GPIO子系统¶
对于像 LED 这样直接连接到 GPIO 控制器的设备，可以直接使用 GPIO 子系统的方式来描述设备所使用的 GPIO 资源。
设备树描述¶
对于 GPIO 控制器，对应的设备节点需要声明 gpio-controller 属性，并设置 #gpio-cells 的大小，比如 rk3399 的 GPIO 控制器而言，由原厂 BSP 工程师编写代码如下：
rk3399.dtsi
gpio0: gpio0@ff720000 {
compatible = "rockchip,gpio-bank";
reg = <0x0 0xff720000 0x0 0x100>;
clocks = <&pmucru PCLK_GPIO0_PMU>;
interrupts = <GIC_SPI 14 IRQ_TYPE_LEVEL_HIGH 0>;
gpio-controller;
#gpio-cells = <0x2>;
interrupt-controller;
#interrupt-cells = <0x2>;
};
gpio1: gpio1@ff730000 {
compatible = "rockchip,gpio-bank";
reg = <0x0 0xff730000 0x0 0x100>;
clocks = <&pmucru PCLK_GPIO1_PMU>;
interrupts = <GIC_SPI 15 IRQ_TYPE_LEVEL_HIGH 0>;
gpio-controller;
#gpio-cells = <0x2>;
interrupt-controller;
#interrupt-cells = <0x2>;
};
驱动开发人员如果需要让某个设备引用 GPIO 资源，则可以在设备树中直接添加描述。注意，这种方式只能在 BSP 原厂工程师已经添加了 GPIO 控制器的描述时使用：
rk3399-firefly.dts
leds {
compatible = "gpio-leds";
pinctrl-names = "default";
pinctrl-0 = <&work_led_pin>, <&diy_led_pin>;
work_led: led-0 {
label = "work";
default-state = "on";
gpios = <&gpio2 RK_PD3 GPIO_ACTIVE_HIGH>;
};
diy_led: led-1 {
label = "diy";
default-state = "off";
gpios = <&gpio0 RK_PB5 GPIO_ACTIVE_HIGH>;
};
};
GPIO 还可以有其他属性，比如：
- ngpios=<18>：表示该 GPIO 控制器有 18 个引脚
- gpio-ranges=<&pinctrl1 0 20 10>：表示该 GPIO 的 0 ~ 9 引脚映射到 pinctrl1 的 20 ~ 29 引脚
数据结构¶
struct gpio_device {
int id;
struct device dev;
struct cdev chrdev;
struct device *mockdev;
struct module *owner;
struct gpio_chip *chip;
struct gpio_desc *descs;
int base;
u16 ngpio;
const char *label;
void *data;
struct list_head list;
struct blocking_notifier_head notifier;
struct rw_semaphore sem;
#ifdef CONFIG_PINCTRL
/*
* If CONFIG_PINCTRL is enabled, then gpio controllers can optionally
* describe the actual pin range which they serve in an SoC. This
* information would be used by pinctrl subsystem to configure
* corresponding pins for gpio usage.
