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 <[email protected]> > > > > 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/[email protected]/T/ Thanks, Stephan
