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Commit e48d194d authored by Linus Walleij's avatar Linus Walleij
Browse files

gpio: Add comments on single direction chips 



A patch from Ricardo got me thinking about some gpio chip
semantics so let's drop in some comments to make things
more clear around that.

Cc: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Cc: Bartosz Golaszewski <brgl@bgdev.pl>
Signed-off-by: default avatarLinus Walleij <linus.walleij@linaro.org>
parent ae9847f4

drivers/gpio/gpiolib.c

+27 −6
Original line number Diff line number Diff line
@@ -2548,19 +2548,30 @@ int gpiod_direction_input(struct gpio_desc *desc) 
	VALIDATE_DESC(desc);

	chip = desc->gdev->chip;



	/*

	 * It is legal to have no .get() and .direction_input() specified if

	 * the chip is output-only, but you can't specify .direction_input()

	 * and not support the .get() operation, that doesn't make sense.

	 */

	if (!chip->get && chip->direction_input) {

		gpiod_warn(desc,

			"%s: missing get() and direction_input() operations\n",

			   "%s: missing get() but have direction_input()\n",

			   __func__);

		return -EIO;

	}



	/*

	 * If we have a .direction_input() callback, things are simple,

	 * just call it. Else we are some input-only chip so try to check the

	 * direction (if .get_direction() is supported) else we silently

	 * assume we are in input mode after this.

	 */

	if (chip->direction_input) {

		status = chip->direction_input(chip, gpio_chip_hwgpio(desc));

	} else if (chip->get_direction &&

		  (chip->get_direction(chip, gpio_chip_hwgpio(desc)) != 1)) {

		gpiod_warn(desc,

			"%s: missing direction_input() operation\n",

			   "%s: missing direction_input() operation and line is output\n",

			   __func__);

		return -EIO;

	}
@@ -2587,6 +2598,11 @@ static int gpiod_direction_output_raw_commit(struct gpio_desc *desc, int value) 
	int val = !!value;

	int ret = 0;



	/*

	 * It's OK not to specify .direction_output() if the gpiochip is

	 * output-only, but if there is then not even a .set() operation it

	 * is pretty tricky to drive the output line.

	 */

	if (!gc->set && !gc->direction_output) {

		gpiod_warn(desc,

			   "%s: missing set() and direction_output() operations\n",
@@ -2597,6 +2613,7 @@ static int gpiod_direction_output_raw_commit(struct gpio_desc *desc, int value) 
	if (gc->direction_output) {

		ret = gc->direction_output(gc, gpio_chip_hwgpio(desc), val);

	} else {

		/* Check that we are in output mode if we can */

		if (gc->get_direction &&

		    gc->get_direction(gc, gpio_chip_hwgpio(desc))) {

			gpiod_warn(desc,
@@ -2604,6 +2621,10 @@ static int gpiod_direction_output_raw_commit(struct gpio_desc *desc, int value) 
				__func__);

			return -EIO;

		}

		/*

		 * If we can't actively set the direction, we are some

		 * output-only chip, so just drive the output as desired.

		 */

		gc->set(gc, gpio_chip_hwgpio(desc), val);

	}

include/linux/gpio/driver.h

+5 −1
Original line number Diff line number Diff line
@@ -178,9 +178,13 @@ static inline struct gpio_irq_chip *to_gpio_irq_chip(struct irq_chip *chip) 
 * @free: optional hook for chip-specific deactivation, such as

 *	disabling module power and clock; may sleep

 * @get_direction: returns direction for signal "offset", 0=out, 1=in,

 *	(same as GPIOF_DIR_XXX), or negative error

 *	(same as GPIOF_DIR_XXX), or negative error.

 *	It is recommended to always implement this function, even on

 *	input-only or output-only gpio chips.

 * @direction_input: configures signal "offset" as input, or returns error

 *	This can be omitted on input-only or output-only gpio chips.

 * @direction_output: configures signal "offset" as output, or returns error

 *	This can be omitted on input-only or output-only gpio chips.

 * @get: returns value for signal "offset", 0=low, 1=high, or negative error

 * @get_multiple: reads values for multiple signals defined by "mask" and

 *	stores them in "bits", returns 0 on success or negative error