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Bug#1141866: [7.1] drm/amd/display: Add dp_skip_rbr flag for NUTMEG

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On Sat, 11 Jul 2026 14:35:30 -0500 Lionso Alejandro Pacheco Vacacela
<lionso@murena.io> wrote:
[...]
> Since the 7.1.x kernels, systems with AMD CIK/GCN1.1 APUs (Kaveri,
> Kabini, Mullins) that use the analog VGA output get no display signal
> at all: the monitor enters power save at KMS takeover and never wakes.
> The machine is otherwise healthy (reachable over SSH). 7.0.x kernels
> are fine.
[...]
> Root cause (upstream): Linux 7.1 switched CIK APUs to the amdgpu DC
> display stack by default (c81f35cdbab2 "drm/amdgpu: Use DC by default
> on CIK APUs"). DC's support for the NUTMEG bridge requires forcing the
> DP link rate to HBR, but upstream commit
> 
>   a62346043a89 ("drm/amd/display: Fix coding style issue")
> 
> inadvertently broke that quirk (the preferred link rate is no longer
> applied to the link setting the algorithm iterates from), so DP link
> training against the bridge fails at RBR and the output stays dark:
> 
>   [drm] enabling link 2 failed: 15   (DC_FAIL_DP_LINK_TRAINING)
> 
> Upstream fix: "drm/amd/display: Fix preferred link rate for NUTMEG" by
> Timur Kristóf,
>
https://lore.kernel.org/amd-gfx/20260529090909.13206-1-timur.kristof@gmail.com/
> Reviewed-by: Fangzhi Zuo, applied to the amdgpu maintainer tree on
> 2026-07-10; not yet in mainline or 7.1.y at the time of writing. Also
> tracked as https://gitlab.freedesktop.org/drm/amd/-/issues/5465.
[...]

This ended up as commit 9fb646bc4d87f62bcbf0a7ea326430eb802c475c in
7.2-rc4.  Please queue it up for 7.1-stable.

Ben.

-- 
Ben Hutchings
Experience is what causes a person to make new mistakes
instead of old ones.

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Bug#1141866: linux-image-7.1.3+deb14-amd64: no display on AMD Kaveri/CIK APU VGA output (amdgpu DC regression) Lionso Alejandro Pacheco Vacacela <lionso@murena.io> - 2026-07-11 21:50 +0200
  Bug#1141866: [7.1] drm/amd/display: Add dp_skip_rbr flag for NUTMEG Ben Hutchings <ben@decadent.org.uk> - 2026-07-26 16:10 +0200
    Bug#1141866: [7.1] drm/amd/display: Add dp_skip_rbr flag for NUTMEG Sasha Levin <sashal@kernel.org> - 2026-07-28 00:30 +0200

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