From: Stephen Warren swarren@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 swarren@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,