Touch panel DTS 分析（MSM8994平台，Atmel 芯片）
在MSM8994平台下，Touch panel的DTS节点写在/kernel/arch/arm/boot/dts/qcom/msm8994-mtp.dtsi文件中。具体代码如下：
&soc { i2c@f9924000 { atmel_mxt_ts@4a { compatible = "atmel,atmel_mxt_ts"; reg = <0x4a>; interrupt-parent = <&msm_gpio>; interrupts = <61 0x>; avdd-supply = <&pm8994_l22>; vdd_io-supply = <&pm8994_l14>; ......... }; };
在DTS节点中，我们主要看一下avdd-supply and vdd_io-supply两个属性。这两个属性在C代码里的使用方式如下：
/kernel/drivers/input/touchscreen/atmel_mxt_ts.c mxt_probe_regulators(struct mxt_data *data) { ........ data->reg_vdd_io = regulator_get(dev, "vdd_io"); ........ data->reg_avdd = regulator_get(dev, "avdd"); ........ }
/kernel/drivers/regulator/core.c struct regulator *regulator_get(struct device *dev, const char *id) { return _regulator_get(dev, id, 0); }
static struct regulator *_regulator_get(struct device *dev, const char *id, int exclusive) { ....... rdev = regulator_dev_lookup(dev, id, &ret); if(rdev) goto found; ...... }
static struct regulator_dev *regulator_dev_lookup(struct devic *dev, const char *supply, int *ret) { struct regulator_dev *r; struct device_node *node; ........ /* first do a dt based lookup */ if (dev && dev->of_node) { node = of_get_regulator(dev, supply) if (node) { list_for_each_entry(r, ®ulator_list, list) if ( r->dev.parent && node == r->dev.of_node) return r; ........ } } }
static struct device_node *of_get_regulator(struct device *dev, const char *supply) { struct device_node *regnode = NULL; char prop_name[32]; ....... snprintf(prop_name, 32, "%s-supply", supply); regnode = of_parse_phandle(dev->of_node, prop_name, 0); ........ }
从上述代码大致上可以看到DTS里的vdd_io-supply and avdd-supply属性是如何解析和使用的。在mxt_probe()函数中将字符串“avdd”和“vdd_io”传给regulator_get()函数，一步步调用下来后，在of_get_regulator()函数中将字符串合并成DTS中符合要求的字符串属性，之后通过属性的值来找到相应的regulator_dev 结构体！
