NACK Re: [SRU][N:OEM-6.17][PATCH 0/1] Fix i915 DP MST FEC support check for uncompressed streams

[Timo Aaltonen]

ChunAn Wu kirjoitti 20.5.2026 klo 12.52:
> BugLink: https://bugs.launchpad.net/bugs/2150523
> BugLink: https://bugs.launchpad.net/bugs/2150524
> 
> SRU Justification:
> 
> [ Impact ]
> On systems with hybrid graphics (Intel iGPU + NVIDIA dGPU), including
> Lenovo T1g/P16s and Dell Pro Max 14/16 Premium, the i915 driver
> incorrectly enables FEC for uncompressed streams on MST links when DSC
> compression is enabled for another stream on the same link. The
> downstream branch device rejects the invalid FEC configuration, causing
> the DP MST display pipeline to stall. This blocks NVIDIA modeset from
> completing its display operations, resulting in continuous timeout
> errors (nvidia-modeset: ERROR: GPU:0: Error while waiting for GPU
> progress) and preventing the NVIDIA GPU from going idle. When suspend
> is triggered, the NVIDIA driver cannot suspend the GPU due to the
> stuck channel, causing the system to fail to enter suspend or hang
> entirely.
> 
> [ Fix ]
> Cherry-pick upstream commit:
> - 06a691f0e7d0 ("drm/i915/dp_mst: Fix check for FEC support for an
>    uncompressed stream")
> 
> The fix adds a `dsc` condition check so the FEC support verification
> is only performed for compressed (DSC) streams, not for uncompressed
> streams that happen to have FEC enabled due to another stream on the
> same MST link.
> 
> [ Test Plan ]
> 1. Boot affected system (Lenovo T1g/P16s or Dell Pro Max 14/16
>     Premium) with oem-6.17 kernel (no external displays needed)
> 2. Use the system under normal workload
> 3. Trigger suspend: systemctl suspend
> 4. Verify system enters suspend successfully
> 5. Resume and check dmesg for absence of nvidia-modeset timeout errors
> 6. Repeat suspend/resume cycles to confirm stability
> 
> [ Where problems could occur ]
> The change only affects the FEC support check path for uncompressed
> streams on MST links. Risk is low as it relaxes an overly strict
> check that was already validated for the compressed stream case.
> 
> Imre Deak (1):
>    drm/i915/dp_mst: Fix check for FEC support for an uncompressed stream
> 
>   drivers/gpu/drm/i915/display/intel_dp_mst.c | 9 ++++++++-
>   1 file changed, 8 insertions(+), 1 deletion(-)
> 

as discussed elsewhere, use forgejo


-- 
Timo Aaltonen
Kernel Team
Canonical Ltd.