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>
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