arm平台通用gpio的相关函数说明（1）

1）说明

为了使得gpio的相关函数，具有更好的可移植性。Linux定义了一套通用的gpio结构和接口函数。如果在linux内核配置选项中，选择GENERIC_GPIO选项，就说明该平台支持通用的GPIO接口。

在Documentation/gpio.txt详细解释gpio的通用结构和相关函数。

2）头文件

在arm架构下，在以下4个地方包含了gpio.h文件。

include/linux/gpio.h

include/asm-generic/gpio.h

arch/arm/include/asm/gpio.h

arch/arm/mach-s3c2410/include/mach/gpio.h

 

这四个头文件的关系如下：

include/linux/gpio.h，包含了arch/arm/include/asm/gpio.h（需要定义CONFIG_GENERIC_GPIO）

#ifndef __LINUX_GPIO_H
#define __LINUX_GPIO_H

/* see Documentation/gpio.txt */

#ifdef CONFIG_GENERIC_GPIO
#include <asm/gpio.h>

#else

#include <linux/kernel.h>
#include <linux/types.h>
#include <linux/errno.h>

struct device;

.......
实现了一些与GENERIC_GPIO类型的gpio接口函数同样声明的空函数。
.......

#endif

#endif /* __LINUX_GPIO_H */

 

arch/arm/include/asm/gpio.h包含特定平台的gpio.h，例如包含了arch/arm/mach-realview/include/mach/gpio.h。

#ifndef _ARCH_ARM_GPIO_H
#define _ARCH_ARM_GPIO_H

/* not all ARM platforms necessarily support this API ... */
#include <mach/gpio.h>

#endif /* _ARCH_ARM_GPIO_H */

 

 

arch/arm/mach-realview/include/mach/gpio.h，通常又会包含了include/asm-generic/gpio.h。在这个文件中，需要定义一个很重要的宏：ARCH_NR_GPIOS---该平台有多少个GPIO。

/* arch/arm/mach-s3c2410/include/mach/gpio.h
 *
 * Copyright (c) 2008 Simtec Electronics
 *    http://armlinux.simtec.co.uk/
 *    Ben Dooks <[e-mail]>
 *
 * S3C2410 - GPIO lib support
 *
 * 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.
*/

#define gpio_get_value    __gpio_get_value
#define gpio_set_value    __gpio_set_value
#define gpio_cansleep    __gpio_cansleep
#define gpio_to_irq    __gpio_to_irq

/* some boards require extra gpio capacity to support external
 * devices that need GPIO.
 */

#ifdef CONFIG_CPU_S3C244X
#define ARCH_NR_GPIOS    (32 * 9 + CONFIG_S3C24XX_GPIO_EXTRA)
#else
#define ARCH_NR_GPIOS    (256 + CONFIG_S3C24XX_GPIO_EXTRA)
#endif

#include <asm-generic/gpio.h>
#include <mach/gpio-nrs.h>
#include <mach/gpio-fns.h>

#ifdef CONFIG_CPU_S3C24XX
#define S3C_GPIO_END    (S3C2410_GPIO_BANKJ + 32)
#else
#define S3C_GPIO_END    (S3C2410_GPIO_BANKH + 32)
#endif

 

include/asm-generic/gpio.h，这个文件的内容不完全列出来。该文件涉及到了一个宏：CONFIG_GPIOLIB。会对GPIO接口函数的实现产生影响。

#include <linux/kernel.h>

#include <linux/types.h>

#include <linux/errno.h>

#ifdef CONFIG_GPIOLIB
#include <linux/compiler.h>
/* Platforms may implement their GPIO interface with library code,
 * at a small performance cost for non-inlined operations and some
 * extra memory (for code and for per-GPIO table entries).
 *
 * While the GPIO programming interface defines valid GPIO numbers

 * to be in the range 0..MAX_INT, this library restricts them to the

 * smaller range 0..ARCH_NR_GPIOS-1.

 */


#ifndef ARCH_NR_GPIOS
#define ARCH_NR_GPIOS 256
#endif

static inline int gpio_is_valid(int number) ----用于判断GPIO号是否可用。
{
    /* only some non-negative numbers are valid */
    return ((unsigned)number) < ARCH_NR_GPIOS;
}

struct device;
struct seq_file;
struct module;
.......
一些函数声明，宏定义。
.......
#else /* !CONFIG_HAVE_GPIO_LIB */
static inline int gpio_is_valid(int number)
{
 /* only non-negative numbers are valid */
 return number >= 0;
}
/* platforms that don't directly support access to GPIOs through I2C, SPI,
 * or other blocking infrastructure can use these wrappers.
 */
static inline int gpio_cansleep(unsigned gpio)
{
 return 0;
}
static inline int gpio_get_value_cansleep(unsigned gpio)
{
 might_sleep();
 return gpio_get_value(gpio);
}
static inline void gpio_set_value_cansleep(unsigned gpio, int value)
{
 might_sleep();
 gpio_set_value(gpio, value);
}
#endif /* !CONFIG_HAVE_GPIO_LIB */