GPIO 使用

简介

GPIO, 全称 General-Purpose Input/Output(通用输入输出),是一种软件运行期间能够动态配置和控制的通用引脚。

AIO-3288C 有 9 组 GPIO bank: GPIO0,GPIO1, …, GPIO8。每组又以 A0~A7, B0~B7, C0~C7, D0~D7 作为编号区分。 每个 GPIO 口除了通用输入输出功能外,还可能有其它复用功能,例如 GPIO1_C2,可以复用成以下功能之一:

  • spi0_clk
  • ts0_data4
  • uart4exp_ctsn

每个 GPIO 口的驱动电流、上下拉和重置后的初始状态都不尽相同,详细情况请参考《RK3288 规格书》中的 “RK3288 function IO description” 一章。

AIO-3288C 的 GPIO 驱动是在以下 pinctrl 文件中实现的:

kernel/drivers/pinctrl/pinctrl-rockchip.c

其核心是填充 GPIO bank 的方法和参数,并调用 gpiochip_add 注册到内核中。

使用

开发板有两个电源 LED 灯是 GPIO 口控制的,分别是:

_images/gpio1.png _images/gpio2.png

输入输出

下面以电源 LED 灯的驱动为例,讲述如何在内核编写代码控制 GPIO 口的输出。

首先需要在 firefly-rk3288-aio-3288c.dts 中增加驱动的资源描述:

firefly-led{
    compatible = "firefly,led";
    led-work = <&gpio8 GPIO_A6 GPIO_ACTIVE_HIGH>;
    led-power = <&gpio8 GPIO_A1 GPIO_ACTIVE_LOW>;
    status = "okay";
};

这里定义了两颗 LED 灯的 GPIO 设置:

led-power  GPIO8_A6  GPIO_ACTIVE_HIGH
led-user   GPIO8_A1  GPIO_ACTIVE_LOW

GPIO_ACTIVE_LOW 表示低电平有效,如果是高电平有效,需要替换为 GPIO_ACTIVE_HIGH 。 之后在驱动程序中加入对 GPIO 口的申请和控制则可:

#ifdef  CONFIG_OF
#include <linux/of.h>
#include <linux/of_gpio.h>
#endif 
static int firefly_led_probe(struct platform_device *pdev){
    int ret = -1;int gpio, flag;
    struct device_node *led_node = pdev->dev.of_node;   
    gpio = of_get_named_gpio_flags(led_node, "led-power", 0, &flag);
    if (!gpio_is_valid(gpio)){
        printk("invalid led-power: %d\n",gpio);
        return -1;
    } 
    if (gpio_request(gpio, "led_power")) {
        printk("gpio %d request failed!\n",gpio);
        return ret;
    }
    led_info.power_gpio = gpio;
    led_info.power_enable_value = (flag == OF_GPIO_ACTIVE_LOW) ? 0 : 1;
    gpio_direction_output(led_info.power_gpio, !(led_info.power_enable_value));
    ...
    on_error:gpio_free(gpio);
}

of_get_named_gpio_flags 从设备树中读取 led-power 的 GPIO 配置编号和标志,gpio_is_valid 判断该 GPIO 编号是否有效,gpio_request 则申请占用该 GPIO。如果初始化过程出错,需要调用 gpio_free 来释放之前申请过且成功的 GPIO 。

调用 gpio_direction_output 就可以设置输出高还是低电平,因为是 GPIO_ACTIVE_LOW ,如果要灯亮,需要写入 0 。

实际中如果要读出 GPIO,需要先设置成输入模式,然后再读取值:

int val;
gpio_direction_input(your_gpio);
val = gpio_get_value(your_gpio);

下面是常用的 GPIO API 定义:

