june/article/details/52152790

本文主要驗證kernel/Documentation/spi目錄下spidev_test.c的測試例程，能否正?？刂芐PI接口。

一、驅動配置1.修改設備樹找到內核源碼的linux-imx_share/arch/arm/boot/dts目錄下的imx6qdl-sabresd.dtsi，找到ecspi1的代碼

將spidev這段注釋去掉，開啟這段代碼。

2.修改內核配置輸入:make ARCH=arm menuconfig進行內核配置，進入配置界面，依次選擇Device Drivers->SPI support，使User mode SPI device driver support選項起作用，選擇Y，并save。

選擇這個的目的是使spidev.c參與編譯，原因可以參考linux-imx_share/drivers/spi目錄下的Kconfig和Makefile。

配置好之后，運行./build.sh，編譯生成zImage，zImage-imx6dl-sabresd-emmc.dtb燒寫進板子。檢查新燒進去的系統里，dev目錄下有無spidev32766.0。如有，表示spidev的設備驅動燒寫成功。

二、測試1.找到ECSPI的引腳，連接MISO和MOSI，進行自回環測試。

2.編寫makefile生成自測代碼spidev_test.c對應的可執行程序。

 使用rz命令，將spidev_test上載至板子

接收的數據正確，自回環測試成功。------------------------------------------------------------------------------------------------------------------------------------疑問：生成的設備節點為什么是spidev32766.0？

在spidev.c中的函數spidev_PRobe里，找到設備節點的賦值。[objc] view plain copy print?spidev->devt = MKDEV(SPIDEV_MAJOR, minor);  //計算出設備號  //創建設備/dev/spidev%d.%d(spidev總線號.片選號)  dev = device_create(spidev_class, &spi->dev, spidev->devt,              spidev, "spidev%d.%d",              spi->master->bus_num, spi->chip_select);  下面看下spi->master->bus_num和spi->chip_select的值。

在drivers/spi目錄下的spi.c文件中，spi_alloc_master函數中，給master->bus_num = -1進行了初始化。[objc] view plain copy print?struct spi_master *spi_alloc_master(struct device *dev, unsigned size)  {      struct spi_master   *master;        if (!dev)          return NULL;        master = kzalloc(size + sizeof(*master), GFP_KERNEL);      if (!master)          return NULL;        device_initialize(&master->dev);      <span style="color:#3333ff;">master->bus_num = -1;  //初始化      <span style="color:#3333ff;">master->num_chipselect = 1;      master->dev.class = &spi_master_class;      master->dev.parent = get_device(dev);      spi_master_set_devdata(master, &master[1]);        return master;  }  在spi_register_master函數中，對bus_num進行了處理[objc] view plain copy print?/* convention:  dynamically assigned bus IDs count down from the max */      if (master->bus_num < 0) <span style="font-family: Arial, Helvetica, sans-serif;">{</span> [objc] view plain copy print?/* 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 = 1; 

其中dyn_bus_id計算結果是32767[objc] view plain copy print?static atomic_t     dyn_bus_id = ATOMIC_INIT((1<<15) - 1);  [objc] view plain copy print?#define atomic_dec_return(v)    (atomic_sub_return(1, v))  [objc] view plain copy print?static inline int atomic_sub_return(int i, atomic_t *v)  {      unsigned long flags;      int val;        raw_local_irq_save(flags);      val = v->counter;      v->counter = val -= i;      raw_local_irq_restore(flags);        return val;  }  如此計算出master->bus_num=32766。of_register_spi_devices函數里chip_select的獲得是通過value賦值的,而value是通過設備樹里的reg后面的值取得的[objc] view plain copy print?/* Device address */          rc = of_property_read_u32(nc, "reg", &value);          if (rc) {              dev_err(&master->dev, "%s has no valid 'reg' property (%d)/n",                  nc->full_name, rc);              spi_dev_put(spi);              continue;          }          spi->chip_select = value;  [objc] view plain copy print?spidev: spidev@0 {          spi-max-frequency = <24000000>;            reg = <0>;            compatible = "rohm,dh2228fv";             };  所以生成的設備節點號是spidev32766.0。

如果在imx6qdl-sabresd.dtsi設備樹里，改成下面這樣，則生成的設備節點號是spidev32766.1。[plain] view plain copy print?&ecspi1 {      fsl,spi-num-chipselects = <2>; //改成2      cs-gpios = <&gpio2 30 0>;      pinctrl-names = "default";      pinctrl-0 = <&pinctrl_ecspi1_1>;      status = "okay";        Flash: m25p32@0 {          #address-cells = <1>;          #size-cells = <1>;          compatible = "winbond,w25q32";          spi-max-frequency = <20000000>;          reg = <0>;      };        spidev: spidev@1 {          spi-max-frequency = <24000000>;            reg = <1>;            compatible = "rohm,dh2228fv";             };    };