設備樹中的spi設備以及內核對spi節點的處理流程

dts文件中的spi節點

&ecspi2{ /* spi控制器節點 */
    fsl,spi-num-chipselects= < 1 >;
    cs-gpios = <&gpio5 13 0 > ;/* 片選的io口 */
    pinctrl-names = "default";
    pinctrl-0 = <&pinctrl_ecspi2 >;
    status = "okay"; /* status屬性值爲"okay"表示spidev0設備使能, "disabled"表示設備沒有使用*/
    spidev@0x00{
        compatible = "spidev","rohm,dh2228fv";/* 此屬性值用於與spi設備驅動匹配 */
        reg = <0>;  /*spi設備是沒有設備地址的, 這裏是指使用spi控制器的cs-gpios裏的第幾個片選io　*/
        
        spi-max-frequency = <10000000>; /* 指定spi設備的最大工作時鐘 */

    /*以下爲自定義屬性 用於指定工作時序方式及其它功能設置等*/
    ...
    buswidth = <8>; /* 傳輸以8位爲單位 */
    mode = <0>;  /* 使用第幾種工作時序(CPOL, CPHA) */
             /*但在現用的內核源碼裏發現, spi設備的工作時序並不是用mode屬性值來指定的*/
             /* 如CPOL需要設1, 則只需在spi設備節點裏加上"spi-cpol"屬性即可; CPOL設0，則不寫"spi-cpol"屬性即可 */
             /* CPHA設1時，　則在設備節點裏加上"spi-cpha"屬性即可 */

    }; 
};

dtsi文件中的設備樹節點

	ecspi2: ecspi@30830000 {
		compatible = "fsl,imx6ul-ecspi", "fsl,imx51-ecspi";
		reg = <0x0 0x30830000 0x0 0x10000>;
		interrupts = <GIC_SPI 32 IRQ_TYPE_LEVEL_HIGH>;
		clocks = <&clk IMX8MQ_CLK_ECSPI2_ROOT>,
			 <&clk IMX8MQ_CLK_ECSPI2_ROOT>;
		clock-names = "ipg", "per";
		interrupt-parent = <&gpc>;
		status = "disabled";
	};

 

一般帶spi名稱的節點表示spi控制器, 它會先被轉換爲platform_device, 在內核中有對應的platform_driver;（根據compatible屬性來匹配）一般爲廠商所配套的platform_driver文件（freescale的處理文件爲spi-imx.c），platform_driver的probe函數會調用xx_spi_probe, 下面是spi節點在內核中的轉化過程：

spi_imx_probe //drivers/spi/spi-imx.c
    spi_bitbang_start 
      spi_register_master  
        of_register_spi_devices   
            for_each_available_child_of_node(ctlr->dev.of_node, nc) {
                spi = of_register_spi_device(ctlr, nc);  // 讀取設備樹中的spi子節點的屬性 
                                spi = spi_alloc_device(ctlr);                                
                                rc = spi_add_device(spi); //添加spi設備
            }

下面來重點看一下of_register_spi_device()函數，該函數的主要作用是讀取spi節點內的各種值

static struct spi_device *
of_register_spi_device(struct spi_master *master, struct device_node *nc)
{
	struct spi_device *spi;
	int rc;
	u32 value;

	/* Alloc an spi_device 分配一個spi設備*/
	spi = spi_alloc_device(master); 
	if (!spi) {
		dev_err(&master->dev, "spi_device alloc error for %s\n",
			nc->full_name);
		rc = -ENOMEM;
		goto err_out;
	}

	/* Select device driver 獲取 compatibel 屬性 用於匹配spi driver*/ 
	rc = of_modalias_node(nc, spi->modalias,
				sizeof(spi->modalias));
	if (rc < 0) {
		dev_err(&master->dev, "cannot find modalias for %s\n",
			nc->full_name);
		goto err_out;
	}

	/* Device address 獲取 reg 屬性作爲片選編號*/ 
	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);
		goto err_out;
	}
	spi->chip_select = value;

	/* Mode (clock phase/polarity/etc.) spi mode選擇*/
	if (of_find_property(nc, "spi-cpha", NULL))
		spi->mode |= SPI_CPHA;
	if (of_find_property(nc, "spi-cpol", NULL))
		spi->mode |= SPI_CPOL;
	if (of_find_property(nc, "spi-cs-high", NULL))
		spi->mode |= SPI_CS_HIGH;
	if (of_find_property(nc, "spi-3wire", NULL))
		spi->mode |= SPI_3WIRE;
	if (of_find_property(nc, "spi-lsb-first", NULL))
		spi->mode |= SPI_LSB_FIRST;

	/* Device DUAL/QUAD mode */
	if (!of_property_read_u32(nc, "spi-tx-bus-width", &value)) {
		switch (value) {
		case 1:
			break;
		case 2:
			spi->mode |= SPI_TX_DUAL;
			break;
		case 4:
			spi->mode |= SPI_TX_QUAD;
			break;
		default:
			dev_warn(&master->dev,
				"spi-tx-bus-width %d not supported\n",
				value);
			break;
		}
	}

	if (!of_property_read_u32(nc, "spi-rx-bus-width", &value)) {
		switch (value) {
		case 1:
			break;
		case 2:
			spi->mode |= SPI_RX_DUAL;
			break;
		case 4:
			spi->mode |= SPI_RX_QUAD;
			break;
		default:
			dev_warn(&master->dev,
				"spi-rx-bus-width %d not supported\n",
				value);
			break;
		}
	}

	/* Device speed spi速度設置*/
	rc = of_property_read_u32(nc, "spi-max-frequency", &value);
	if (rc) {
		dev_err(&master->dev, "%s has no valid 'spi-max-frequency' property (%d)\n",
			nc->full_name, rc);
		goto err_out;
	}
	spi->max_speed_hz = value;

	/* Store a pointer to the node in the device structure */
	of_node_get(nc); //保存設備樹節點
	spi->dev.of_node = nc;

	/* Register the new device 註冊新的spi設備*/
	rc = spi_add_device(spi);
	if (rc) {
		dev_err(&master->dev, "spi_device register error %s\n",
			nc->full_name);
		goto err_of_node_put;
	}

	return spi;

err_of_node_put:
	of_node_put(nc);
err_out:
	spi_dev_put(spi);
	return ERR_PTR(rc);
}

生成了spi設備之後，會使用spi_match_device()匹配對應的spi driver。匹配成功之後生成對應的spi設備節點。