在《Linux内核自带的leds-gpio代码分析 - 电子网 (dianziwang.net)》这篇文章中有介绍当一个新的LED的驱动被加载后，如果对应的平台设备和平台驱动匹配，就会执行驱动中的probe函数。添加完LED的字符设备后，会遍历触发器链表，比较是否有名字相同的触发器与设备树中给的触发器名字是否相同，如果相同就会调用触发器的active函数。
好，那这里我们就先以ledtrig-timer.c来分析：
假如我们的设备树文件中启用了这个触发器：linux,default-trigger = "timer";
leds: leds {
compatible = "gpio-leds";
rgb_led_r: rgb-led-r {
gpios = <&gpio1 RK_PB2 GPIO_ACTIVE_LOW>;
linux,default-trigger = "timer";
linux,delay-reg = <0>; // 延时注册
linux,blink-delay-on = <500>; // 打开时间
linux,blink-delay-off = <500>; // 关闭时间
};
rgb_led_g: rgb-led-g {
gpios = <&gpio1 RK_PB1 GPIO_ACTIVE_LOW>;
linux,default-trigger = "timer";
linux,delay-reg = <100>; // 延时注册
linux,blink-delay-on = <1000>;
linux,blink-delay-off = <1000>;
};
rgb_led_b: rgb-led-b {
gpios = <&gpio1 RK_PB0 GPIO_ACTIVE_LOW>;
linux,default-trigger = "timer";
linux,delay-reg = <100>; // 延时注册
linux,blink-delay-on = <1500>;
linux,blink-delay-off = <1500>;
};
};调用触发器的active函数：
static void timer_trig_activate(struct led_classdev *led_cdev)
{
int rc;
led_cdev->trigger_data = NULL;
rc = device_create_file(led_cdev->dev, &dev_attr_delay_on);
if (rc)
return;
rc = device_create_file(led_cdev->dev, &dev_attr_delay_off);
if (rc)
goto err_out_delayon;
led_blink_set(led_cdev, &led_cdev->blink_delay_on,
&led_cdev->blink_delay_off);
led_cdev->activated = true;
return;
err_out_delayon:
device_remove_file(led_cdev->dev, &dev_attr_delay_on);
}这里首先在LED的sys目录下添加了两个属性文件，然后调用led_blink_set来设置亮和灭的时间。
这两个属性文件又来源于上面的定义：
static DEVICE_ATTR(delay_on, 0644, led_delay_on_show, led_delay_on_store);
static DEVICE_ATTR(delay_off, 0644, led_delay_off_show, led_delay_off_store);
static struct attribute *timer_trig_attrs[] = {
&dev_attr_delay_on.attr,
&dev_attr_delay_off.attr,
NULL
};
ATTRIBUTE_GROUPS(timer_trig);我们看下DEVICE_ATTR是什么？
内核根目录/include/linux/device.h文件中有定义：
#define DEVICE_ATTR(_name, _mode, _show, _store) \ struct device_attribute dev_attr_##_name = __ATTR(_name, _mode, _show, _store)
在Documentation/driver-model/device.txt文档中有对于这个的介绍：
ˉˉˉˉˉˉˉˉˉˉˉˉˉ
Attributes are declared using a macro called DEVICE_ATTR：
#define DEVICE_ATTR(name, mode, show, store)
意思是说，宏 DEVICE_ATTR 用来声明 设备属性文件的 属性（听起来像绕口令）。宏的各参数含义如下：
name 属性文件的名称
mode 属性文件的权限。这个权限值为类似于 0644 这样的 4 位数，分别表示 SUID/GUID+User+Group+Others
show 从该属性文件读数据时调用的函数
store 向该属性文件写数据时调用的函数 宏 __ATTR(_name, _mode, _show, _store) 的定义：
#define __ATTR(_name, _mode, _show, _store) { \
.attr = {.name = __stringify(_name), .mode = _mode }, \
.show = _show, \
.store = _store, \
}结构体 device_attribute 的定义：
struct device_attribute {
struct attribute attr;
ssize_t (*show)(struct device *dev, struct device_attribute *attr, char *buf);
ssize_t (*store)(struct device *dev, struct device_attribute *attr, const char *buf, size_t count);
};
由此可见， 宏 DEVICE_ATTR的作用实际上是在声明并初始化一个 device_attribute结构体。
该结构体名称为 dev_attr_##_name （这里使用了预处理命令中 粘贴操作符 的概念）。
回到我们LED定时器触发这里，我们把 static DEVICE_ATTR(delay_on, 0644, led_delay_on_show, led_delay_on_store); 展开：
struct device_attribute dev_attr_delay_on = __ATTR(delay_on, 0644, led_delay_on_show, led_delay_on_store)
