前言

设备树LED部分中显示

compatible = "gpio-leds";

与/drivers/leds/leds-gpio.c的compatible字样一致，且SDK也指出采用该驱动文件。

leds-gpio.c

/** LEDs driver for GPIOs** Copyright (C) 2007 8D Technologies inc.* Raphael Assenat <raph@8d.com>* Copyright (C) 2008 Freescale Semiconductor, Inc.** This program is free software; you can redistribute it and/or modify* it under the terms of the GNU General Public License version 2 as* published by the Free Software Foundation.**/
#include <linux/err.h>
#include <linux/gpio.h>
#include <linux/gpio/consumer.h>
#include <linux/kernel.h>
#include <linux/leds.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/platform_device.h>
#include <linux/property.h>
#include <linux/slab.h>struct gpio_led_data {struct led_classdev cdev;struct gpio_desc *gpiod;u8 can_sleep;u8 blinking;gpio_blink_set_t platform_gpio_blink_set;
};static inline struct gpio_led_data *cdev_to_gpio_led_data(struct led_classdev *led_cdev)
{return container_of(led_cdev, struct gpio_led_data, cdev);
}static void gpio_led_set(struct led_classdev *led_cdev,enum led_brightness value)
{struct gpio_led_data *led_dat = cdev_to_gpio_led_data(led_cdev);int level;if (value == LED_OFF)level = 0;elselevel = 1;if (led_dat->blinking) {led_dat->platform_gpio_blink_set(led_dat->gpiod, level,NULL, NULL);led_dat->blinking = 0;} else {if (led_dat->can_sleep)gpiod_set_value_cansleep(led_dat->gpiod, level);elsegpiod_set_value(led_dat->gpiod, level);}
}static int gpio_led_set_blocking(struct led_classdev *led_cdev,enum led_brightness value)
{gpio_led_set(led_cdev, value); //设置gpio值return 0;
}static int gpio_blink_set(struct led_classdev *led_cdev,unsigned long *delay_on, unsigned long *delay_off)
{struct gpio_led_data *led_dat = cdev_to_gpio_led_data(led_cdev); //通过container_of 获取 gpio_led_data结构体led_dat->blinking = 1;return led_dat->platform_gpio_blink_set(led_dat->gpiod, GPIO_LED_BLINK,delay_on, delay_off);
}static int create_gpio_led(const struct gpio_led *template,struct gpio_led_data *led_dat, struct device *parent,struct device_node *np, gpio_blink_set_t blink_set)
{int ret, state;led_dat->gpiod = template->gpiod; //获取对应的gpio_desc结构体if (!led_dat->gpiod) {/** This is the legacy code path for platform code that* still uses GPIO numbers. Ultimately we would like to get* rid of this block completely.*/unsigned long flags = GPIOF_OUT_INIT_LOW;/* skip leds that aren't available */if (!gpio_is_valid(template->gpio)) {dev_info(parent, "Skipping unavailable LED gpio %d (%s)\n",template->gpio, template->name);return 0;}if (template->active_low)flags |= GPIOF_ACTIVE_LOW;ret = devm_gpio_request_one(parent, template->gpio, flags,template->name);if (ret < 0)return ret;led_dat->gpiod = gpio_to_desc(template->gpio);if (!led_dat->gpiod)return -EINVAL;}led_dat->cdev.name = template->name; //对应设备树的labelled_dat->cdev.default_trigger = template->default_trigger; //对应设备树的default_triggerled_dat->can_sleep = gpiod_cansleep(led_dat->gpiod); //查看可否sleepif (!led_dat->can_sleep) //针对gpio不能sleepled_dat->cdev.brightness_set = gpio_led_set; //绑定函数elseled_dat->cdev.brightness_set_blocking = gpio_led_set_blocking;led_dat->blinking = 0;if (blink_set) {led_dat->platform_gpio_blink_set = blink_set;led_dat->cdev.blink_set = gpio_blink_set; //绑定函数}if (template->default_state == LEDS_GPIO_DEFSTATE_KEEP) { //对应设备树的default statestate = gpiod_get_value_cansleep(led_dat->gpiod); //获取值if (state < 0)return state;} else {state = (template->default_state == LEDS_GPIO_DEFSTATE_ON);}led_dat->cdev.brightness = state ? LED_FULL : LED_OFF;if (!template->retain_state_suspended)led_dat->cdev.flags |= LED_CORE_SUSPENDRESUME;if (template->panic_indicator)led_dat->cdev.flags |= LED_PANIC_INDICATOR;if (template->retain_state_shutdown)led_dat->cdev.flags |= LED_RETAIN_AT_SHUTDOWN;ret = gpiod_direction_output(led_dat->gpiod, state); //设置方向为输出if (ret < 0)return ret;return devm_of_led_classdev_register(parent, np, &led_dat->cdev); //注册该class设备
