音频之手机物理按键（Exynos7872）

（注：本文仅仅用于个人理顺代码流程思路）
手机物理按键驱动文件分析：
一、GPIO的DTS文件，代码段如下所示：

/*gpio口的DTS定义*/
gpio_keys {status = "okay";compatible = "gpio-keys";#address-cells = <1>;#size-cells = <0>;pinctrl-names = "default";pinctrl-0 = <&key_home &key_voldown &key_volup &key_power>;button@1 {label = "gpio-keys: KEY_HOMEPAGE";interrupts = <4 0 0>;interrupt-parent = <&gpa1>;linux,code = <172>;gpios = <&gpa1 4 0xf>;gpio-key,wakeup = <1>;};button@2 {label = "gpio-keys: KEY_VOLUMEDOWN";interrupts = <6 0 0>;interrupt-parent = <&gpa1>;linux,code = <114>;gpios = <&gpa1 6 0xf>;};button@3 {label = "gpio-keys: KEY_VOLUMEUP";interrupts = <5 0 0>;interrupt-parent = <&gpa1>;linux,code = <115>;gpios = <&gpa1 5 0xf>;};button@4 {label = "gpio-keys: KEY_POWER";interrupts = <0 0 0>;interrupt-parent = <&gpa0>;linux,code = <116>;gpios = <&gpa0 0 0xf>;gpio-key,wakeup = <1>;};
};

二、驱动文件gpio_keys.c：
几个重要的结构体：

/*该结构体用来定义GPIO的按键功能*/
struct gpio_keys_platform_data {struct gpio_keys_button *buttons;       //指向gpio_keys_button结构体数组，用于按键的参数设置int nbuttons;                           //按键数组内元素个数unsigned int poll_interval;             //轮询时间间隔unsigned int rep:1;                     //自动重复使能输入子系统int (*enable)(struct device *dev);      void (*disable)(struct device *dev);    const char *name;                       //输入设备名
};/*用来关联input系统*/
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];
};/*** struct gpio_keys_button - configuration parameters* @code:       input event code (KEY_*, SW_*)* @gpio:       %-1 if this key does not support gpio* @active_low:     %true indicates that button is considered*          depressed when gpio is low* @desc:       label that will be attached to button's gpio* @type:       input event type (%EV_KEY, %EV_SW, %EV_ABS)* @wakeup:     configure the button as a wake-up source* @debounce_interval:  debounce ticks interval in msecs* @can_disable:    %true indicates that userspace is allowed to*          disable button via sysfs* @value:      axis value for %EV_ABS* @irq:        Irq number in case of interrupt keys* @gpiod:      GPIO descriptor*/
/*按键参数设置*/
struct gpio_keys_button {unsigned int code;int gpio;int active_low;const char *desc;unsigned int type;int wakeup;int debounce_interval;bool can_disable;int value;unsigned int irq;struct gpio_desc *gpiod;
};

1、平台驱动注册：

static int __init gpio_keys_init(void)
{return platform_driver_register(&gpio_keys_device_driver);
}

平台驱动结构体gpio_keys_device_driver定义：

static struct platform_driver gpio_keys_device_driver = {.probe      = gpio_keys_probe,.remove     = gpio_keys_remove,.driver     = {.name   = "gpio-keys",.pm = &gpio_keys_pm_ops,.of_match_table = of_match_ptr(gpio_keys_of_match),}
};static const struct of_device_id gpio_keys_of_match[] = {{ .compatible = "gpio-keys", },{ },
};

可以看到，平台驱动的name 是“gpio-keys”，linux统一设备模型的平台驱动与设备就是通过name进行匹配的，当驱动被注册进内核，该驱动就会去检索相同name的设备，找到后就会开始执行probe回调函数。很显然，该驱动文件对应的就是前面dts文件所定义的GPIO按键。

2、probe回调函数：

/*probe回调函数*/
gpio_keys_probe(struct platform_device *pdev)|-- gpio_keys_get_devtree_pdata(dev);   //从设备树中获取GPIO数据|-- devm_input_allocate_device(dev);    //分配input设备|-- gpio_keys_open|-- gpio_keys_report_state(ddata);|-- gpio_keys_gpio_report_event(bdata);|-- gpio_get_value_cansleep(button->gpio);//读键值|-- exynos_ss_check_crash_key(button->code, state);|-- input_event(input, type, button->code, button->value);//上报event|-- gpio_keys_close|-- gpio_keys_setup_key(pdev, input, bdata, button)//设置GPIO_key|-- INIT_DELAYED_WORK(&bdata->work, gpio_keys_gpio_work_func)//工作队列|-- gpio_keys_gpio_work_func|-- gpio_keys_gpio_report_event(bdata);//event上报函数|-- gpio_get_value_cansleep(button->gpio);//读键值|-- exynos_ss_check_crash_key(button->code, state);|-- input_event(input, type, button->code, button->value);//上报event事件|-- sysfs_create_group(&pdev->dev.kobj, &gpio_keys_attr_group);//在sys目录下创建属性文件|-- input_register_device(input);//input设备注册|-- device_init_wakeup(&pdev->dev, wakeup);//设备唤醒初始化|-- device_set_wakeup_capable(dev, val);//设备能不能被唤醒|-- device_set_wakeup_enable(dev, val);//设备使不使用唤醒

以上是probe回调函数的整个执行过程，下面来具体的分析一下上述的部分函数：
gpio_keys_setup_key(pdev, input, bdata, button)；

