1、我们曾经在前面看到这个函数，源码如下：
__init void s3c_gpiolib_add(struct s3c_gpio_chip *chip){struct gpio_chip *gc = &chip->chip;int ret;BUG_ON(!chip->base);BUG_ON(!gc->label);BUG_ON(!gc->ngpio);if (!gc->direction_input)gc->direction_input = s3c_gpiolib_input;if (!gc->direction_output)gc->direction_output = s3c_gpiolib_output;if (!gc->set)gc->set = s3c_gpiolib_set;if (!gc->get)gc->get = s3c_gpiolib_get;当初只是对这一部分，说明gc内部成员的赋值，而没具体分析这几个函数，我里的几个函数并不是对每个GPIO都实用，有些我们定义了新的函数，所以并不用这些默认值，希望你能分清，那些用的是默认值，哪些是我们新定义的。我们现在分析下。/* gpiochip_add() prints own failure message on error. */ret = gpiochip_add(gc);if (ret >= 0)s3c_gpiolib_track(chip);
}
2、这几个函数的源码都在linux/arch/arm/plat-s3c/gpio.c文件中：
/* Default routines for controlling GPIO, based on the original S3C24XX* GPIO functions which deal with the case where each gpio bank of the* chip is as following:** base + 0x00: Control register, 2 bits per gpio* gpio n: 2 bits starting at (2*n)*00 = input, 01 = output, others mean special-function
以前是4位，现在是2位，区别就在这里* base + 0x04: Data register, 1 bit per gpio*bit n: data bit n*/static int s3c_gpiolib_input(struct gpio_chip *chip, unsigned offset){struct s3c_gpio_chip *ourchip = to_s3c_gpio(chip);void __iomem *base = ourchip->base; 这些都和前面一样unsigned long flags;unsigned long con;local_irq_save(flags);con = __raw_readl(base + 0x00);con &= ~(3 << (offset * 2));__raw_writel(con, base + 0x00);local_irq_restore(flags);return 0;}
static int s3c_gpiolib_output(struct gpio_chip *chip, unsigned offset, int value){struct s3c_gpio_chip *ourchip = to_s3c_gpio(chip);void __iomem *base = ourchip->base;unsigned long flags;unsigned long dat;unsigned long con;local_irq_save(flags);dat = __raw_readl(base + 0x04);dat &= ~(1 << offset);if (value)dat |= 1 << offset;__raw_writel(dat, base + 0x04);con = __raw_readl(base + 0x00);con &= ~(3 << (offset * 2));con |= 1 << (offset * 2);__raw_writel(con, base + 0x00);__raw_writel(dat, base + 0x04);
__raw_writel(dat, base + OFF_GPDAT);写数据寄存器__raw_writel(con, base + OFF_GPCON);写控制寄存器__raw_writel(dat, base + OFF_GPDAT);写数据寄存器
这里有个疑问，为何要写两次数据寄存器？
local_irq_restore(flags);return 0;}
这两个函数是针对数据寄存器的，所以对4位，2位的控制寄存器都实用，因为数据寄存器中1位表示一个IO口，大家都一样，所以没必要特殊化。当然，使用的场合就有所不同，我想一般在设置为输出的时候才需要对某一位设置成1或者0吧？在设置为输入的时候，才需要读取吧？函数很简单，就不分析了。static void s3c_gpiolib_set(struct gpio_chip *chip, unsigned offset, int value){struct s3c_gpio_chip *ourchip = to_s3c_gpio(chip);void __iomem *base = ourchip->base;unsigned long flags;unsigned long dat;local_irq_save(flags);dat = __raw_readl(base + 0x04);dat &= ~(1 << offset);if (value)dat |= 1 << offset;__raw_writel(dat, base + 0x04);local_irq_restore(flags);}
static int s3c_gpiolib_get(struct gpio_chip *chip, unsigned offset){struct s3c_gpio_chip *ourchip = to_s3c_gpio(chip);unsigned long val;val = __raw_readl(ourchip->base + 0x04);val >>= offset;val &= 1;return val;}
别人失去了信心，他却下决心实现自己的目标。