*/
struct list_head pin_ranges;
#endif
};
每个 GPIO controller 都会用一个struct gpio_device结构体来表示，其中：
-
在
struct gpio_chip中提供引脚操作函数 -
在
struct gpio_desc中提供每个引脚的信息
struct gpio_chip {
const char *label;
struct gpio_device *gpiodev;
struct device *parent;
struct module *owner;
int (*request)(struct gpio_chip *gc,
unsigned int offset);
void (*free)(struct gpio_chip *gc,
unsigned int offset);
int (*get_direction)(struct gpio_chip *gc,
unsigned int offset);
int (*direction_input)(struct gpio_chip *gc,
unsigned int offset);
int (*direction_output)(struct gpio_chip *gc,
unsigned int offset, int value);
int (*get)(struct gpio_chip *gc,
unsigned int offset);
int (*get_multiple)(struct gpio_chip *gc,
unsigned long *mask,
unsigned long *bits);
void (*set)(struct gpio_chip *gc,
unsigned int offset, int value);
void (*set_multiple)(struct gpio_chip *gc,
unsigned long *mask,
unsigned long *bits);
int (*set_config)(struct gpio_chip *gc,
unsigned int offset,
unsigned long config);
int (*to_irq)(struct gpio_chip *gc,
unsigned int offset);
void (*dbg_show)(struct seq_file *s,
struct gpio_chip *gc);
int (*init_valid_mask)(struct gpio_chip *gc,
unsigned long *valid_mask,
unsigned int ngpios);
int (*add_pin_ranges)(struct gpio_chip *gc);
int base;
u16 ngpio;
u16 offset;
const char *const *names;
bool can_sleep;
};
label：GPIO控制器名称
gpiodevice：GPIO控制器设备
parent：GPIO控制器父设备
base：GPIO引脚基值
ngpio：GPIO引脚数量
offset：GPIO引脚偏移
names：GPIO引脚名称
can_sleep：是否可以在睡眠状态下访问GPIO
使用gpiochip_add_data()宏来注册struct gpio_chip。
GPIO 中的每个引脚都对应一个struct gpio_desc，引脚信息被保存在一个链表中：
struct gpio_desc {
struct gpio_device *gdev;
unsigned long flags;
/* flag symbols are bit numbers */
#define FLAG_REQUESTED 0
#define FLAG_IS_OUT 1
#define FLAG_EXPORT 2 /* protected by sysfs_lock */
#define FLAG_SYSFS 3 /* exported via /sys/class/gpio/control */
#define FLAG_ACTIVE_LOW 6 /* value has active low */
#define FLAG_OPEN_DRAIN 7 /* Gpio is open drain type */
#define FLAG_OPEN_SOURCE 8 /* Gpio is open source type */
#define FLAG_USED_AS_IRQ 9 /* GPIO is connected to an IRQ */
#define FLAG_IRQ_IS_ENABLED 10 /* GPIO is connected to an enabled IRQ */
#define FLAG_IS_HOGGED 11 /* GPIO is hogged */
#define FLAG_TRANSITORY 12 /* GPIO may lose value in sleep or reset */
#define FLAG_PULL_UP 13 /* GPIO has pull up enabled */
#define FLAG_PULL_DOWN 14 /* GPIO has pull down enabled */
#define FLAG_BIAS_DISABLE 15 /* GPIO has pull disabled */
#define FLAG_EDGE_RISING 16 /* GPIO CDEV detects rising edge events */
#define FLAG_EDGE_FALLING 17 /* GPIO CDEV detects falling edge events */
#define FLAG_EVENT_CLOCK_REALTIME 18 /* GPIO CDEV reports REALTIME timestamps in events */
/* Connection label */
const char *label;
/* Name of the GPIO */
const char *name;
#ifdef CONFIG_OF_DYNAMIC
struct device_node *hog;
#endif
#ifdef CONFIG_GPIO_CDEV
/* debounce period in microseconds */
unsigned int debounce_period_us;
#endif
};
gdev：属于哪个GPIO controller
flags：标志位，表示引脚的状态
label：一般等于
struct gpio_chip的labelname：引脚名
GPIO函数接口¶
GPIO 的函数接口有两套：legacy 模式和基于 descriptor 的。由于第一套已被废弃，这里只介绍基于 descriptor 的。
获取GPIO描述符¶
struct gpio_desc *gpiod_get(struct device *dev,
const char *con_id,
enum gpiod_flags flags);
struct gpio_desc *gpiod_get_index(struct device *dev,
const char *con_id,
unsigned int idx,
enum gpiod_flags flags);
struct gpio_descs *gpiod_get_array(struct device *dev,
const char *con_id,
enum gpiod_flags flags);
struct gpio_desc *devm_gpiod_get(struct device *dev,
const char *con_id,
enum gpiod_flags flags);
struct gpio_desc *devm_gpiod_get_index(struct device *dev,
const char *con_id,
unsigned int idx,
enum gpiod_flags flags);
struct gpio_descs *devm_gpiod_get_array(struct device *dev,
const char *con_id,
enum gpiod_flags flags);
其中 gpiod_flags 如下：
enum gpiod_flags {
GPIOD_ASIS = 0,
GPIOD_IN = GPIOD_FLAGS_BIT_DIR_SET,
GPIOD_OUT_LOW = GPIOD_FLAGS_BIT_DIR_SET | GPIOD_FLAGS_BIT_DIR_OUT,
GPIOD_OUT_HIGH = GPIOD_FLAGS_BIT_DIR_SET | GPIOD_FLAGS_BIT_DIR_OUT |
GPIOD_FLAGS_BIT_DIR_VAL,
GPIOD_OUT_LOW_OPEN_DRAIN = GPIOD_OUT_LOW | GPIOD_FLAGS_BIT_OPEN_DRAIN,
GPIOD_OUT_HIGH_OPEN_DRAIN = GPIOD_OUT_HIGH | GPIOD_FLAGS_BIT_OPEN_DRAIN,
};
重要标志位
- GPIOD_ASIS：不初始化GPIO
- GPIOD_IN：将GPIO初始化为输入端
- GPIOD_OUT_LOW：将GPIO初始化为输出端，并将值设置为0
- GPIOD_OUT_HIGH：将GPIO初始化为输出端，并将值设置为1
假如有设备树描述如下所示：
foo_device {
compatible = "acme, foo";
...