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)
{const char *desc = button->desc ? button->desc : "gpio_keys";/*@desc:label that will be attached to button's gpio*/struct device *dev = &pdev->dev;irq_handler_t isr;unsigned long irqflags;int irq;int error;bdata->input = input;bdata->button = button;spin_lock_init(&bdata->lock);if (gpio_is_valid(button->gpio)) {error = devm_gpio_request_one(&pdev->dev, button->gpio,GPIOF_IN, desc);if (error < 0) {dev_err(dev, "Failed to request GPIO %d, error %d\n",button->gpio, error);return error;}if (button->debounce_interval) {error = gpio_set_debounce(button->gpio,button->debounce_interval * 1000);/* use timer if gpiolib doesn't provide debounce */if (error < 0)bdata->software_debounce =button->debounce_interval;}if (button->irq) {bdata->irq = button->irq;} else {irq = gpio_to_irq(button->gpio);if (irq < 0) {error = irq;dev_err(dev,"Unable to get irq number for GPIO %d, error %d\n",button->gpio, error);return error;}bdata->irq = irq;}INIT_DELAYED_WORK(&bdata->work, gpio_keys_gpio_work_func);/*工作队列初始化，定义一个gpio_keys_gpio_work_func工作队列函数去检测按键状态*/isr = gpio_keys_gpio_isr;irqflags = IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING;} else {if (!button->irq) {dev_err(dev, "No IRQ specified\n");return -EINVAL;}bdata->irq = button->irq;if (button->type && button->type != EV_KEY) {dev_err(dev, "Only EV_KEY allowed for IRQ buttons.\n");return -EINVAL;}bdata->release_delay = button->debounce_interval;setup_timer(&bdata->release_timer,gpio_keys_irq_timer, (unsigned long)bdata);isr = gpio_keys_irq_isr;irqflags = 0;}input_set_capability(input, button->type ?: EV_KEY, button->code);/** Install custom action to cancel release timer and* workqueue item.*/error = devm_add_action(&pdev->dev, gpio_keys_quiesce_key, bdata);if (error) {dev_err(&pdev->dev,"failed to register quiesce action, error: %d\n",error);return error;}/** If platform has specified that the button can be disabled,* we don't want it to share the interrupt line.*/if (!button->can_disable)irqflags |= IRQF_SHARED;if (button->wakeup)irqflags |= IRQF_NO_SUSPEND;error = devm_request_any_context_irq(&pdev->dev, bdata->irq,isr, irqflags, desc, bdata);if (error < 0) {dev_err(dev, "Unable to claim irq %d; error %d\n",bdata->irq, error);return error;}return 0;
}

gpio_keys_gpio_work_func函数定义：

static void gpio_keys_gpio_work_func(struct work_struct *work)
{struct gpio_button_data *bdata =container_of(work, struct gpio_button_data, work.work);gpio_keys_gpio_report_event(bdata);if (bdata->button->wakeup)pm_relax(bdata->input->dev.parent);
}

gpio_keys_gpio_report_event(bdata)函数定义：

static void gpio_keys_gpio_report_event(struct gpio_button_data *bdata)
{const struct gpio_keys_button *button = bdata->button;struct input_dev *input = bdata->input;unsigned int type = button->type ?: EV_KEY;int state = gpio_get_value_cansleep(button->gpio);/*获取物理按键的状态值*/struct irq_desc *desc = irq_to_desc(gpio_to_irq(button->gpio));if (!desc) {dev_err(input->dev.parent, "irq_desc is null! (gpio=%d)\n",button->gpio);return;}if (state < 0) {dev_err(input->dev.parent, "failed to get gpio state\n");return;}state = (state ? 1 : 0) ^ button->active_low;exynos_ss_check_crash_key(button->code, state);/*该函数是烧录版本的时候按键的操作函数*/if (type == EV_ABS) {if (state)input_event(input, type, button->code, button->value);//上报event事件} else {input_event(input, type, button->code,irqd_is_wakeup_set(&desc->irq_data) ? 1 : !!state);}input_sync(input);
}

exynos_ss_check_crash_key(button->code, state)定义如下：

#ifdef CONFIG_EXYNOS_SNAPSHOT_CRASH_KEY
void exynos_ss_check_crash_key(unsigned int code, int value)
{static bool volup_p;static bool voldown_p;static int loopcount;static const unsigned int VOLUME_UP = KEY_VOLUMEUP;static const unsigned int VOLUME_DOWN = KEY_VOLUMEDOWN;/* Enter Forced Upload 进入版本下载操作如下：*  Hold volume down key first*  and then press power key twice*  and volume up key should not be pressed*/if (value) {if (code == VOLUME_UP)volup_p = true;if (code == VOLUME_DOWN)voldown_p = true;if (!volup_p && voldown_p) {if (code == KEY_POWER) {pr_info("exynos-snapshot: count for entering forced upload [%d]\n",++loopcount);if (loopcount == 2) {panic("Crash Key");}}}} else {if (code == VOLUME_UP)volup_p = false;if (code == VOLUME_DOWN) {loopcount = 0;voldown_p = false;}}
}
#endif

三、手机的物理按键从原理图中可知，是直接接在CPU上的，底层驱动通过一个输入设备进行按键的检测，底层有个映射表（【samsung7872】【Z205】文件名：input-event-codes.h），为每个按键都分配了键值，当input设备检测到了按键按下，就会去该按键在映射表中相对应的键值，然后input子系统将获取到的键值上报给上层进行相应的处理。

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音频之手机物理按键（Exynos7872）

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