【TINY4412】LINUX移植笔记：（7）LED驱动分析
【TINY4412】LINUX移植笔记：（7）LED驱动分析
宿主机 ： 虚拟机 Ubuntu 16.04 LTS / X64
目标板[底板]： Tiny4412SDK - 1506
目标板[核心板]： Tiny4412 - 1412
LINUX内核： 4.12.0
交叉编译器： gcc-arm-none-eabi-5_4-2016q3
日期： 2017-7-22 12:08:02
作者： SY
简介
Tiny4412开发板上有4个LED自定义指示灯，我们使用LED1作为Heartbeat心跳。只要系统正常运行，小灯便永不停息，就像人的心跳一样！
对于LINUX来说，最好的方式是：只需一种驱动便可适配多个设备，驱动可以自由的管理设备的安装、卸载、打开、关闭等操作。
设备树本质上和xml文件类似，主要用来被内核做字符串解析，是一个静态文本。就像安卓的页面配置文件activity_main.xml用来描述页面的布局，元素等。
分析设备
在LINUX 3.5以后，都是使用内核设备树配置外设。也就是说，很多驱动在LINUX内核源码层次，不用修改，只要配置dts，然后在menuconfig中打开就行了。
root@ubuntu:/opt/linux-4.12# more arch/arm/boot/dts/exynos4412-tiny4412.dts
leds {
compatible = "gpio-leds";
led1 {
label = "led1";
gpios = <&gpm4 0 GPIO_ACTIVE_LOW>;
default-state = "off";
linux,default-trigger = "heartbeat";
};
led2 {
label = "led2";
gpios = <&gpm4 1 GPIO_ACTIVE_LOW>;
default-state = "off";
};
led3 {
label = "led3";
gpios = <&gpm4 2 GPIO_ACTIVE_LOW>;
default-state = "off";
};
led4 {
label = "led4";
gpios = <&gpm4 3 GPIO_ACTIVE_LOW>;
default-state = "off";
linux,default-trigger = "mmc0";
};
};本次主要分析led1：
compatible = "gpio-leds";主要匹配：./drivers/leds/leds-gpio.c
static const struct of_device_id of_gpio_leds_match[] = {
{ .compatible = "gpio-leds", },
{},
};led在probe时，将设备树中的匹配到的节点全部进行初始化。
属性
label在下面解释：static struct gpio_leds_priv *gpio_leds_create(struct platform_device *pdev) { ret = fwnode_property_read_string(child, "label", &led.name); }- 属性
gpios在下面解释：
static struct gpio_leds_priv *gpio_leds_create(struct platform_device *pdev) { led.gpiod = devm_fwnode_get_gpiod_from_child(dev, NULL, child, GPIOD_ASIS, led.name); <-- devm_fwnode_get_index_gpiod_from_child <-- for (i = 0; i < ARRAY_SIZE(gpio_suffixes); i++) { if (con_id) snprintf(prop_name, sizeof(prop_name), "%s-%s", con_id, gpio_suffixes[i]); else snprintf(prop_name, sizeof(prop_name), "%s", gpio_suffixes[i]); desc = fwnode_get_named_gpiod(child, prop_name, index, flags, label); if (!IS_ERR(desc) || (PTR_ERR(desc) != -ENOENT)) break; } static const char * const gpio_suffixes[] = { "gpios", "gpio" }; 也就是说属性gpios也可以写成gpio,内核也可以识别 }- 属性
default-state = "off"在下面解释：
static struct gpio_leds_priv *gpio_leds_create(struct platform_device *pdev) { if (!fwnode_property_read_string(child, "default-state", &state)) { if (!strcmp(state, "keep")) led.default_state = LEDS_GPIO_DEFSTATE_KEEP; else if (!strcmp(state, "on")) led.default_state = LEDS_GPIO_DEFSTATE_ON; else led.default_state = LEDS_GPIO_DEFSTATE_OFF; } }- 属性
linux,default-trigger在下面解释：
static struct gpio_leds_priv *gpio_leds_create(struct platform_device *pdev) { fwnode_property_read_string(child, "linux,default-trigger", &led.default_trigger); }- 属性
menuconfig
root@ubuntu:/opt/linux-4.12# make menuconfig
Device Drivers --->
[*] LED Support --->
<*> LED Class Support
<*> LED Support for GPIO connected LEDs
[*] LED Trigger support --->
<*> LED Heartbeat Trigger支持三种配置方式：
< >：不支持
<*>：编译进内核
分析驱动
我们采用从后向前分析的方式，我们的目的是让LED1实现心跳，首先要找到实现心跳的驱动位置：
./drivers/leds/trigger/ledtrig-heartbeat.c
module_init(heartbeat_trig_init); -->static int __init heartbeat_trig_init(void)
{
int rc = led_trigger_register(&heartbeat_led_trigger);
if (!rc) {
atomic_notifier_chain_register(&panic_notifier_list,
&heartbeat_panic_nb);
register_reboot_notifier(&heartbeat_reboot_nb);
}
return rc;
}
static struct led_trigger heartbeat_led_trigger = {
.name = "heartbeat",
.activate = heartbeat_trig_activate,
.deactivate = heartbeat_trig_deactivate,
};而led_trigger_register在./drivers/leds/led-triggers.c中定义。
int led_trigger_register(struct led_trigger *trig)
{
...
