On Mon, Sep 08, 2025 at 01:31:20PM +0200, Stephan Gerhold wrote: > There have been issues with autoboot on DB410c for years, where autoboot > gets interrupted by spurious input on the UART console. I've tried fixing > this back in 2021, but it turned out this fix was not enough. Looking into > it further, there are two separate issues to fix: > > - Spurious input with UART disconnected: The RX pin is floating in this > case, resulting in garbage or a UART break event (0x00 byte). This is > interpreted as input in the autoboot prompt. Fix this by adding > bias-pull-up for the RX pin. I've made this change upstream in Linux > 6.16 for all MSM8916/MSM8939 devices and it has already landed in U-Boot > through the recent subtree update of dts/upstream. > > - Spurious input when querying console size with UART connected: It's > unclear why this happens, but it seems to be some issue in the overly > complex implementation of 4-character packing mode in the serial_msm > driver. Fix this by switching the driver to use the more simple > single-character mode, which doesn't have this issue. > > With these patches, autoboot is finally working reliably on DragonBoard > 410c (and hopefully will remain so for the future :-)). > > Signed-off-by: Stephan Gerhold <[email protected]> > --- > Changes in v2: > - Rebase on top of U-Boot master and fix conflicts > - Drop backported upstream DT changes (already landed through recent > subtree merge of DT changes in Linux 6.16) > - Link to v1: > https://lore.kernel.org/r/[email protected]
Nice fixes and cleanup, FWIW: Acked-by: Sumit Garg <[email protected]> -Sumit > > --- > Stephan Gerhold (6): > board: dragonboard410c: Drop now unneeded bootph-all for console > Revert "serial: serial_msm: Delay initialization to let pins stabilize" > serial: msm: Cleanup register naming > serial: msm: Reset after writing to DMEN > serial: msm: Re-enable after resetting > serial: msm: Use single character mode > > arch/arm/dts/apq8016-sbc-u-boot.dtsi | 9 --- > drivers/serial/serial_msm.c | 127 > ++++++++--------------------------- > 2 files changed, 29 insertions(+), 107 deletions(-) > --- > base-commit: 328747974a0620d0996113fe2b3906b06e96de00 > change-id: 20250419-db410c-autoboot-fixes-ad7f4f5973a8 > > Best regards, > -- > Stephan Gerhold <[email protected]> >