led-gpios <&gpioa 15 GPIO_ACTIVE_HIGH>, /*red*/
<&gpiob 16 GPIO_ACTIVE_HIGH>, /*green*/
<&gpioc 17 GPIO_ACTIVE_HIGH>; /*blue*/
power-gpios = <&gpiob 1 GPIO_ACTIVE_LOW>;
};
这里 led-gpios 中的 led 就是 function，&gpioa 是特定 GPIO 控制器节点的 pointer handle，数字 15、16、17 是每个 GPIO 控制器的编号，GPIO_ACTIVE_HIGH 就是标志位。在驱动程序中获取 GPIO 资源可以这么做：
struct gpio_desc *gpio_red = gpiod_get_index(dev, "led", 0, GPIO_ACTIVE_HIGH);
struct gpio_desc *gpio_green = gpiod_get_index(dev, "led", 1, GPIO_ACTIVE_HIGH);
struct gpio_desc *gpio_blue = gpiod_get_index(dev, "led", 2, GPIO_ACTIVE_HIGH);
struct gpio_desc *gpio_power = gpiod_get(dev, "power", GPIO_ACTIVE_LOW);
设置GPIO方向¶
编写需要控制 GPIO 的驱动程序时，必须指定方向。可以直接使用带 flags 参数的devm_gpio_get()函数，或者如果 flags 设置为 GPIOD_ASIS 时，就可以在随后调用gpiod_direction_input()或gpiod_direction_output()来设置方向：
int gpiod_direction_input(struct gpio_desc *desc);
int gpiod_direction_output(struct gpio_desc *desc, int value);
获取GPIO电平¶
int gpiod_get_value(const struct gpio_desc *desc);
void gpiod_set_value(struct gpio_desc *desc, int value);
Linux 驱动程序不关注物理电路的实现，所有的gpoid_set_value_xxx()函数均使用逻辑值进行操作——将参数 value 解释为“有效”（“1”）或者“无效”（“0”），函数会自动地设置响应的物理电路。
在 GPIO 的世界中，有两种常见的逻辑电平：
- 高电平有效（High Active）：在这个模式下，逻辑高（通常是1或3V以上）表示引脚的激活状态。
- 低电平有效（Low Active）：在这个模式下，逻辑低（通常是0V或GND）表示引脚的激活状态。
如果一条物理线路被设置为低电平有效，当调用gpio_set_value(gpio, 1)时，会自动设置物理电路为低电平。
相关函数汇总
| 函数名 | 电平有效属性 | 物理线路 |
|---|---|---|
| gpiod_set_value(gpio, 0) | 高电平有效 | 配置为低电平 |
| gpiod_set_value(gpio, 1) | 高电平有效 | 配置为高电平 |
| gpiod_set_value(gpio, 0) | 低电平有效 | 配置为高电平 |
| gpiod_set_value(gpio, 1) | 低电平有效 | 配置为低电平 |
获取GPIO中断号¶
中断请求可以通过 GPIO 触发，使用以下函数获取与给定 GPIO 对应的 irq 号：
该函数通过传递一个 GPIO descriptor，返回 irq 号，如果该 GPIO 没有与中断控制器连接，则返回 -EINVAL。
该函数返回的 irq 号可以用在request_irq()和free_irq()函数中。
释放GPIO：
与Pinctrl子系统交互¶
- 在 GPIO 设备树中使用
gpio-ranges来描述它们之间的联系 - 解析这些联系，在注册
struct gpio-chip时自动调用 - 在 GPIO 驱动程序中，提供
gpio_chip->request函数；在 Pinctrl 子系统中，提供pmxops->gpio_request_enable()函数或者pmxops->request()函数
简单示例¶
#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/platform_device.h> /* For platform devices */
#include <linux/gpio/consumer.h> /* For GPIO Descriptor interface */
#include <linux/interrupt.h> /* For IRQ */
#include <linux/of.h> /* For DT*/
/*
* Let us consider the bellow mapping
*
* foo_device {