#include <linux/gpio.h>
#include <linux/of_gpio.h> 
enum of_gpio_flags {
	OF_GPIO_ACTIVE_LOW = 0x1,
}; 
int of_get_named_gpio_flags(struct device_node *np, const char *propname,
			   int index, enum of_gpio_flags *flags); 
int gpio_is_valid(int gpio); 
int gpio_request(unsigned gpio, const char *label); 
void gpio_free(unsigned gpio); 
int gpio_direction_input(int gpio); 
int gpio_direction_output(int gpio, int v);

复用

如何定义 GPIO 有哪些功能可以复用,在运行时又如何切换功能呢?以 I2C4 为例作简单的介绍。查规格表可知,I2C4_SDA 与 I2C4_SCL 的功能定义如下:

Pad#	             func0	     func1
I2C4_SDA/GPIO7_C1	gpio7c1	     i2c4tp_sda
I2C4_SCL/GPIO7_C2	gpio7c2	     i2c4tp_scl

在 /kernel/arch/arm/boot/dts/rk3288.dtsi 里有:

i2c4: i2c@ff160000 {
    compatible = "rockchip,rk30-i2c";
    reg = <0xff160000 0x1000>;
    interrupts = <GIC_SPI 64 IRQ_TYPE_LEVEL_HIGH>;
    #address-cells = <1>;
    #size-cells = <0>;
    pinctrl-names = "default", "gpio";
    pinctrl-0 = <&i2c4_sda &i2c4_scl>;
    pinctrl-1 = <&i2c4_gpio>;
    gpios = <&gpio7 GPIO_C1 GPIO_ACTIVE_LOW>, <&gpio7 GPIO_C2 GPIO_ACTIVE_LOW>;
    clocks = <&clk_gates6 15>;
    rockchip,check-idle = <1>;
    status = "disabled";
};

此处,跟复用控制相关的是 pinctrl- 开头的属性:

  • pinctrl-names 定义了状态名称列表: default (i2c 功能) 和 gpio 两种状态。
  • pinctrl-0 定义了状态 0 (即 default)时需要设置的 pinctrl: i2c4_sda 和 i2c4_scl
  • pinctrl-1 定义了状态 1 (即 gpio)时需要设置的 pinctrl: i2c4_gpio

这些 pinctrl 在 /kernel/arch/arm/boot/dts/rk3288-pinctrl.dtsi 中定义:

/ { 
    pinctrl: pinctrl@ff770000 {
    compatible = "rockchip,rk3288-pinctrl";
    ...		
	gpio7_i2c4 {
        i2c4_sda:i2c4-sda {
            rockchip,pins = <I2C4TP_SDA>;
            rockchip,pull = <VALUE_PULL_DISABLE>;
            rockchip,drive = <VALUE_DRV_DEFAULT>;
            //rockchip,tristate = <VALUE_TRI_DEFAULT>;
        };
        i2c4_scl:i2c4-scl {
            rockchip,pins = <I2C4TP_SCL>;
            rockchip,pull = <VALUE_PULL_DISABLE>;
            rockchip,drive = <VALUE_DRV_DEFAULT>;
            //rockchip,tristate = <VALUE_TRI_DEFAULT>;
        };
        i2c4_gpio: i2c4-gpio {
            rockchip,pins = <FUNC_TO_GPIO(I2C4TP_SDA)>, <FUNC_TO_GPIO(I2C4TP_SCL)>;
            rockchip,drive = <VALUE_DRV_DEFAULT>;
        };
    };
    ...
}

I2C4TP_SDA, I2C4TP_SCL 的定义在 /kernel/arch/arm/boot/dts/include/dt-bindings/pinctrl/rockchip-rk3288.h 中:

#define GPIO7_C1 0x7c10
#define I2C4TP_SDA 0x7c11 
#define GPIO7_C2 0x7c20
#define I2C4TP_SCL 0x7c21

FUN_TO_GPIO 的定义在 /kernel/arch/arm/boot/dts/include/dt-bindings/pinctrl/rockchip.h 中:

#define FUNC_TO_GPIO(m)		((m) & 0xfff0)

