Re: [PATCH] qcom_defconfig: Enable AUTOBOOT_KEYED support

[Stephan Gerhold <stephan.gerhold@linaro.org>]

On Fri, May 09, 2025 at 12:45:20PM +0200, Casey Connolly wrote:
> On 5/8/25 12:32, Sumit Garg wrote:
> > From: Sumit Garg <sumit.garg@oss.qualcomm.com>
> > 
> > When debug serial port isn't connected, it is at least reported on RB1
> > that autoboot gets interrupted. It is probably due to random characters
> > on the UART RX line when disconnected. Lets try to fix this inconsistent
> > behaviour via enabling AUTOBOOT_KEYED such that the autoboot gets
> > interrupted only when the <SPACE> key gets pressed.
> 
> Honestly I'd much rather fix the bug in the UART driver, maybe it's broken
> pinctrl?
> 
> The older UART driver (for msm8916) had a similar but that Stephen was able
> to fix with better configuration.
> 
> Anyhow, this is a sensible enough workaround if nobody wants to look into
> GENI...
> 

Well, the main fix I did for that isn't related to the UART driver at
all, it's simply adding bias-pull-up for the RX pin so that it isn't
left floating when UART is not connected.

For RB1, qcm2290.dtsi &qup_uart4_default currently has bias-disable for
both RX and TX pins. So please try applying bias-pull-up + bootph-all
for the GPIO that belongs to RX.

For details, please see the following patch series for MSM8916:
https://lore.kernel.org/linux-arm-msm/20250422-msm8916-console-pinctrl-v2-0-f345b7a53c91@linaro.org/T/

Thanks,
Stephan