/* Add to the list of led triggers */
list_add_tail(&trig->next_trig, &trigger_list);
[1] 这样 heartbeat_led_trigger 被添加到链表中，通过name字段来标识
/* Register with any LEDs that have this as a default trigger */
list_for_each_entry(led_cdev, &leds_list, node) {
down_write(&led_cdev->trigger_lock);
if (!led_cdev->trigger && led_cdev->default_trigger &&
!strcmp(led_cdev->default_trigger, trig->name))
led_trigger_set(led_cdev, trig);
up_write(&led_cdev->trigger_lock);
}
[2] 遍历leds_list链表，那么肯定有地方要添加元素到链表，找到函数
leds_list <--
of_led_classdev_register <--
devm_of_led_classdev_register <--
create_gpio_led <--
gpio_led_probe <--
static struct platform_driver gpio_led_driver = {
.probe = gpio_led_probe,
.shutdown = gpio_led_shutdown,
.driver = {
.name = "leds-gpio",
.of_match_table = of_gpio_leds_match,
},
};
module_platform_driver(gpio_led_driver); <--
/* module_platform_driver() - Helper macro for drivers that don't do
* anything special in module init/exit. This eliminates a lot of
* boilerplate. Each module may only use this macro once, and
* calling it replaces module_init() and module_exit()
*/
#define module_platform_driver(__platform_driver) \
module_driver(__platform_driver, platform_driver_register, \
platform_driver_unregister)
}
[1]
struct led_trigger {
/* Trigger Properties */
const char *name;
void (*activate)(struct led_classdev *led_cdev);
void (*deactivate)(struct led_classdev *led_cdev);
/* LEDs under control by this trigger (for simple triggers) */
rwlock_t leddev_list_lock;
struct list_head led_cdevs;
/* Link to next registered trigger */
struct list_head next_trig;
};
[2]
./drivers/leds/led-class.c
int of_led_classdev_register(struct device *parent, struct device_node *np,
struct led_classdev *led_cdev)
{
...
list_add_tail(&led_cdev->node, &leds_list);
}我们在顺序执行流程整理一下：[分支A]
module_platform_driver(gpio_led_driver);
gpio_led_driver -->
gpio_led_probe -->
gpio_leds_create -->
create_gpio_led -->
devm_of_led_classdev_register -->
of_led_classdev_register -->
list_add_tail(&led_cdev->node, &leds_list); # leds_list链表产生了节点再来看另一个分支：[分支B]
module_init(heartbeat_trig_init);
heartbeat_trig_init -->
led_trigger_register -->
list_for_each_entry(led_cdev, &leds_list, node) {
down_write(&led_cdev->trigger_lock);
if (!led_cdev->trigger && led_cdev->default_trigger &&
!strcmp(led_cdev->default_trigger, trig->name))
led_trigger_set(led_cdev, trig);
up_write(&led_cdev->trigger_lock);
} # 遍历leds_list链表这样两个分支便产生了关联，分支A先执行，然后分支B执行。其实也很好理解，分支A在做底层的初始化和配置工作，分支B是中间接口层，向下连接底层驱动，向上提供访问接口。
如果要控制LED，需要调用函数：
static struct led_trigger heartbeat_led_trigger = {
.name = "heartbeat",
.activate = heartbeat_trig_activate,
.deactivate = heartbeat_trig_deactivate,
};通过搜索，找到./drivers/leds/led-triggers.c中的函数：
void led_trigger_set(struct led_classdev *led_cdev, struct led_trigger *trig)
{
if (led_cdev->trigger) {
write_lock_irqsave(&led_cdev->trigger->leddev_list_lock, flags);
list_del(&led_cdev->trig_list);
write_unlock_irqrestore(&led_cdev->trigger->leddev_list_lock,
flags);
cancel_work_sync(&led_cdev->set_brightness_work);
led_stop_software_blink(led_cdev);
if (led_cdev->trigger->deactivate) # 使无效
led_cdev->trigger->deactivate(led_cdev);
led_cdev->trigger = NULL;
led_set_brightness(led_cdev, LED_OFF);
}
if (trig) {
write_lock_irqsave(&trig->leddev_list_lock, flags);
list_add_tail(&led_cdev->trig_list, &trig->led_cdevs);
write_unlock_irqrestore(&trig->leddev_list_lock, flags);
led_cdev->trigger = trig;
if (trig->activate) # 使生效
trig->activate(led_cdev);
}
}搜索led_trigger_set的调用者：
ssize_t led_trigger_store(struct device *dev, struct device_attribute *attr,
const char *buf, size_t count)
{
led_trigger_set(led_cdev, trig);
}搜索led_trigger_store的调用者：
