ARM: tegra: don't enable GPIOs until direction is set

Tegra's GPIO driver currently enables pins as GPIO as soon as they're
requested. This is not safe, since the desired direction and output value
are not yet known. This could cause a glitch on the output pins between
gpio_request() and gpio_direction_*(), depending on what values happen to
be in the GPIO controller's in/out and out-value registers vs. the final
desired configuration.

To solve this, defer enabling pins as GPIOs until some gpio_direction_*()
is invoked, and the desired configuration is explicitly programmed.

In theory this change could cause regressions, if code exists that claims
a GPIO, never explicitly sets a direction, and then gets/sets the GPIO
value based on that assumption. However, I've read through all the Tegra-
related board files and device drivers that touch GPIOs and I do not see
such buggy code anywhere.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Tom Warren <twarren@nvidia.com>

drivers/gpio/tegra_gpio.c

@@ -136,17 +136,6 @@ static void set_level(unsigned gpio, int high)
  * Generic_GPIO primitives.
  */
 
-static int tegra_gpio_request(struct udevice *dev, unsigned offset,
-			      const char *label)
-{
-	struct tegra_port_info *state = dev_get_priv(dev);
-
-	/* Configure as a GPIO */
-	set_config(state->base_gpio + offset, 1);
-
-	return 0;
-}
-
 /* set GPIO pin 'gpio' as an input */
 static int tegra_gpio_direction_input(struct udevice *dev, unsigned offset)
 {
@@ -155,6 +144,9 @@ static int tegra_gpio_direction_input(struct udevice *dev, unsigned offset)
 	/* Configure GPIO direction as input. */
 	set_direction(state->base_gpio + offset, 0);
 
+	/* Enable the pin as a GPIO */
+	set_config(state->base_gpio + offset, 1);
+
 	return 0;
 }
 
@@ -171,6 +163,9 @@ static int tegra_gpio_direction_output(struct udevice *dev, unsigned offset,
 	/* Configure GPIO direction as output. */
 	set_direction(gpio, 1);
 
+	/* Enable the pin as a GPIO */
+	set_config(state->base_gpio + offset, 1);
+
 	return 0;
 }
 
@@ -256,7 +251,6 @@ static int tegra_gpio_xlate(struct udevice *dev, struct gpio_desc *desc,
 }
 
 static const struct dm_gpio_ops gpio_tegra_ops = {
-	.request		= tegra_gpio_request,
 	.direction_input	= tegra_gpio_direction_input,
 	.direction_output	= tegra_gpio_direction_output,
 	.get_value		= tegra_gpio_get_value,