[PATCH 3/3] serial: serial_msm: Delay initialization to let pins stabilize

[Tom Rini]

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 at gerhold.net>

Applied to u-boot/master, thanks!

-- 
Tom
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