以树莓派为例子，分析一下其中LED的 platform device 和 platform driver.
查看LED设备，被挂载在/sys/devices/platform下。
注意其中的driver指向，
driver -> ../../../bus/platform/drivers/leds-gpio
pi@raspberrypi:/sys/devices/platform/leds $ tree
.
├── driver -> ../../../bus/platform/drivers/leds-gpio
├── driver_override
├── leds
│ ├── led0
│ │ ├── brightness
│ │ ├── device -> ../../../leds
│ │ ├── max_brightness
│ │ ├── power
│ │ │ ├── autosuspend_delay_ms
│ │ │ ├── control
│ │ │ ├── runtime_active_time
│ │ │ ├── runtime_status
│ │ │ └── runtime_suspended_time
│ │ ├── subsystem -> ../../../../../class/leds
│ │ ├── trigger
│ │ └── uevent
│ └── led1
│ ├── brightness
│ ├── device -> ../../../leds
│ ├── max_brightness
│ ├── power
│ │ ├── autosuspend_delay_ms
│ │ ├── control
│ │ ├── runtime_active_time
│ │ ├── runtime_status
│ │ └── runtime_suspended_time
│ ├── subsystem -> ../../../../../class/leds
│ ├── trigger
│ └── uevent
├── modalias
├── of_node -> ../../../firmware/devicetree/base/leds
├── power
│ ├── autosuspend_delay_ms
│ ├── control
│ ├── runtime_active_time
│ ├── runtime_status
│ └── runtime_suspended_time
├── subsystem -> ../../../bus/platform
└── uevent同样，在/sys/bus/platform/drivers/leds-gpio下可以看到其中的leds指向了leds设备
pi@raspberrypi:/sys/bus/platform/drivers/leds-gpio $ tree
.
├── bind
├── leds -> ../../../../devices/platform/leds
├── uevent
└── unbind驱动leds-gpio.c
查看驱动，linuxdriversledsleds-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;
else
level = 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->cdev.flags & SET_GPIO_INPUT) {
gpiod_direction_input(led_dat->gpiod);
led_dat->cdev.flags &= ~SET_GPIO_INPUT;
} else if (led_dat->cdev.flags & SET_GPIO_OUTPUT) {
gpiod_direction_output(led_dat->gpiod, level);
led_dat->cdev.flags &= ~SET_GPIO_OUTPUT;
} else {
if (led_dat->can_sleep ||
(led_dat->cdev.flags & (SET_GPIO_INPUT | SET_GPIO_OUTPUT) ))
gpiod_set_value_cansleep(led_dat->gpiod, level);
else
gpiod_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);
return 0;
}
static enum led_brightness gpio_led_get(struct led_classdev *led_cdev)
{
struct gpio_led_data *led_dat =
container_of(led_cdev, struct gpio_led_data, cdev);
return gpiod_get_value_cansleep(led_dat->gpiod) ? LED_FULL : LED_OFF;
}
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);
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;
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)
",
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;
led_dat->cdev.default_trigger = template->default_trigger;
led_dat->can_sleep = gpiod_cansleep(led_dat->gpiod);
if (!led_dat->can_sleep)
led_dat->cdev.brightness_set = gpio_led_set;
else
led_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;
}
led_dat->cdev.brightness_get = gpio_led_get;
if (template->default_state == LEDS_GPIO_DEFSTATE_KEEP) {
state = gpiod_get_value_cansleep(led_dat->gpiod);
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);
if (ret < 0)
return ret;
return devm_of_led_classdev_register(parent, np, &led_dat->cdev);
}
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) {
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);
if (ret && IS_ENABLED(CONFIG_OF) && np)
led.name = np->name;
if (!led.name) {
fwnode_handle_put(child);
return ERR_PTR(-EINVAL);
}
led.gpiod = devm_fwnode_get_gpiod_from_child(dev, NULL, child,
GPIOD_ASIS,
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;
else
led.default_state = LEDS_GPIO_DEFSTATE_OFF;
}
if (fwnode_property_present(child, "retain-state-suspended"))
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", },
{},
};
MODULE_DEVICE_TABLE(of, of_gpio_leds_match);
static int gpio_led_probe(struct platform_device *pdev)
{
struct gpio_led_platform_data *pdata = dev_get_platdata(&pdev->dev);
struct gpio_leds_priv *priv;
int i, ret = 0;
if (pdata && pdata->num_leds) {
priv = devm_kzalloc(&pdev->dev,
sizeof_gpio_leds_priv(pdata->num_leds),
GFP_KERNEL);
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);
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 = {
.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_AUTHOR("Raphael Assenat <raph@8d.com>, Trent Piepho <tpiepho@freescale.com>");
MODULE_DESCRIPTION("GPIO LED driver");
MODULE_LICENSE("GPL");
MODULE_ALIAS("platform:leds-gpio");
注册platform device
在树莓派的系统中是通过设备树来注册leds设备的
在bcm2708-rpi.dtsi中
leds: leds {
compatible = "gpio-leds";
};在bcm2709-rpi-2-b.dts
&leds {
act_led: act {
label = "led0";
linux,default-trigger = "mmc0";
gpios = <&gpio 47 0>;
};
pwr_led: pwr {
label = "led1";
linux,default-trigger = "input";
gpios = <&gpio 35 0>;
};
};参考：
https://blog.csdn.net/zqixiao_09/article/details/50889458
https://blog.csdn.net/subfate/article/details/53494926
https://blog.csdn.net/jklinux/article/details/78645106