linux 驱动之input子系统（gpio-keys）实现
１．概述
Gpio-keys 是基于input子系统实现的一个通用按键驱动，该驱动也符合linux驱动实现模型，即driver和device分离模型．一般按键驱动，都是基于gpio-keys进行开发的．
2. gpio-keys 代码分析（基于 linux 4.14.40）
（１）整体来说分为以下四步
static int gpio_keys_probe(struct platform_device *pdev)
{
...........
...........
/*第一，从设备树获取button,即gpio相关控制方式和属性*/
pdata = gpio_keys_get_devtree_pdata(dev);
...........
...........
/*第二，分配一个input 设备*/
input = devm_input_allocate_device(dev);
...........
...........
/*第三，注册gpio相关信息和分配资源*/
for (i = 0; i < pdata->nbuttons; i++) {
error = gpio_keys_setup_key(pdev, input, ddata,
button, i, child);
｝
...........
...........
/*第四，注册input 设备到kernel*/
error = input_register_device(input);
...........
...........
return 0;
}（２）从注册一个input设备来看，二,四步是一个通用的步骤，第三步和第一步是关键，先看第三步．
static int gpio_keys_setup_key(struct platform_device *pdev,
struct input_dev *input,
struct gpio_keys_drvdata *ddata,
const struct gpio_keys_button *button,
int idx,
struct fwnode_handle *child)
{
.............
.............
/*第一，请求gpio并获取irq 资源*/
error = devm_gpio_request_one(dev, button->gpio, flags, desc);
irq = gpiod_to_irq(bdata->gpiod);
.............
.............
/*第二，注册一个delayed work任务，这个任务的目的，当中断发生时，需要向
通过input子系统发消息，这个过程有可能会sleep或者schedule,所以必须通一个
delay work去完成这件事．
*/
INIT_DELAYED_WORK(&bdata->work, gpio_keys_gpio_work_func);
isr = gpio_keys_gpio_isr;
irqflags = IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING;}
.............
.............
/*第三，注册中断*/
error = devm_request_any_context_irq(dev, bdata->irq, isr, irqflags,
desc, bdata);
return 0;
}
（３）下面来看中断和delay work做了什么事
static irqreturn_t gpio_keys_gpio_isr(int irq, void *dev_id)
{
struct gpio_button_data *bdata = dev_id;
...............
...............
/*中断中，唯一做的事，就是把delay work加入到了system_wq队列中去．还做了一个延迟
这个延迟目的是为了去抖动．*/
mod_delayed_work(system_wq,
&bdata->work,
msecs_to_jiffies(bdata->software_debounce));
return IRQ_HANDLED;
}
static void gpio_keys_gpio_work_func(struct work_struct *work)
{
/*调用上报消息，接着向下看*/
...........
gpio_keys_gpio_report_event(bdata);
...........
}
static void gpio_keys_gpio_report_event(struct gpio_button_data *bdata)
{
............
/*第一步，获取gpio 状态．*/
state = gpiod_get_value_cansleep(bdata->gpiod);
............
/*发送消息到input*/
input_event(input, type, *bdata->code, state);
input_sync(input);
............