}//用户可定义私有数据
struct gpio_leds_priv {int num_leds;struct gpio_led_data leds[];
};static inline int sizeof_gpio_leds_priv(int num_leds)
{return sizeof(struct gpio_leds_priv) +(sizeof(struct gpio_led_data) * num_leds);
}static struct gpio_leds_priv *gpio_leds_create(struct platform_device *pdev)
{struct device *dev = &pdev->dev;struct fwnode_handle *child;struct gpio_leds_priv *priv;int count, ret;count = device_get_child_node_count(dev);if (!count)return ERR_PTR(-ENODEV);priv = devm_kzalloc(dev, sizeof_gpio_leds_priv(count), GFP_KERNEL);if (!priv)return ERR_PTR(-ENOMEM);device_for_each_child_node(dev, child) { //对所有子节点遍历struct gpio_led_data *led_dat = &priv->leds[priv->num_leds];struct gpio_led led = {};const char *state = NULL;struct device_node *np = to_of_node(child);ret = fwnode_property_read_string(child, "label", &led.name); //从child节点的label读取字符串并存到led.name中if (ret && IS_ENABLED(CONFIG_OF) && np)led.name = np->name;if (!led.name) {fwnode_handle_put(child);//对该子节点放弃控制return ERR_PTR(-EINVAL);}//获取gpio_descled.gpiod = devm_fwnode_get_gpiod_from_child(dev, NULL, child,GPIOD_ASIS, //保持现状led.name);if (IS_ERR(led.gpiod)) {fwnode_handle_put(child); return ERR_CAST(led.gpiod);}fwnode_property_read_string(child, "linux,default-trigger",&led.default_trigger);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;elseled.default_state = LEDS_GPIO_DEFSTATE_OFF;}if (fwnode_property_present(child, "retain-state-suspended")) //检查是否有该信息定义led.retain_state_suspended = 1;if (fwnode_property_present(child, "retain-state-shutdown"))led.retain_state_shutdown = 1;if (fwnode_property_present(child, "panic-indicator"))led.panic_indicator = 1;ret = create_gpio_led(&led, led_dat, dev, np, NULL);if (ret < 0) {fwnode_handle_put(child);return ERR_PTR(ret);}led_dat->cdev.dev->of_node = np;priv->num_leds++;}return priv;
}static const struct of_device_id of_gpio_leds_match[] = {{ .compatible = "gpio-leds", }, //设备树上定义的compatible{},
};MODULE_DEVICE_TABLE(of, of_gpio_leds_match);//配对成功后，运行probe函数进行设备初始化
static int gpio_led_probe(struct platform_device *pdev)
{struct gpio_led_platform_data *pdata = dev_get_platdata(&pdev->dev); //获取该设备的led_platform结构体struct gpio_leds_priv *priv; //私有数据int i, ret = 0;// num_leds对应设备树中的子节点，此处应该为4，但我们的设备树应该调用else分支if (pdata && pdata->num_leds) {priv = devm_kzalloc(&pdev->dev,sizeof_gpio_leds_priv(pdata->num_leds),GFP_KERNEL);  //为私有数据分配数据if (!priv)return -ENOMEM;priv->num_leds = pdata->num_leds;for (i = 0; i < priv->num_leds; i++) {ret = create_gpio_led(&pdata->leds[i], &priv->leds[i],&pdev->dev, NULL,pdata->gpio_blink_set);if (ret < 0)return ret;}} else {priv = gpio_leds_create(pdev);if (IS_ERR(priv))return PTR_ERR(priv);}platform_set_drvdata(pdev, priv); //为该platform设备绑定私有数据return 0;
}static void gpio_led_shutdown(struct platform_device *pdev)
{struct gpio_leds_priv *priv = platform_get_drvdata(pdev);int i;for (i = 0; i < priv->num_leds; i++) {struct gpio_led_data *led = &priv->leds[i];if (!(led->cdev.flags & LED_RETAIN_AT_SHUTDOWN))gpio_led_set(&led->cdev, LED_OFF);}
}static struct platform_driver gpio_led_driver = {  //绑定platform driver相关.probe		= gpio_led_probe,  .shutdown	= gpio_led_shutdown,.driver		= {.name	= "leds-gpio",.of_match_table = of_gpio_leds_match,  //设备树上compatible与该match table上的配对},
};module_platform_driver(gpio_led_driver); //注册该platform驱动MODULE_AUTHOR("Raphael Assenat <raph@8d.com>, Trent Piepho <tpiepho@freescale.com>");
MODULE_DESCRIPTION("GPIO LED driver");
MODULE_LICENSE("GPL");
MODULE_ALIAS("platform:leds-gpio");