linux-kernel - Re: drm/msm: DisplayPort regressions in 6.8-rc1

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Message-ID: <ZdDPISS5ntrWSPf_@hovoldconsulting.com>
Date: Sat, 17 Feb 2024 16:22:09 +0100
From: Johan Hovold <johan@...nel.org>
To: Rob Clark <robdclark@...il.com>,
	Abhinav Kumar <quic_abhinavk@...cinc.com>,
	Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
	Kuogee Hsieh <quic_khsieh@...cinc.com>
Cc: Sean Paul <sean@...rly.run>,
	Marijn Suijten <marijn.suijten@...ainline.org>,
	David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
	Bjorn Andersson <quic_bjorande@...cinc.com>,
	quic_jesszhan@...cinc.com, quic_sbillaka@...cinc.com,
	dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
	linux-arm-msm@...r.kernel.org, regressions@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: drm/msm: DisplayPort regressions in 6.8-rc1

On Tue, Feb 13, 2024 at 12:42:17PM +0100, Johan Hovold wrote:

> Since 6.8-rc1 the internal eDP display on the Lenovo ThinkPad X13s does
> not always show up on boot.
> 
> The logs indicate problems with the runtime PM and eDP rework that went
> into 6.8-rc1:
> 
> 	[    6.007872] [drm:drm_bridge_attach [drm]] *ERROR* failed to attach bridge /soc@...hy@...b000 to encoder TMDS-31: -16
	
> and this can also manifest itself as a NULL-pointer dereference:
> 
> 	[    7.339447] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
> 	
> 	[    7.643705] pc : drm_bridge_attach+0x70/0x1a8 [drm]

#regzbot ^introduced: 2bcca96abfbf

It looks like it may have been possible to hit this also before commit
2bcca96abfbf ("soc: qcom: pmic-glink: switch to DRM_AUX_HPD_BRIDGE") and
the transparent bridge rework in 6.8-rc1 even if that has not yet been
confirmed.

The above is what made this trigger since 6.8-rc1 however.

Johan