Hi, during the investigations of the recent VC4 HDMI Sink issue [1], I was able to reproduce another issue with vc4 after s2idle resume. Sometimes ( probability ~ 1 : 30 cases ) I'm able to trigger a HVS underrun and it's impact is that the HDMI display stays black and unusable: [ 1790.139465] PM: suspend exit [ 1790.153998] lan78xx 1-1.1.1:1.0 eth0: Link is Down [ 1790.548866] vc4-drm soc:gpu: [drm:vc4_hvs_irq_handler [vc4]] *ERROR* HVS underrun [ 1794.713952] net_ratelimit: 2 callbacks suppressed So I need to use the Debug UART after that. Scenario: Steps: 1. Flash latest Raspberry Pi OS (32 bit) on SD card 2. Build Kernel from repo [2] which based on Linux 6.12-rc3 above with arm/multi_v7_defconfig 3. Replace Kernel, modules + DTB on SD card with build ones 4. add the following to confix.txt device_tree=bcm2837-rpi-3-b-plus.dtb enable_uart=1 5. change/add the following to cmdline.txt console=ttyS1,11520 no_console_suspend=1 6. connect the following devices to Raspberry Pi 3 B+ : USB mouse USB keyboard Logilink HDMI switch + HDMI monitor Debug UART adapter (USB side to PC) 7. Power on board and boot into X11 8. Change to root 9. Enable wakeup for ttyS1 ( echo enabled > /sys/class/tty/ttyS1/power/wakeup ) 10. Trigger suspend to idle via X11 (echo freeze > /sys/power/state) 11. Wakeup Raspberry Pi via Debug UART Currently I don't see a relation to the VC4 HDMI Sink issue, because this issue occur independently. Until now i wasn't able to reproduce it without the HDMI Switch. Not sure this is related but sometimes the cursor is also corrupted with noise after resume. What can I do to investigate this further? [1] - https://lore.kernel.org/dri-devel/c657d3e9-e4fb-4dac-a611-45655511e500@xxxxxxx/ [2] - https://github.com/lategoodbye/linux-dev/commits/v6.12-pm_v2/
