深入解析Linux GPIO-key驱动机制
最编程
2024-02-19 08:57:44
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测试平台
本文介绍的代码在以下平台进行测试：
- Host：Ubuntu14.04
- Target：Firefly-rk3288
- Compiler:arm-linux-android-gcc
架构
gpio-keys驱动基于Linux内核的input子系统实现，设备驱动以platform_device的方式注册到系统中。驱动对于按键基于中断的处理方式实现，并且通过input子系统将按键事件上报到应用层，供应用程序解析使用。
DTS配置
位于 Documentation/devicetree/bindings/gpio/gpio-keys.txt介绍了对于gpio-keys驱动程序的Device-Tree bingdings。其支持的属性定义如下，关于DTS基本语法的总结可以参见。
Required properties
- - compatible = "gpio-keys";
该属性定义了设备的兼容性。
Optional properties
- -autorepeat: Boolean,启动input子系统的auto repeat特性。
Subnode properties
每一个button(key)都对应为gpio-keys的一个子节点，子节点的属性包括：
- - gpios: device-tree gpio规格属性。
- - label: key的描述性名称。
- - linux,code: input子系统所定义的按键代码，参见：include/dt-bindings/input/input.h关于keys和buttons的code定义。
Optional subnode-properties
- -linux,input-type:定义该key/button所依赖的event type(input子系统定义)，默认为1 == EV_KEY。
- -debounce-interval:定义该key/button的去抖间隔，默认为5ms。
- -gpio-key,wakeup:Boolean，标识该key可以唤醒系统，例如，Android系统的power-key。
Example nodes:
gpio_keys_test { compatible = "gpio-keys"; #address-cells = <1>; #size-cells = <0>; autorepeat; powerkey { label = "power key"; linux,code = <116>; gpios = <&gpio0 GPIO_A5 GPIO_ACTIVE_LOW>; gpio-key,wakeup; debounce-interval = <5>; }; };
基本数据结构
/* key/button的基本配置参数 */ struct gpio_keys_button { unsigned int code; /* input event code (KEY_*, SW_*) */ int gpio; /* -1 if this key does not support gpio */ int active_low; const char *desc; unsigned int type; /* input event type (EV_KEY, EV_SW, EV_ABS) */ int wakeup; /* configure the button as a wake-up source */ int debounce_interval; /* debounce ticks interval in msecs */ bool can_disable; int value; /* axis value for EV_ABS */ unsigned int irq; /* Irq number in case of interrupt keys */ }; /*key/button控制逻辑配置参数*/ struct gpio_button_data { const struct gpio_keys_button *button; struct input_dev *input; struct timer_list timer; struct work_struct work; unsigned int timer_debounce; /* in msecs */ unsigned int irq; spinlock_t lock; bool disabled; bool key_pressed; }; /*key/button platform配置参数*/ struct gpio_keys_platform_data { struct gpio_keys_button *buttons; int nbuttons; unsigned int poll_interval; /* polling interval in msecs - for polling driver only */ unsigned int rep:1; /* enable input subsystem auto repeat */ int (*enable)(struct device *dev); void (*disable)(struct device *dev); const char *name; /* input device name */ }; /*key/button plaform_device data配置参数，该结构作为platform data注册到platform设备总线*/ struct gpio_keys_drvdata { const struct gpio_keys_platform_data *pdata; struct input_dev *input; struct mutex disable_lock; struct gpio_button_data data[0]; };
设备注册
gpio-keys驱动是以platform_driver的身份注册到系统中的，所以其需要定义platfrom_driver结构，如下：
static struct platform_driver gpio_keys_device_driver = { .probe = gpio_keys_probe,//gpio-keys驱动初始化函数 .remove = gpio_keys_remove,//gpio-keys驱动卸载处理函数 .driver = { .name = "gpio-keys", .owner = THIS_MODULE, .pm = &gpio_keys_pm_ops, .of_match_table = of_match_ptr(gpio_keys_of_match),//定义驱动的兼容属性，具体定义如下： } }; static struct of_device_id gpio_keys_of_match[] = { { .compatible = "gpio-keys", }, { }, };
设备probe流程
下面主要分析一下驱动的probe主要流程，较为细节的代码请参照内核代码。
static int gpio_keys_probe(struct platform_device *pdev) { ... ... if (!pdata) { pdata = gpio_keys_get_devtree_pdata(dev);------------------------------------------->(1) if (IS_ERR(pdata)) return PTR_ERR(pdata); } ddata = kzalloc(sizeof(struct gpio_keys_drvdata) + pdata->nbuttons * sizeof(struct gpio_button_data), GFP_KERNEL); input = input_allocate_device();--------------------------------------------------------(2) if (!ddata || !input) { dev_err(dev, "failed to allocate state\n"); error = -ENOMEM; goto fail1; } platform_set_drvdata(pdev, ddata); input_set_drvdata(input, ddata); input->name = pdata->name ? : pdev->name; input->phys = "gpio-keys/input0"; input->dev.parent = &pdev->dev; input->open = gpio_keys_open; input->close = gpio_keys_close; ... ... /* Enable auto repeat feature of Linux input subsystem */ if (pdata->rep) __set_bit(EV_REP, input->evbit); for (i = 0; i < pdata->nbuttons; i++) {--------------------------------------------（3） const struct gpio_keys_button *button = &pdata->buttons[i]; struct gpio_button_data *bdata = &ddata->data[i]; error = gpio_keys_setup_key(pdev, input, bdata, button); if (error) goto fail2; if (button->wakeup) wakeup = 1; } error = sysfs_create_group(&pdev->dev.kobj, &gpio_keys_attr_group);----------------(4) if (error) { dev_err(dev, "Unable to export keys/switches, error: %d\n", error); goto fail2; } error = input_register_device(input);---------------------------------------------（5） if (error) { dev_err(dev, "Unable to register input device, error: %d\n", error); goto fail3; } device_init_wakeup(&pdev->dev, wakeup); return 0; ... ... }
- (1)解析DTS关于gpio-keys的属性定义，创建、初始化gpio_keys_platform_data。
- (2)分配、初始化input设备。
- (3)遍历所有key/button,注册key/buton所需的资源(gpio、irq等)。
- (4)注册gpio-keys在sys文件系统下的访问接口属性，gpio-keys设备在sys文件系统路径为：/sys/devices/gpio_keys_test.32，其中gpio_keys_test为DTS中设备设备节点名称。
- (5)注册input设备。
设备资源解析
gpio_keys_get_devtree_pdata函数完成将DTS节点的设备属性翻译成gpio_keys_platform_data结构，具体执行流程如下。
gpio_keys_get_devtree_pdata(struct device *dev) { ... ... nbuttons = of_get_child_count(node);-----------------------------------------------(1) if (nbuttons == 0) { error = -ENODEV; goto err_out; } pdata = kzalloc(sizeof(*pdata) + nbuttons * (sizeof *button), GFP_KERNEL); if (!pdata) { error = -ENOMEM; goto err_out; } pdata->buttons = (struct gpio_keys_button *)(pdata + 1); pdata->nbuttons = nbuttons; pdata->rep = !!of_get_property(node, "autorepeat", NULL); i = 0; for_each_child_of_node(node, pp) {------------------------------------------------(2) int gpio; enum of_gpio_flags flags; if (!of_find_property(pp, "gpios", NULL)) { pdata->nbuttons--; dev_warn(dev, "Found button without gpios\n"); continue; } gpio = of_get_gpio_flags(pp, 0, &flags); if (gpio < 0) { error = gpio; if (error != -EPROBE_DEFER) dev_err(dev, "Failed to get gpio flags, error: %d\n", error); goto err_free_pdata; } button = &pdata->buttons[i++]; button->gpio = gpio; button->active_low = flags & OF_GPIO_ACTIVE_LOW; if (of_property_read_u32(pp, "linux,code", &button->code)) { dev_err(dev, "Button without keycode: 0x%x\n", button->gpio); error = -EINVAL; goto err_free_pdata; } button->desc = of_get_property(pp, "label", NULL); if (of_property_read_u32(pp, "linux,input-type", &button->type)) button->type = EV_KEY; button->wakeup = !!of_get_property(pp, "gpio-key,wakeup", NULL); if (of_property_read_u32(pp, "debounce-interval", &button->debounce_interval)) button->debounce_interval = 5; } if (pdata->nbuttons == 0) { error = -EINVAL; goto err_free_pdata; } return pdata; }
- (1)获取keys/button的节点数量，初始化input系统的autorepeat属性。
- (2)遍历DTS所有子节点，依次读取key/button的gpios、flags、linux，code、linux,input-type、gpio-key,wakeup、debounce-interval属性字段。
按键注册
gpio_keys_setup_key主要完成gpio的申请、配置以及gpio所关联的irq的申请、初始化配置功能，具体执行流程如下。
static int gpio_keys_setup_key(struct platform_device *pdev, struct input_dev *input, struct gpio_button_data *bdata, const struct gpio_keys_button *button) { ...... if (gpio_is_valid(button->gpio)) { error = gpio_request_one(button->gpio, GPIOF_IN, desc);----------------------------->(1) if (error < 0) { dev_err(dev, "Failed to request GPIO %d, error %d\n", button->gpio, error); return error; } if (button->debounce_interval) {---------------------------------------------------->(2) error = gpio_set_debounce(button->gpio, button->debounce_interval * 1000); /* use timer if gpiolib doesn't provide debounce */ if (error < 0) bdata->timer_debounce = button->debounce_interval; } irq = gpio_to_irq(button->gpio);--------------------------------------------------->(3) if (irq < 0) { error = irq; dev_err(dev, "Unable to get irq number for GPIO %d, error %d\n",上一篇： SS和Netstat查询得到的结果有差异