linux-kernel - Re: [PATCH 2/2] drm/msm/dpu: try reserving the DSPP-less LM first

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Message-ID: <33424a9d-10a6-4479-bba6-12f8ce60da1a@packett.cool>
Date: Tue, 27 Jan 2026 06:43:32 -0300
From: Val Packett <val@...kett.cool>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
 Rob Clark <robin.clark@....qualcomm.com>,
 Abhinav Kumar <abhinav.kumar@...ux.dev>,
 Jessica Zhang <jesszhan0024@...il.com>, Sean Paul <sean@...rly.run>,
 Marijn Suijten <marijn.suijten@...ainline.org>,
 David Airlie <airlied@...il.com>
Cc: linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] drm/msm/dpu: try reserving the DSPP-less LM first

Hi,

On 1/15/26 5:05 PM, Dmitry Baryshkov wrote:
> On most of the platforms only some mixers have connected DSPP blocks.
> If DSPP is not required for the CRTC, try looking for the LM with no
> DSSP block, leaving DSPP-enabled LMs to CRTCs which actually require
> those.
>
> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
> ---
>   drivers/gpu/drm/msm/disp/dpu1/dpu_rm.c | 52 +++++++++++++++++++++++++---------
>   1 file changed, 38 insertions(+), 14 deletions(-)


this has massively broken things on my x1e device (latitude-7455):

- upon booting into gdm, the internal display is all dark blue
- suspend-resume makes gdm appear fine, then logging in results in 
another blue screen, again bypassed by suspend-resume (vt switching back 
to gdm makes it appear fine but switching back to the session, it's 
still blue)
- OR blindly logging in on the blue gdm makes the session appear
- plugging in an external display makes the blue screen flash constantly 
over the contents, there is also a flashing vertical gap between 2 
halves of the internal screen (amazing effect) and the external display 
doesn't actually refresh the contents under the blue 
(https://owo.packett.cool/dbg/dspp-lm-boom.webm)

Consistently across 3 reboots.

Reverted only this commit and it's back to normal, so I'm pretty sure 
it's this.

/sys/kernel/debug/dri..: https://owo.packett.cool/dbg/bluewtf.dri


~val