struct of_phandle_args
#define MAX_PHANDLE_ARGS 16
struct of_phandle_args {
struct device_node *np;
int args_count;
uint32_t args[MAX_PHANDLE_ARGS];
};
1 gpiod_get()
/*
* 1. 函数适用于只有一个gpio，index为0，即list = <&phandle1 1 2>;
* 2. 如果想使用phandle2，list = <&phandle1 1 2 &phandle2 3 3>;
* 则为 gpiod_get_index(dev, con_id, 1, flags);
*/
struct gpio_desc *__must_check gpiod_get(struct device *dev, const char *con_id,
enum gpiod_flags flags)
{
return gpiod_get_index(dev, con_id, 0, flags);
}
struct gpio_desc *__must_check gpiod_get_index(struct device *dev,
const char *con_id,
unsigned int idx,
enum gpiod_flags flags)
{
struct gpio_desc *desc = NULL;
int status;
enum gpio_lookup_flags lookupflags = 0;
if (dev) {
/*使用dt*/
if (IS_ENABLED(CONFIG_OF) && dev->of_node) {
/*
* 解析dt,找到gpio-controller，根据解析的引脚号，
* 找到对应 gpio-controller 的 gpio_desc。
*/
desc = of_find_gpio(dev, con_id, idx, &lookupflags);
}
}
/* 有关"gpio-ranges",没什么用 */
status = gpiod_request(desc, con_id);
/* 根据传入flag设置方向，flag为null会设为输入 */
status = gpiod_configure_flags(desc, con_id, lookupflags, flags);
return desc;
}
1-1 of_find_gpio()
static const char * const gpio_suffixes[] = { "gpios", "gpio" };
struct gpio_desc *of_find_gpio(struct device *dev, const char *con_id,
unsigned int idx,
enum gpio_lookup_flags *flags)
{
char prop_name[32]; /* 32 is max size of property name */
enum of_gpio_flags of_flags;
struct gpio_desc *desc;
unsigned int i;
for (i = 0; i < ARRAY_SIZE(gpio_suffixes); i++) {
/* 如 "led-gpios" 或 "led-gpio" 的属性名 */
if (con_id)
snprintf(prop_name, sizeof(prop_name), "%s-%s", con_id,
gpio_suffixes[i]);
/* 合成，如 "gpios" 或 "gpio" 的属性名 */
else
snprintf(prop_name, sizeof(prop_name), "%s",
gpio_suffixes[i]);
/*
* 1. 根据属性名(led-gpios)查找匹配，保存内容在gpio_desc
* 2. 根据gpiospec的phandle找到chip，即：有gpio-controller的节点。
* 3. 根据gpiospec的引脚号，找到在chip中的desc数组偏移位置，
* 即对应的引脚号的desc
* 4. 并返回了flags "OF_GPIO_ACTIVE_LOW"
*/
desc = of_get_named_gpiod_flags(dev->of_node, prop_name, idx,
&of_flags);
}
/* 如果是低电平有效，设置flag */
if (of_flags & OF_GPIO_ACTIVE_LOW)
*flags |= GPIO_ACTIVE_LOW;
if (of_flags & OF_GPIO_SINGLE_ENDED) {
if (of_flags & OF_GPIO_ACTIVE_LOW)
*flags |= GPIO_OPEN_DRAIN;
else
*flags |= GPIO_OPEN_SOURCE;
}
return desc;
}
1-1-1 of_get_named_gpiod_flags()
/*
* 1. 在user的node(如led)，解析dt有关gpio的内容，
* 2. 寻找要调用的gpio-controller，进而找到gpiochip
* 3. 通过dt提供的引脚号，找到对应引脚的gpio_desc
*/
struct gpio_desc *of_get_named_gpiod_flags(struct device_node *np,
const char *propname, int index, enum of_gpio_flags *flags)
{
struct of_phandle_args gpiospec;
struct gpio_chip *chip;
struct gpio_desc *desc;
int ret;
/*
* propname：当前node的属性名
* "#gpio-cells"：父node的属性名
* index：第index个phandle
* 举例：propname = <&phandle1 1 2 &phandle2 3>;
* 1. 当#gpio-cells为2，index为0时，
* 2. gpiospec->arg[0] = 1 | [1] = 2;
