From: Stephen Warren <swar...@nvidia.com>
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 <swar...@nvidia.com>
---
drivers/gpio/tegra_gpio.c | 18 ++++++------------
1 file changed, 6 insertions(+), 12 deletions(-)
diff --git a/drivers/gpio/tegra_gpio.c b/drivers/gpio/tegra_gpio.c
index c0ae7719e2c9..2dfd02d62053 100644
--- a/drivers/gpio/tegra_gpio.c
+++ b/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,
--
1.9.1
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