#ifdef CONFIG_LEDS_TRIGGERS
static DEVICE_ATTR(trigger, 0644, led_trigger_show, led_trigger_store);
static struct attribute *led_trigger_attrs[] = {
&dev_attr_trigger.attr,
NULL,
};
static const struct attribute_group led_trigger_group = {
.attrs = led_trigger_attrs,
};
#endif
参考[1]，上述代码可以修改为以下形式：
static device_attribute dev_attr_trigger = {
.attr = {.trigger = __stringify(trigger), \
.mode = VERIFY_OCTAL_PERMISSIONS(0644) }, \
.show = led_trigger_show, \
.store = led_trigger_store, \
};
static struct attribute *led_trigger_attrs[] = {
&dev_attr_trigger.attr,
NULL,
};
static const struct attribute_group led_trigger_group = {
.attrs = led_trigger_attrs,
};
[1]
#define DEVICE_ATTR(_name, _mode, _show, _store) \
struct device_attribute dev_attr_##_name = __ATTR(_name, _mode, _show, _store)
#define __ATTR(_name, _mode, _show, _store) { \
.attr = {.name = __stringify(_name), \
.mode = VERIFY_OCTAL_PERMISSIONS(_mode) }, \
.show = _show, \
.store = _store, \
}搜索led_trigger_group调用者：
static const struct attribute_group *led_groups[] = {
&led_group,
#ifdef CONFIG_LEDS_TRIGGERS
&led_trigger_group,
#endif
NULL,
};搜索led_groups调用者：
static int __init leds_init(void)
{
leds_class = class_create(THIS_MODULE, "leds");
if (IS_ERR(leds_class))
return PTR_ERR(leds_class);
leds_class->pm = &leds_class_dev_pm_ops;
leds_class->dev_groups = led_groups;
return 0;
}
subsys_initcall(leds_init);再次总结：led-class.c为led类向外提供的通用接口，调用顺序：
module_platform_driver(gpio_led_driver); --> # ./drivers/leds/leds-gpio.c
module_init(heartbeat_trig_init); --> # ./drivers/leds/trigger/heartbeat.c
led_trigger_set(); --> # ./drivers/leds/led-triggers.c
subsys_initcall(leds_init); --> # ./drivers/leds/led-class.c对于LED心跳来说，咚咚两下，就是说需要使用状态机驱动，在切换状态时，修改定时器的定时周期即可。
最核心的执行体为：led_heartbeat_function
创建定时器：
static void heartbeat_trig_activate(struct led_classdev *led_cdev)
{
setup_timer(&heartbeat_data->timer,
led_heartbeat_function, (unsigned long) led_cdev);
}只执行一次，将led_heartbeat_function作为定时器溢出的回调函数，用来切换状态机。
修改定时器：
static void led_heartbeat_function(unsigned long data)
{
mod_timer(&heartbeat_data->timer, jiffies + delay);
}每次定时器溢出，执行一次。
关闭定时器：
static void heartbeat_trig_deactivate(struct led_classdev *led_cdev)
{
del_timer_sync(&heartbeat_data->timer);
}永远不会执行，心跳永远不会停止。
LED打开时机：
led_trigger_store -->
ssize_t led_trigger_store(struct device *dev, struct device_attribute *attr,
const char *buf, size_t count)
{
list_for_each_entry(trig, &trigger_list, next_trig) {
if (sysfs_streq(buf, trig->name)) {
down_write(&led_cdev->trigger_lock);
led_trigger_set(led_cdev, trig); -->
up_write(&led_cdev->trigger_lock);
up_read(&triggers_list_lock);
goto unlock;
}
}
}
void led_trigger_set(struct led_classdev *led_cdev, struct led_trigger *trig)
{
if (trig) {
write_lock_irqsave(&trig->leddev_list_lock, flags);
list_add_tail(&led_cdev->trig_list, &trig->led_cdevs);
write_unlock_irqrestore(&trig->leddev_list_lock, flags);
led_cdev->trigger = trig;
if (trig->activate)
trig->activate(led_cdev); -->
}
}
static void heartbeat_trig_activate(struct led_classdev *led_cdev)
{
setup_timer(&heartbeat_data->timer,
led_heartbeat_function, (unsigned long) led_cdev); --> # Open HeartBeat
led_heartbeat_function(heartbeat_data->timer.data);
}
设备位置
LED 会在 /sys/bus/platform/devices/leds/leds/ 目录生成文件。读写文件可以操作 LED 设备了。
查看触发器：
[root@TINY4412:~]# cat /sys/bus/platform/devices/leds/leds/led4/trigger
none kbd-scrolllock kbd-numlock kbd-capslock kbd-kanalock kbd-shiftlock kbd-altgrlock kbd-ctrllock kbd-altlock kbd-shiftllock kbd-shiftrlock kbd-ctrlllock kbd-ctrlrlock usbport usb-gadget usb-host [mmc0] mmc1 heartbeat [xxx] 表示当前触发器被选中，当前设备被读写时， LED 会有相应动作。
LED4 的触发器为 mmc0 ，mmc0 表示 SD卡。 当我们拔掉 SD卡 时， LED4 开始闪烁。
上述列表中的触发器都是可以配置的。