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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>
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ae9847f48a
commit
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2 changed files with 32 additions and 7 deletions
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@ -2548,20 +2548,31 @@ int gpiod_direction_input(struct gpio_desc *desc)
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VALIDATE_DESC(desc);
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chip = desc->gdev->chip;
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/*
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* It is legal to have no .get() and .direction_input() specified if
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* the chip is output-only, but you can't specify .direction_input()
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* and not support the .get() operation, that doesn't make sense.
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*/
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if (!chip->get && chip->direction_input) {
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gpiod_warn(desc,
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"%s: missing get() and direction_input() operations\n",
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__func__);
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"%s: missing get() but have direction_input()\n",
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__func__);
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return -EIO;
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}
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/*
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* If we have a .direction_input() callback, things are simple,
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* just call it. Else we are some input-only chip so try to check the
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* direction (if .get_direction() is supported) else we silently
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* assume we are in input mode after this.
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*/
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if (chip->direction_input) {
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status = chip->direction_input(chip, gpio_chip_hwgpio(desc));
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} else if (chip->get_direction &&
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(chip->get_direction(chip, gpio_chip_hwgpio(desc)) != 1)) {
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gpiod_warn(desc,
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"%s: missing direction_input() operation\n",
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__func__);
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"%s: missing direction_input() operation and line is output\n",
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__func__);
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return -EIO;
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}
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if (status == 0)
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@ -2587,16 +2598,22 @@ static int gpiod_direction_output_raw_commit(struct gpio_desc *desc, int value)
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int val = !!value;
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int ret = 0;
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/*
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* It's OK not to specify .direction_output() if the gpiochip is
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* output-only, but if there is then not even a .set() operation it
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* is pretty tricky to drive the output line.
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*/
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if (!gc->set && !gc->direction_output) {
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gpiod_warn(desc,
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"%s: missing set() and direction_output() operations\n",
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__func__);
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"%s: missing set() and direction_output() operations\n",
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__func__);
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return -EIO;
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}
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if (gc->direction_output) {
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ret = gc->direction_output(gc, gpio_chip_hwgpio(desc), val);
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} else {
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/* Check that we are in output mode if we can */
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if (gc->get_direction &&
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gc->get_direction(gc, gpio_chip_hwgpio(desc))) {
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gpiod_warn(desc,
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@ -2604,6 +2621,10 @@ static int gpiod_direction_output_raw_commit(struct gpio_desc *desc, int value)
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__func__);
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return -EIO;
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}
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/*
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* If we can't actively set the direction, we are some
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* output-only chip, so just drive the output as desired.
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*/
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gc->set(gc, gpio_chip_hwgpio(desc), val);
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}
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@ -178,9 +178,13 @@ static inline struct gpio_irq_chip *to_gpio_irq_chip(struct irq_chip *chip)
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* @free: optional hook for chip-specific deactivation, such as
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* disabling module power and clock; may sleep
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* @get_direction: returns direction for signal "offset", 0=out, 1=in,
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* (same as GPIOF_DIR_XXX), or negative error
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* (same as GPIOF_DIR_XXX), or negative error.
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* It is recommended to always implement this function, even on
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* input-only or output-only gpio chips.
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* @direction_input: configures signal "offset" as input, or returns error
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* This can be omitted on input-only or output-only gpio chips.
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* @direction_output: configures signal "offset" as output, or returns error
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* This can be omitted on input-only or output-only gpio chips.
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* @get: returns value for signal "offset", 0=low, 1=high, or negative error
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* @get_multiple: reads values for multiple signals defined by "mask" and
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* stores them in "bits", returns 0 on success or negative error
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