From e48d194d1204b19655c1a9d78a67f2f01d2fe432 Mon Sep 17 00:00:00 2001 From: Linus Walleij Date: Tue, 25 Sep 2018 09:54:14 +0200 Subject: 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 Cc: Bartosz Golaszewski Signed-off-by: Linus Walleij --- drivers/gpio/gpiolib.c | 33 +++++++++++++++++++++++++++------ 1 file changed, 27 insertions(+), 6 deletions(-) (limited to 'drivers/gpio/gpiolib.c') diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c index cabe1b460458..4ce402f9fc69 100644 --- a/drivers/gpio/gpiolib.c +++ b/drivers/gpio/gpiolib.c @@ -2548,20 +2548,31 @@ 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", - __func__); + "%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", - __func__); + "%s: missing direction_input() operation and line is output\n", + __func__); return -EIO; } if (status == 0) @@ -2587,16 +2598,22 @@ 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", - __func__); + "%s: missing set() and direction_output() operations\n", + __func__); return -EIO; } 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); } -- cgit v1.2.3