@@ -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);
}
@@ -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
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> --- drivers/gpio/gpiolib.c | 33 +++++++++++++++++++++++++++------ include/linux/gpio/driver.h | 6 +++++- 2 files changed, 32 insertions(+), 7 deletions(-) -- 2.17.1