进一步展开得到：
struct device_attribute dev_attr_delay_on = { \
.attr = {.name = __stringify(delay_on), .mode = 0644}, \
.show = led_delay_on_show, \
.store = led_delay_on_store, \
}同理，我们把 static DEVICE_ATTR(delay_off, 0644, led_delay_off_show, led_delay_off_store);展开：
struct device_attribute dev_attr_delay_off = __ATTR(delay_off, 0644, led_delay_off_show, led_delay_off_store)
进一步展开得到：
struct device_attribute dev_attr_delay_off = { \
.attr = {.name = __stringify(delay_off), .mode = 0644}, \
.show = led_delay_off_show, \
.store = led_delay_off_store, \
}这两个属性放到了一个属性组里，我们来看下这个属性组，也是个宏定义：
static struct attribute *timer_trig_attrs[] = {
&dev_attr_delay_on.attr,
&dev_attr_delay_off.attr,
NULL
};
ATTRIBUTE_GROUPS(timer_trig);ATTRIBUTE_GROUPS的原型在include\linux\sysfs.h：
#define __ATTRIBUTE_GROUPS(_name) \
static const struct attribute_group *_name##_groups[] = { \
&_name##_group, \
NULL, \
}
#define ATTRIBUTE_GROUPS(_name) \
static const struct attribute_group _name##_group = { \
.attrs = _name##_attrs, \
}; \
__ATTRIBUTE_GROUPS(_name)展开就是：
#define __ATTRIBUTE_GROUPS(timer_trig) \
static const struct attribute_group *timer_trig_groups[] = { \
&timer_trig_group, \
NULL, \ } #define ATTRIBUTE_GROUPS(timer_trig) \
static const struct attribute_group timer_trig_group = { \
.attrs = timer_trig_attrs, \
}; \ __ATTRIBUTE_GROUPS(timer_trig)
那这些属性文件到底在哪里创建呢？我们来分析一下看看是不是这样的，当我们注册触发器的时候会与LED设备链表中的设备节点中的触发器名字做比较，如果相同就会设置触发器，进而创建相关的属性文件。
module_led_trigger(timer_led_trigger);
module_driver(__led_trigger, led_trigger_register, \ led_trigger_unregister)
int led_trigger_register(struct led_trigger *trig)
{
struct led_classdev *led_cdev;
struct led_trigger *_trig;
rwlock_init(&trig->leddev_list_lock);
INIT_LIST_HEAD(&trig->led_cdevs);
down_write(&triggers_list_lock);
/* Make sure the trigger's name isn't already in use */
list_for_each_entry(_trig, &trigger_list, next_trig) {
if (!strcmp(_trig->name, trig->name)) {
up_write(&triggers_list_lock);
return -EEXIST;
}
}
/* Add to the list of led triggers */
list_add_tail(&trig->next_trig, &trigger_list);
up_write(&triggers_list_lock);
/* Register with any LEDs that have this as a default trigger */
down_read(&leds_list_lock);
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);
}
up_read(&leds_list_lock);
return 0;
}这里把该触发器挂到了触发器列表，然后与LED设备列表里的节点比较触发器的名字，如果匹配则设置这个LED设备的触发器。
int led_trigger_set(struct led_classdev *led_cdev, struct led_trigger *trig)
{
unsigned long flags;
char *event = NULL;
char *envp[2];
const char *name;
int ret;
if (!led_cdev->trigger && !trig)
return 0;
name = trig ? trig->name : "none";
event = kasprintf(GFP_KERNEL, "TRIGGER=%s", name);
/* Remove any existing trigger */
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)
led_cdev->trigger->deactivate(led_cdev);
device_remove_groups(led_cdev->dev, led_cdev->trigger->groups);
led_cdev->trigger = NULL;
led_cdev->trigger_data = NULL;
led_cdev->activated = false;
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)
