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

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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>
This commit is contained in:
Stephen Warren 2015-09-23 12:13:00 -06:00 committed by Tom Warren
parent f9d3cab091
commit 0c35e3a8b4
1 changed files with 6 additions and 12 deletions
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18
drivers/gpio/tegra_gpio.c
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@ -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,