}（４）下面请看第一步工作，以及设备树的配置
（红色为必要部分）
- label : 一个key 的别名
- linux,code : 键值，作为按键的唯一识别号
- linux,input-type: input类型（EV_KEY(按键), EV_ABS（相对坐标）, EV_REL（绝对坐标）...) 默认为EV_KEY
- wakeup-source: 与pm相关，默认为disable
- linux,can-disable:是否共享中断line (（默认）0:shared, 1: not shared)
- debounce-interval : 去抖延时
- gpios : gpio 的相关信息
/*用于gpio资源的申请及初始化，可列举很多*/
gpio_keys_pins_default: gpio_keys_pins_default {
pinctrl-single,pins = <
AM4372_IOPAD(0x9a0, PIN_INPUT | MUX_MODE9) /* (L23) mcasp0_aclkr.gpio0[18] */
>;
};
/*创建gpio-keys 设备描述*/
gpio_keys: gpio_keys {
compatible = "gpio-keys";
pinctrl-names = "default";
pinctrl-0 = <&gpio_keys_pins_default>;
#address-cells = <1>;
#size-cells = <0>;
/*添加一个button, 用于做系统reset*/
button0 {
label = "reset";
linux,code = <0x198>; /*KEY_RESTART*/
gpios = <&gpio0 18 GPIO_ACTIVE_LOW>;
};
};3. 内核模块选择配置
| with configuration data saying which GPIOs are used. |
| |
| To compile this driver as a module, choose M here: the |
| module will be called gpio_keys. |
| |
| Symbol: KEYBOARD_GPIO [=y] |
| Type : tristate |
| Prompt: GPIO Buttons |
| Location: |
| -> Device Drivers |
| -> Input device support |
| -> Generic input layer (needed for keyboard, mouse, ...) (INPUT [=y]) |
| -> Keyboards (INPUT_KEYBOARD [=y]) |
| Defined at drivers/input/keyboard/Kconfig:214 |
| Depends on: !UML && INPUT [=y] && INPUT_KEYBOARD [=y] && (GPIOLIB [=y] || COMPILE_TEST [=n]) 4． cat /proc/bus/input/devices
通过这个可以看到接到input事件的handler是哪一个
$: cat /proc/bus/input/devices
I: Bus=0019 Vendor=0001 Product=0001 Version=0100
N: Name="gpio_keys"
P: Phys=gpio-keys/input0
S: Sysfs=/devices/platform/gpio_keys/input/input0
U: Uniq=
H: Handlers=event0
B: PROP=0
B: EV=3
B: KEY=1000000 0 0 0 0 0 0 0 0 0 0 0 0
/下面的信息有助于你编写udev rules
$:udevadm info -a -p /sys//devices/platform/gpio_keys/input/input0
looking at device '/devices/platform/gpio_keys/input/input0':
KERNEL=="input0"
SUBSYSTEM=="input"
DRIVER==""
ATTR{name}=="gpio_keys"
ATTR{phys}=="gpio-keys/input0"
ATTR{properties}=="0"
ATTR{uniq}==""
looking at parent device '/devices/platform/gpio_keys':
KERNELS=="gpio_keys"
SUBSYSTEMS=="platform"
DRIVERS=="gpio-keys"
ATTRS{disabled_keys}==""
ATTRS{disabled_switches}==""
ATTRS{driver_override}=="(null)"
ATTRS{keys}=="408"
ATTRS{switches}==""
looking at parent device '/devices/platform':
KERNELS=="platform"
SUBSYSTEMS==""
DRIVERS==""４．如何接收按键消息，以下例程供参考
#include
#include
#include
#include
#include
#include
#include
#include
#include
#define KEY_DEVICE_FILE "/dev/input/event0"
struct input_event {
struct timeval time;
unsigned short type;
unsigned short code;
int value;
};
int main()
{
int fd_key = -1;
struct input_event key_evt;
int ret = 0;
fd_key= open(KEY_DEVICE_FILE, O_RDONLY);
if(fd_key< 0) {
return fd_key;
}
monitor_key:
ret = read(fd_key, (char*)&key_evt, sizeof(struct input_event));
if(ret < 0)
{
printf("read key event failed:%d\n", ret);
}else{
if(key_evt.code == 408 && key_evt.value == 1)
{
printf("The press of reset button is detected\n");
return 0;
}
#if 0
printf("%lld seconds %ld microseconds", key_evt.time.tv_sec,
key_evt.time.tv_usec);
printf("type:%d code:%d value:%d\n", key_evt.type, key_evt.code, key_evt.value);
#endif
}
goto monitor_key;
return 0;
}