* gpiospec->args_count = 2;
* gpiospec->np = phandle1;
*/
ret = of_parse_phandle_with_args(np, propname, "#gpio-cells", index,
&gpiospec);
/* 根据gpiospec，遍历 gpio_devices，找到匹配的gpiochip */
chip = of_find_gpiochip_by_xlate(&gpiospec);
/* 根据dt中，"xx-gpios"属性提供的引脚号，找到对应引脚的gpio_desc */
desc = of_xlate_and_get_gpiod_flags(chip, &gpiospec, flags);
return desc;
}
1-2 gpiod_request()
/*
* desc：对应引脚号的gpio_desc
* lable："led"
*/
int gpiod_request(struct gpio_desc *desc, const char *label)
{
int status = -EPROBE_DEFER;
struct gpio_device *gdev;
gdev = desc->gdev;
status = __gpiod_request(desc, label);
return status;
}
static int __gpiod_request(struct gpio_desc *desc, const char *label)
{
struct gpio_chip *chip = desc->gdev->chip;
int status;
unsigned long flags;
/* 设置label("led-gpios的led").如果为NULL,设置为"?" */
desc_set_label(desc, label ? : "?");
status = 0;
/* 没有"gpio-ranges"属性，无作用 */
if (chip->request) {
/* mxc_gpio_request */
status = chip->request(chip, gpio_chip_hwgpio(desc));
}
/*获得gpio方向*/
if (chip->get_direction) {
gpiod_get_direction(desc);
}
return status;
}
1-3 gpiod_configure_flags()
/**
* gpiod_configure_flags - helper function to configure a given GPIO
* @desc: gpio whose value will be assigned
* @con_id: function within the GPIO consumer
* @lflags: gpio_lookup_flags - returned from of_find_gpio() or
* of_get_gpio_hog()
* @dflags: gpiod_flags - optional GPIO initialization flags
*
* Return 0 on success, -ENOENT if no GPIO has been assigned to the
* requested function and/or index, or another IS_ERR() code if an error
* occurred while trying to acquire the GPIO.
*/
static int gpiod_configure_flags(struct gpio_desc *desc, const char *con_id,
unsigned long lflags, enum gpiod_flags dflags)
{
int status;
/*
* 将解析dt的flag，记录在对应引脚的gpio_desc->flags
* 用途是实现逻辑电平的统一，无关实际物理电平。
*/
if (lflags & GPIO_ACTIVE_LOW)
set_bit(FLAG_ACTIVE_LOW, &desc->flags);
if (lflags & GPIO_OPEN_DRAIN)
set_bit(FLAG_OPEN_DRAIN, &desc->flags);
if (lflags & GPIO_OPEN_SOURCE)
set_bit(FLAG_OPEN_SOURCE, &desc->flags);
/*
* gpio_get解析传入的flag，引脚设置方向
* GPIOD_FLAGS_BIT_DIR_OUT： 输出
* others： 输入
*/
if (dflags & GPIOD_FLAGS_BIT_DIR_OUT)
status = gpiod_direction_output(desc,
dflags & GPIOD_FLAGS_BIT_DIR_VAL);
else
status = gpiod_direction_input(desc);
return status;
}
总结
-
gpiod_get_index（index）
- 根据传入参数index，确认要使用“xxx-gpios”的第几个pin。
- 解析dt属性，获取使用了哪个gpio-controller，使用了哪个引脚号。
- 找到gpio-controller节点，获取已配置好的gpio_device。
- 根据引脚号，找到对应挂在gpio_device的gpio_desc，返回给user。
-
gpiod_set_value()，gpiod_direction_output()，gpiod_direction_input() 等
-
因为已经获得gpio_desc，则反向找到gpio_device的gpiochip。
-
利用gpiochip提供的中间层函数，操作gpio，如设置电平，设置方向。
-
-
在dt中，”ngpios”为gpio寄存器的可使用的数量，即寄存器是32位宽，但只有18位对应了控制引脚，1个gpio-controller控制18个pin，设置"ngpios = <18>，通知driver只有18个pin。