* compatible = "packt,gpio-descriptor-sample";
* led-gpios = <&gpio2 15 GPIO_ACTIVE_HIGH>, // red
* <&gpio2 16 GPIO_ACTIVE_HIGH>, // green
*
* btn1-gpios = <&gpio2 1 GPIO_ACTIVE_LOW>;
* btn2-gpios = <&gpio2 1 GPIO_ACTIVE_LOW>;
* };
*/
static struct gpio_desc *red, *green, *btn1, *btn2;
static int irq;
static irqreturn_t btn1_pushed_irq_handler(int irq, void *dev_id)
{
int state;
/* read the button value and change the led state */
state = gpiod_get_value(btn2);
gpiod_set_value(red, state);
gpiod_set_value(green, state);
pr_info("btn1 interrupt: Interrupt! btn2 state is %d)\n", state);
return IRQ_HANDLED;
}
static const struct of_device_id gpiod_dt_ids[] = {
{ .compatible = "packt,gpio-descriptor-sample", },
{ /* sentinel */ }
};
static int my_pdrv_probe (struct platform_device *pdev)
{
int retval;
struct device *dev = &pdev->dev;
/*
* We use gpiod_get/gpiod_get_index() along with the flags
* in order to configure the GPIO direction and an initial
* value in a single function call.
*
* One could have used:
* red = gpiod_get_index(dev, "led", 0);
* gpiod_direction_output(red, 0);
*/
red = gpiod_get_index(dev, "led", 0, GPIOD_OUT_LOW);
green = gpiod_get_index(dev, "led", 1, GPIOD_OUT_LOW);
/*
* Configure Button GPIOs as input
*
* After this, one can call gpiod_set_debounce()
* only if the controller has the feature
* For example, to debounce a button with a delay of 200ms
* gpiod_set_debounce(btn1, 200);
*/
btn1 = gpiod_get(dev, "btn1", GPIOD_IN);
btn2 = gpiod_get(dev, "btn2", GPIOD_IN);
irq = gpiod_to_irq(btn1);
retval = request_threaded_irq(irq, NULL,
btn1_pushed_irq_handler,
IRQF_TRIGGER_LOW | IRQF_ONESHOT,
"gpio-descriptor-sample", NULL);
pr_info("Hello! device probed!\n");
return 0;
}
static int my_pdrv_remove(struct platform_device *pdev)
{
free_irq(irq, NULL);
gpiod_put(red);
gpiod_put(green);
gpiod_put(btn1);
gpiod_put(btn2);
pr_info("good bye reader!\n");
return 0;
}
static struct platform_driver mypdrv = {
.probe = my_pdrv_probe,
.remove = my_pdrv_remove,
.driver = {
.name = "gpio_descriptor_sample",
.of_match_table = of_match_ptr(gpiod_dt_ids),
.owner = THIS_MODULE,
},
};
module_platform_driver(mypdrv);
MODULE_AUTHOR("John Madieu <john.madieu@gmail.com>");
MODULE_LICENSE("GPL");