Commit 72d32000 authored by Linus Walleij's avatar Linus Walleij
Browse files

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: default avatarLinus Walleij <linus.walleij@linaro.org>
parent e9f4d569

drivers/gpio/gpiolib.c

+24 −7
Original line number Diff line number Diff line
@@ -565,14 +565,31 @@ int gpiochip_add_data(struct gpio_chip *chip, void *data) 
		struct gpio_desc *desc = &gdev->descs[i];



		desc->gdev = gdev;

		/*

		 * REVISIT: most hardware initializes GPIOs as inputs

		 * (often with pullups enabled) so power usage is

		 * minimized. Linux code should set the gpio direction

		 * first thing; but until it does, and in case

		 * chip->get_direction is not set, we may expose the

		 * wrong direction in sysfs.

		 */



		if (chip->get_direction) {

			/*

			 * If we have .get_direction, set up the initial

			 * direction flag from the hardware.

			 */

			int dir = chip->get_direction(chip, i);



		/* REVISIT: most hardware initializes GPIOs as inputs (often

		 * with pullups enabled) so power usage is minimized. Linux

		 * code should set the gpio direction first thing; but until

		 * it does, and in case chip->get_direction is not set, we may

		 * expose the wrong direction in sysfs.

			if (!dir)

				set_bit(FLAG_IS_OUT, &desc->flags);

		} else if (!chip->direction_input) {

			/*

			 * If the chip lacks the .direction_input callback

			 * we logically assume all lines are outputs.

			 */

		desc->flags = !chip->direction_input ? (1 << FLAG_IS_OUT) : 0;

			set_bit(FLAG_IS_OUT, &desc->flags);

		}

	}



	spin_unlock_irqrestore(&gpio_lock, flags);