Re: [PATCH 0/2] drm/client: Keep larger modes in connector->modes on fbdev hotplug

[Ville Syrjälä]

On Thu, Oct 15, 2026 at 10:25:43PM +0100, Hugo Sales wrote:
> On an ASUS ROG Flow X13 with a 3840x2400 eDP panel, booted with
> video=eDP-1:1920x1200@60, an HDMI hotplug makes fbdev reprobe every
> connector with its 1920x1200 framebuffer as the limit. connector->modes
> loses the panel's 3840x2400 mode, and after suspend/resume amdgpu drives
> the panel with the 1920x1200 timing. The image ends up squeezed into the
> top-left corner. Details are in
> https://gitlab.freedesktop.org/drm/amd/-/issues/5983

Sounds like an amdgpu bug.

> 
> Patch 1 makes drm_client_modeset_probe() probe with the device's limits
> and moves the framebuffer size check into the fbdev mode pickers.
> Patch 2 adds KUnit tests for it
> 
> fbdev's hotplug probe has passed the framebuffer size since 2010
> (4abe35204af8). The pickers didn't check mode sizes then, so leaving
> larger modes out of the list was what kept fbdev from picking one. They
> check the size themselves now, so the probe can use the device's limits
> like initial setup, drm_log and GETCONNECTOR already do
> 
> The HiBMC thread "[RFC] drm/client: Relax clone mode selection in
> drm_client_target_cloned" runs into the same pruning: its 640x480
> framebuffer removes 1024x768 from both connectors' lists. With this
> series userspace sees that mode again, but fbdev still can't use it, so
> this doesn't replace that RFC:
> https://lore.kernel.org/r/a48e0b33-7eab-478e-a396-b6e76b7a066f@xxxxxxxxxx
> 
> I sent an amdgpu fix for the same symptom separately. It makes amdgpu
> fall back to the encoder's native mode on eDP and LVDS:
> https://lore.kernel.org/r/20261014223041.171317-1-hugo@xxxxxxx
> This series fixes the shared mode list for every driver instead. Either
> one alone fixes the reported bug, from my testing
> 
> On amd-staging-drm-next with only this series applied, with an HDMI
> hotplug and suspend/resume (pm_test=platform) in a loop, 255 of 255
> resumes kept the native timing. Without it, 28 of 29 came back with the
> wrong timing, and the same loop on unpatched v7.2.8 got it wrong in 103
> of 103. The drm KUnit tests pass, also under KASAN, which reports
> nothing in the code this series touches
> 
> Hugo Sales (2):
>   drm/client: Probe connectors with the device's mode size limits
>   drm/tests: Add KUnit tests for the client mode size limits
> 
>  drivers/gpu/drm/drm_client_modeset.c          |  57 +++--
>  .../gpu/drm/tests/drm_client_modeset_test.c   | 222 +++++++++++++++++-
>  2 files changed, 260 insertions(+), 19 deletions(-)
> 
> -- 
> 2.55.0

-- 
Ville Syrjälä
Intel