ret = trig->activate(led_cdev);
else
ret = 0;
if (ret)
goto err_activate;
ret = device_add_groups(led_cdev->dev, trig->groups);
if (ret) {
dev_err(led_cdev->dev, "Failed to add trigger attributes\n");
goto err_add_groups;
}
}
if (event) {
envp[0] = event;
envp[1] = NULL;
if (kobject_uevent_env(&led_cdev->dev->kobj, KOBJ_CHANGE, envp))
dev_err(led_cdev->dev,
"%s: Error sending uevent\n", __func__);
kfree(event);
}
return 0;
err_add_groups:
if (trig->deactivate)
trig->deactivate(led_cdev);
err_activate:
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);
led_cdev->trigger = NULL;
led_cdev->trigger_data = NULL;
led_set_brightness(led_cdev, LED_OFF);
kfree(event);
return ret;
}trig->activate(led_cdev); 调用触发器的active函数，在本文开头已经介绍过了，这里不展开，我们看下面的device_add_groups(led_cdev->dev, trig->groups);接着调用了sysfs_create_groups(&dev->kobj, groups);
int sysfs_create_groups(struct kobject *kobj,
const struct attribute_group **groups)
{
int error = 0;
int i;
if (!groups)
return 0;
for (i = 0; groups[i]; i++) {
error = sysfs_create_group(kobj, groups[i]);
if (error) {
while (--i >= 0)
sysfs_remove_group(kobj, groups[i]);
break;
}
}
return error;
}这个groups就是timer_trig_groups,里面只有一个数组元素timer_trig_group
static const struct attribute_group *timer_trig_groups[] = { \
&timer_trig_group, \
NULL, \
}sysfs_create_group调用internal_create_group(kobj, 0, grp);
static int internal_create_group(struct kobject *kobj, int update,
const struct attribute_group *grp)
{
struct kernfs_node *kn;
kuid_t uid;
kgid_t gid;
int error;
BUG_ON(!kobj || (!update && !kobj->sd));
/* Updates may happen before the object has been instantiated */
if (unlikely(update && !kobj->sd))
return -EINVAL;
if (!grp->attrs && !grp->bin_attrs) {
WARN(1, "sysfs: (bin_)attrs not set by subsystem for group: %s/%s\n",
kobj->name, grp->name ?: "");
return -EINVAL;
}
kobject_get_ownership(kobj, &uid, &gid);
if (grp->name) {
if (update) {
kn = kernfs_find_and_get(kobj->sd, grp->name);
if (!kn) {
pr_warn("Can't update unknown attr grp name: %s/%s\n",
kobj->name, grp->name);
return -EINVAL;
}
} else {
kn = kernfs_create_dir_ns(kobj->sd, grp->name, //创建组目录
S_IRWXU | S_IRUGO | S_IXUGO,
uid, gid, kobj, NULL);
if (IS_ERR(kn)) {
if (PTR_ERR(kn) == -EEXIST)
sysfs_warn_dup(kobj->sd, grp->name);
return PTR_ERR(kn);
}
}
} else
kn = kobj->sd;
kernfs_get(kn);
error = create_files(kn, kobj, uid, gid, grp, update);//创建属性文件
if (error) {
if (grp->name)
kernfs_remove(kn);
}
kernfs_put(kn);
if (grp->name && update)
kernfs_put(kn);
return error;
}在这里面可以看到创建了组的目录和属性文件。
static int create_files(struct kernfs_node *parent, struct kobject *kobj,
kuid_t uid, kgid_t gid,
const struct attribute_group *grp, int update)
{
struct attribute *const *attr;
struct bin_attribute *const *bin_attr;
int error = 0, i;
if (grp->attrs) {
for (i = 0, attr = grp->attrs; *attr && !error; i++, attr++) {
umode_t mode = (*attr)->mode;
/*
* In update mode, we're changing the permissions or
* visibility. Do this by first removing then
* re-adding (if required) the file.
