On Wed, Jul 14, 2021 at 10:56:26AM +0200, Stephan Gerhold wrote:
For some reason, the DragonBoard 410c aborts autoboot immediately if U-Boot is started without LK. It looks like it picks up a single broken character via serial and therefore believes a key was pressed to abort autoboot.
After some debugging, it seems like adding some delay after pinctrl setup but before UART initialization fixes the issue. It's also worth mentioning that unlike when booting from LK, the pinctrl setup is actually necessary when booting U-Boot without LK since UART is broken if the pinctrl line is removed.
I suspect that reconfiguring the pins might take some time to stabilize and if the UART controller is enabled too quickly it will pick up some random noise. Adding a few milliseconds of delay fixes the issue and shouldn't have any other negative side effects.
3ms seems to be the minimum delay required in my tests, use 5ms instead just to be sure.
Signed-off-by: Stephan Gerhold stephan@gerhold.net
Applied to u-boot/master, thanks!