Linux设备驱动 -- TMP75AIDR驱动移植

查看原理图

TMP75AIDR和RK3568采用I2C通信，使用I2C5。

根据TMP75AIDR芯片手册知道I2C地址是由A0 A1 A2决定的。

此原理图芯片I2C地址是0x48。

内核支持

内核中已经有该芯片的驱动支持，使用的是hwmon子系统实现的驱动。

驱动源码位置：kernel/drivers/hwmon/lm75.c

源码文件中定义了支持的设备：

c 复制代码

static const struct of_device_id lm75_of_match[] = {
	{ .compatible = "adi,adt75", .data = (void *)adt75 },
	{ .compatible = "dallas,ds1775", .data = (void *)ds1775 },
	{ .compatible = "dallas,ds75", .data = (void *)ds75 },
	{ .compatible = "dallas,ds7505", .data = (void *)ds7505 },
	{ .compatible = "gmt,g751", .data = (void *)g751 },
	{ .compatible = "national,lm75", .data = (void *)lm75 },
	{ .compatible = "national,lm75a", .data = (void *)lm75a },
	{ .compatible = "national,lm75b", .data = (void *)lm75b },
	{ .compatible = "maxim,max6625", .data = (void *)max6625 },
	{ .compatible = "maxim,max6626", .data = (void *)max6626 },
	{ .compatible = "maxim,mcp980x", .data = (void *)mcp980x },
	{ .compatible = "st,stds75", .data = (void *)stds75 },
	{ .compatible = "microchip,tcn75", .data = (void *)tcn75 },
	{ .compatible = "ti,tmp100", .data = (void *)tmp100 },
	{ .compatible = "ti,tmp101", .data = (void *)tmp101 },
	{ .compatible = "ti,tmp105", .data = (void *)tmp105 },
	{ .compatible = "ti,tmp112", .data = (void *)tmp112 },
	{ .compatible = "ti,tmp175", .data = (void *)tmp175 },
	{ .compatible = "ti,tmp275", .data = (void *)tmp275 },
	{ .compatible = "ti,tmp75", .data = (void *)tmp75 },
	{ .compatible = "ti,tmp75c", .data = (void *)tmp75c },
	{ },
};

驱动通过I2C子系统注册：

c 复制代码

static struct i2c_driver lm75_driver = {
	.class		= I2C_CLASS_HWMON,
	.driver = {
		.name	= "lm75",
		.of_match_table = of_match_ptr(lm75_of_match),
		.pm	= LM75_DEV_PM_OPS,
	},
	.probe		= lm75_probe,
	.id_table	= lm75_ids,
	.detect		= lm75_detect,
	.address_list	= normal_i2c,
};

module_i2c_driver(lm75_driver);

驱动提供的功能：

温度读取（支持9-12位分辨率）
温度上限设置
温度滞后设置
通过hwmon子系统暴露到用户空间
支持设备树自动探测

配置内核使能支持TMP75AIDR

c 复制代码

Device Drivers  --->
	 <*> Hardware Monitoring support  --->
		 <*>   National Semiconductor LM75 and compatibles

内核配置项，确保其值等于y：

复制代码

CONFIG_SENSORS_LM75=y

配置选项定义文件：kernel/drivers/hwmon/Kconfig

编写设备树节点

c 复制代码

&i2c5 {
	...
    ...
    tmp75aidr: tmp75@48 {
        compatible = " ti,tmp75";
		reg = <0x48>;
        status = "okay";
    };
};

compatible属性：值必须为ti,tmp75
reg属性：设备的i2c地址，根据原理图得知其值是0x48。
status值必须是okay，表示已启用。

编写配置好设备树节点，重新编译内核。

用户空间访问

驱动加载后，会在sysfs中生成相应节点，可直接通过如下方式读取温度：

shell 复制代码

root@M3:~# ls /sys/class/hwmon/hwmon0/
device  of_node  subsystem    temp1_max       uevent
name    power    temp1_input  temp1_max_hyst  update_interval

# 查看hwmon设备
ls /sys/class/hwmon/

# 读取温度值
cat /sys/class/hwmon/hwmon0/temp1_input
    temp1_input  temp1_max_hyst  update_interval

# 查看hwmon设备
ls /sys/class/hwmon/

# 读取温度值
cat /sys/class/hwmon/hwmon0/temp1_input