也就是说 FUNC_TO_GPIO(I2C4TP_SDA) == GPIO7_C1, FUNC_TO_GPIO(I2C4TP_SCL) == GPIO7_C2 。 像 0x7c11 这样的值是有编码规则的:

0 c1 1
| |  `- func
| `---- offset
`------ bank

0x7c11 就表示 GPIO7_C1 func1, 即 I2C4TP_SDA 。

在复用时,如果选择了 “default” (即 i2c 功能),系统会应用 i2c1_sda 和 i2c1_scl 这两个 pinctrl,最终得将 GPIO0_A3 和 GPIO0_A2 两个针脚切换成对应的 i2c 功能;而如果选择了 “gpio” ,系统会应用 i2c1_gpio 这个 pinctrl,将 GPIO0_A3 和 GPIO0_A2 两个针脚还原为 GPIO 功能。我们看看 i2c 的驱动程序 /kernel/drivers/i2c/busses/i2c-rockchip.c 是如何切换复用功能的:

static int rockchip_i2c_probe(struct platform_device *pdev){
    struct rockchip_i2c *i2c = NULL;
    struct resource *res;
    struct device_node *np = pdev->dev.of_node;
    int ret;
    // ...
    i2c->sda_gpio = of_get_gpio(np, 0);
    if (!gpio_is_valid(i2c->sda_gpio)) {
        dev_err(&pdev->dev, "sda gpio is invalid\n");
        return -EINVAL;
    }
    ret = devm_gpio_request(&pdev->dev, i2c->sda_gpio, dev_name(&i2c->adap.dev));
    if (ret) {
        dev_err(&pdev->dev, "failed to request sda gpio\n");
        return ret;
    }
    i2c->scl_gpio = of_get_gpio(np, 1);
    if (!gpio_is_valid(i2c->scl_gpio)) {
        dev_err(&pdev->dev, "scl gpio is invalid\n");
        return -EINVAL;
    }
    ret = devm_gpio_request(&pdev->dev, i2c->scl_gpio, dev_name(&i2c->adap.dev));
    if (ret) {
        dev_err(&pdev->dev, "failed to request scl gpio\n");
        return ret;
    }
    i2c->gpio_state = pinctrl_lookup_state(i2c->dev->pins->p, "gpio");
    if (IS_ERR(i2c->gpio_state)) {
        dev_err(&pdev->dev, "no gpio pinctrl state\n");
        return PTR_ERR(i2c->gpio_state);
    }
    pinctrl_select_state(i2c->dev->pins->p, i2c->gpio_state);
    gpio_direction_input(i2c->sda_gpio);
    gpio_direction_input(i2c->scl_gpio);
    pinctrl_select_state(i2c->dev->pins->p, i2c->dev->pins->default_state);
    // ...
}

首先是调用 of_get_gpio 取出设备树中 i2c4 结点的 gpios 属于所定义的两个 gpio:

gpios = <&gpio7 GPIO_C1 GPIO_ACTIVE_LOW>, <&gpio7 GPIO_C2 GPIO_ACTIVE_LOW>;

然后是调用 devm_gpio_request 来申请 gpio,接着是调用 pinctrl_lookup_state 来查找 “gpio” 状态,而默认状态 “default” 已经由框架保存到 i2c->dev-pins->default_state 中了。最后调用 pinctrl_select_state 来选择是 “default” 还是 “gpio” 功能。 下面是常用的复用 API 定义:

#include <linux/pinctrl/consumer.h> 
struct device {
    //...
    #ifdef CONFIG_PINCTRL
    struct dev_pin_info	*pins;#endif//...}; 
    struct dev_pin_info {struct pinctrl *p;
    struct pinctrl_state *default_state;
    #ifdef CONFIG_PMstruct pinctrl_state *sleep_state;
    struct pinctrl_state *idle_state;#endif}; 
    struct pinctrl_state * pinctrl_lookup_state(struct pinctrl *p, const char *name); 
    int pinctrl_select_state(struct pinctrl *p, struct pinctrl_state *s);