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gpio: set up initial state from .get_direction()
If the gpiochip supports the .get_direction() callback, then the initial state of the descriptor flags should be set up as output accordingly. Also put in comments explaining what is going on. Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
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1 changed files with 24 additions and 7 deletions
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@ -565,14 +565,31 @@ int gpiochip_add_data(struct gpio_chip *chip, void *data)
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struct gpio_desc *desc = &gdev->descs[i];
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struct gpio_desc *desc = &gdev->descs[i];
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desc->gdev = gdev;
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desc->gdev = gdev;
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/*
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/* REVISIT: most hardware initializes GPIOs as inputs (often
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* REVISIT: most hardware initializes GPIOs as inputs
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* with pullups enabled) so power usage is minimized. Linux
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* (often with pullups enabled) so power usage is
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* code should set the gpio direction first thing; but until
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* minimized. Linux code should set the gpio direction
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* it does, and in case chip->get_direction is not set, we may
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* first thing; but until it does, and in case
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* expose the wrong direction in sysfs.
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* chip->get_direction is not set, we may expose the
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* wrong direction in sysfs.
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*/
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*/
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desc->flags = !chip->direction_input ? (1 << FLAG_IS_OUT) : 0;
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if (chip->get_direction) {
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/*
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* If we have .get_direction, set up the initial
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* direction flag from the hardware.
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*/
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int dir = chip->get_direction(chip, i);
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if (!dir)
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set_bit(FLAG_IS_OUT, &desc->flags);
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} else if (!chip->direction_input) {
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/*
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* If the chip lacks the .direction_input callback
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* we logically assume all lines are outputs.
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*/
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set_bit(FLAG_IS_OUT, &desc->flags);
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}
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}
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}
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spin_unlock_irqrestore(&gpio_lock, flags);
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spin_unlock_irqrestore(&gpio_lock, flags);
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