gpio_request()简单分析

一、软件环境

Andorid Version：5.0

Cpu & Arch：Intel X86_64

二、File Path

include/linux/gpio.h

include/asm-generic/gpio.h

drivers/gpio/gpiolib.c

三、代码分析

 

int gpio_request(unsigned gpio, const char *label){<span style="white-space:pre"></span>return gpiod_request(gpio_to_desc(gpio), label);}EXPORT_SYMBOL_GPL(gpio_request);

（1）根据gpio序号获取相应的描述gpio的结构体desc

static struct gpio_desc *gpio_to_desc(unsigned gpio){                                                                                                                                                 //<span style="font-family: Arial, Helvetica, sans-serif;">条件为真时(</span><span style="font-family: Arial, Helvetica, sans-serif;">0 <= gpio < ARCH_NR_GPIOS)输出Debug信息，且返回NULL</span>if (WARN(!gpio_is_valid(gpio), "invalid GPIO %d\n", gpio)) return NULL;elsereturn &gpio_desc[gpio];}

（2）根据desc与label，调用gpiod_request注册gpio口

static int gpiod_request(struct gpio_desc *desc, const char *label){struct gpio_chip*chip;intstatus = -EPROBE_DEFER;unsigned longflags;if (!desc) {pr_warn("%s: invalid GPIO\n", __func__);return -EINVAL;}spin_lock_irqsave(&gpio_lock, flags);chip = desc->chip;if (chip == NULL)goto done;if (!try_module_get(chip->owner))goto done;/* NOTE:  gpio_request() can be called in early boot, * before IRQs are enabled, for non-sleeping (SOC) GPIOs. */if (test_and_set_bit(FLAG_REQUESTED, &desc->flags) == 0) {//设置flags的第0位为1，并返回原来的值desc_set_label(desc, label ? : "?");status = 0;} else {status = -EBUSY;module_put(chip->owner);goto done;}if (chip->request) {/* chip->request may sleep */spin_unlock_irqrestore(&gpio_lock, flags);status = chip->request(chip, gpio_chip_hwgpio(desc));spin_lock_irqsave(&gpio_lock, flags);if (status < 0) {desc_set_label(desc, NULL);module_put(chip->owner);clear_bit(FLAG_REQUESTED, &desc->flags);goto done;}}if (chip->get_direction) {/* chip->get_direction may sleep */spin_unlock_irqrestore(&gpio_lock, flags);gpiod_get_direction(desc);spin_lock_irqsave(&gpio_lock, flags);}done:if (status)pr_debug("_gpio_request: gpio-%d (%s) status %d\n", desc_to_gpio(desc), label ? : "?", status);spin_unlock_irqrestore(&gpio_lock, flags);return status;}

Q&A

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一、驱动中是如何调到gpiolib.c中的gpio_reuqset函数的？

(1)头文件包含
#inlcude <linux/gpio.h>


#ifdef CONFIG_GPIOLIB

#ifdef CONFIG_ARCH_HAVE_CUSTOM_GPIO_H
#include <asm/gpio.h>
#else
#include <asm-generic/gpio.h>
#endif /* ! CONFIG_ARCH_HAVE_CUSTOM_GPIO_H */

#else /* ! CONFIG_GPIOLIB */

......

#endif /* ! CONFIG_GPIOLIB */


(2)函数声明
include/asm-generic/gpio.h
extern int gpio_request(unsigned gpio, const char *label);

(3)符号导出
drivers/gpio/gpiolib.c
EXPORT_SYMBOL_GPL(gpio_request);




二、gpio_requset的返回值

根据官方文档Documentation/gpio.txt可知返回值有如下关系

0 ：成功
负值 ：失败

具体分析gpiod_request函数
(1)
if (!desc) {
pr_warn("%s: invalid GPIO\n", __func__);
return -EINVAL;
}
(2)
if (chip == NULL)
return -EPROBE_DEFER;

(3)
if (!try_module_get(chip->owner))
return -EPROBE_DEFER;
(4)
if (test_and_set_bit(FLAG_REQUESTED, &desc->flags) == 0)
return -EBUSY;

因此，在写驱动代码时如下判错是错误的！

ret = gpio_request(RST_PORT, "GSL_RST");if (ret) { //错误的写法，判错条件应为ret < 0printk( "ret = %d : could not req gpio reset\n", ret);}

三、当gpio被其他模块占用时怎么快速定位

根据gpio序号，在注册的函数中加入log可以打印申请该gpio序号的label

int gpio_request(unsigned gpio, const char *label){<span style="color:#ff0000;">if (gpio == 128) {printk("gpio[%d] label = %s\n",label);}</span>return gpiod_request(gpio_to_desc(gpio), label);}