On Wednesday, 23 September 2015, Stephen Warren <swar...@wwwdotorg.org> wrote: > > 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(-) >
Reviewed-by: Simon Glass <s...@chromium.org> > > _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
