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

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Message-ID: <whko2yur7tgutr4qhlbqfrvpcdg7hkyw66koicqvpvfhk55c7z@saj2uxrduv4z>
Date: Tue, 27 Jan 2026 12:34:33 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Val Packett <val@...kett.cool>
Cc: 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>, 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

On Tue, Jan 27, 2026 at 06:43:32AM -0300, Val Packett wrote:
> 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.

Interesting. Could you please capture the dri-state (only the last part,
resource mapping) with the external monitor attached and with this
commit reverted?

Also, could you please run another check:
 - revert this commit
 - comment out LM_2, LM_3 in the catalog
 - try the resulting kernel with the external monitor

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

-- 
With best wishes
Dmitry