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author | Linus Walleij <linus.walleij@linaro.org> | 2018-09-25 09:54:14 +0200 |
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committer | Linus Walleij <linus.walleij@linaro.org> | 2018-09-25 09:54:14 +0200 |
commit | e48d194d1204b19655c1a9d78a67f2f01d2fe432 (patch) | |
tree | 13655545f5f1c22547a171b23c56eb98ded6a09b /drivers/gpio | |
parent | ae9847f48a4b4bff0335da20be63ac84d94eb54c (diff) | |
download | linux-stable-e48d194d1204b19655c1a9d78a67f2f01d2fe432.tar.gz linux-stable-e48d194d1204b19655c1a9d78a67f2f01d2fe432.tar.bz2 linux-stable-e48d194d1204b19655c1a9d78a67f2f01d2fe432.zip |
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: Linus Walleij <linus.walleij@linaro.org>
Diffstat (limited to 'drivers/gpio')
-rw-r--r-- | drivers/gpio/gpiolib.c | 33 |
1 files changed, 27 insertions, 6 deletions
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); } |