rockchip-drm display-subsystem: [drm] *ERROR* POST_BUF_EMPTY irq err at vp0

[Cristian Ciocaltea]

On 3/13/25 4:13 PM, Marcin Juszkiewicz wrote:
> I took my FriendlyELEC NanoPC-T6 LTS back to operation. Installed Fedora
> rawhide on it and trying to get screen working.
> 
> Running 6.14-rc6 on it. Kernel log is full of this message:
> 
> rockchip-drm display-subsystem: [drm] *ERROR* POST_BUF_EMPTY irq err at vp0
> 
> /sys/devices/platform/display-subsystem/drm/card0/card0-HDMI-A-1/modes
> shows list of resolutions available on my 10" screen. Monitor says
> "HDMI: no signal".
> 
> I remember having screen running once with some set of out-of-tree
> patches but iirc it was before HDMI0 support was present in mainline.
> 
> Where I should look?

I need access to the full kernel log, but before that do the following:

1. Ensure the kernel is built with dynamic debug support

  CONFIG_DYNAMIC_DEBUG=y

2. Append the following to kernel cmdline:

  rockchipdrm.dyndbg=+p dw_hdmi_qp.dyndbg=+p phy_rockchip_samsung_hdptx.dyndbg=+p

3. Deploy the updated kernel (if needed) and reboot 
4. Unplug the screen from the HDMI port

5. Open a console terminal (SSH or serial) and run:

  echo 0x4 > /sys/module/drm/parameters/debug

6. Plug the screen back
7. Wait a few seconds
8. Get the kernel log