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>

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index bb3195d..340b021 100644 (file)
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -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.
+               /*
+                * 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.
                 */
-               desc->flags = !chip->direction_input ? (1 << FLAG_IS_OUT) : 0;
+
+               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);
+
+                       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.
+                        */
+                       set_bit(FLAG_IS_OUT, &desc->flags);
+               }
        }
 
        spin_unlock_irqrestore(&gpio_lock, flags);