*/
if (update)
kernfs_remove_by_name(parent, (*attr)->name);
if (grp->is_visible) {
mode = grp->is_visible(kobj, *attr, i);
if (!mode)
continue;
}
WARN(mode & ~(SYSFS_PREALLOC | 0664),
"Attribute %s: Invalid permissions 0%o\n",
(*attr)->name, mode);
mode &= SYSFS_PREALLOC | 0664;
error = sysfs_add_file_mode_ns(parent, *attr, false,
mode, uid, gid, NULL);
if (unlikely(error))
break;
}
if (error) {
remove_files(parent, grp);
goto exit;
}
}
if (grp->bin_attrs) {
for (i = 0, bin_attr = grp->bin_attrs; *bin_attr; i++, bin_attr++) {
umode_t mode = (*bin_attr)->attr.mode;
if (update)
kernfs_remove_by_name(parent,
(*bin_attr)->attr.name);
if (grp->is_bin_visible) {
mode = grp->is_bin_visible(kobj, *bin_attr, i);
if (!mode)
continue;
}
WARN(mode & ~(SYSFS_PREALLOC | 0664),
"Attribute %s: Invalid permissions 0%o\n",
(*bin_attr)->attr.name, mode);
mode &= SYSFS_PREALLOC | 0664;
error = sysfs_add_file_mode_ns(parent,
&(*bin_attr)->attr, true,
mode,
uid, gid, NULL);
if (error)
break;
}
if (error)
remove_files(parent, grp);
}
exit:
return error;
}创建完后我们就可以在对应的LED的文件目录下看到两个属性文件：
root@RK356X:/# ls /sys/class/leds/ mmc0:: rgb-led-b rgb-led-g rgb-led-r root@RK356X:/# ls /sys/class/leds/rgb-led-b brightness delay_on max_brightness subsystem uevent delay_off device power trigger
我们看到还多出来一些属性文件，这些属性文件是在注册LED设备的时候随之自动创建的。
然后就可以在命令行中对这些属性文件进行读写操作：
定时触发 echo timer > /sys/class/leds/rgb-led-b/trigger echo 5000 > /sys/class/leds/rgb-led-b/delay_on echo 5000 > /sys/class/leds/rgb-led-b/delay_off 心跳触发 echo heartbeat > /sys/class/leds/rgb-led-b/trigger echo 100 > /sys/class/leds/rgb-led-b/delay_on echo 200 > /sys/class/leds/rgb-led-b/delay_off 亮灭控制 echo 0 > /sys/class/leds/rgb-led-b/brightness 亮 echo 1 > /sys/class/leds/rgb-led-b/brightness 灭echo timer > /sys/class/leds/led1/trigger 这一句会调用 led_trigger_store()-> led_trigger_set()-> trigger->activate(led_cdev); 从而调用ledtrig-timer.c文件里的timer_trig_activate()
echo 100 > /sys/class/leds/reb-led-b/deay_on 这一句会调用led_delay_on_store -> led_blink_set(led_cdev, &state, &led_cdev->blink_delay_off); 来设置闪烁关闭的时间
#关闭蓝灯 实际是移除了存在的触发器，并把亮度设置成关闭 led_trigger_remove=》led_trigger_set(led_cdev, NULL);=》led_set_brightness(led_cdev, LED_OFF); rk3566_tspi:/ # echo "none" > /sys/class/leds/rgb-led-b/trigger #关闭绿灯 rk3566_tspi:/ # echo "none" > /sys/class/leds/rgb-led-g/trigger #关闭红灯 rk3566_tspi:/ # echo "none" > /sys/class/leds/rgb-led-r/trigger
#常亮蓝灯 添加ledtrig-timer.c这个触发器，在defon_trig_activate=》led_set_brightness_nosleep(led_cdev, led_cdev->max_brightness);设置为最大亮度 rk3566_tspi:/ # echo "default-on" > /sys/class/leds/rgb-led-b/trigger #常亮绿灯 rk3566_tspi:/ # echo "default-on" > /sys/class/leds/rgb-led-g/trigger #常亮红灯 rk3566_tspi:/ # echo "default-on" > /sys/class/leds/rgb-led-r/trigger
#常亮蓝灯 rk3566_tspi:/ # echo "heartbeat" > /sys/class/leds/rgb-led-b/trigger #常亮绿灯 rk3566_tspi:/ # echo "heartbeat" > /sys/class/leds/rgb-led-g/trigger #常亮红灯 rk3566_tspi:/ # echo "heartbeat" > /sys/class/leds/rgb-led-r/trigger
#常亮蓝灯 rk3566_tspi:/ # echo "timer" > /sys/class/leds/rgb-led-b/trigger #常亮绿灯 rk3566_tspi:/ # echo "timer" > /sys/class/leds/rgb-led-g/trigger #常亮红灯 rk3566_tspi:/ # echo "timer" > /sys/class/leds/rgb-led-r/trigger
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