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From: kevin@holm.dev Message-ID: TLS-Required: No Subject: Re: [REGRESSION] No image on 4k display port displays connected through usb-c dock in kernel 6.10 To: "Linux regressions mailing list" , "Alex Deucher" , "Hersen Wu" , "Wayne Lin" Cc: regressions@lists.linux.dev, stable@vger.kernel.org, "LKML" , "ML dri-devel" , amd-gfx@lists.freedesktop.org In-Reply-To: <9ca719e4-2790-4804-b2cb-4812899adfe8@leemhuis.info> References: <9ca719e4-2790-4804-b2cb-4812899adfe8@leemhuis.info> X-Migadu-Flow: FLOW_OUT > [adding a few people and lists to the recipients] >=20 >=20Hi! Thx for your rpeort. >=20 >=20On 27.07.24 18:07, kevin@holm.dev wrote: >=20 >=20>=20 >=20> Connecting two 4k displays with display port through a lenovo usb-c > >=20 >=20> dock (type 40AS) to a Lenovo P14s Gen 2 (type 21A0) results in no > >=20 >=20> image on the connected displays. > >=20 >=20>=20=20 >=20>=20 >=20> The CPU in the Lenovo P14s is a 'AMD Ryzen 7 PRO 5850U with Radeon > >=20 >=20> Graphics' and it has no discrete GPU. > >=20 >=20>=20=20 >=20>=20 >=20> I first noticed the issue with kernel version '6.10.0-arch1-2' > >=20 >=20> provided by arch linux. With the previous kernel version > >=20 >=20> '6.9.10.arch1-1' both connected displays worked normally. I report= ed > >=20 >=20> the issue in the arch forums at > >=20 >=20> https://bbs.archlinux.org/viewtopic.php?id=3D297999 and was guided= to > >=20 >=20> do a bisection to find the commit that caused the problem. Through > >=20 >=20> testing I identified that the issue is not present in the latest > >=20 >=20> kernel directly compiled from the trovalds/linux git repository. > >=20 >=20>=20=20 >=20>=20 >=20> With git bisect I identified 4df96ba66760345471a85ef7bb29e1cd4e956= 057 > >=20 >=20 > That's 4df96ba6676034 ("drm/amd/display: Add timing pixel encoding for >=20 >=20mst mode validation") [v6.10-rc1] from Hersen Wu. >=20 >=20Did you try if reverting that commit is possible and might fix the pr= oblem? Reverting is not easily possible: $ git checkout v6.10 [...] HEAD is now at 0c3836482481 Linux 6.10 $ git revert 4df96ba66760345471a85ef7bb29e1cd4e956057 Auto-merging drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c CONFLICT (content): Merge conflict in drivers/gpu/drm/amd/display/amdgpu_= dm/amdgpu_dm_mst_types.c error: could not revert 4df96ba66760... drm/amd/display: Add timing pixel= encoding for mst mode validation I do not know enough to try and solve the conflict myself without breakin= g more things. >=20 >=20>=20 >=20> as the first bad commit and fa57924c76d995e87ca3533ec60d1d5e55769a2= 7 > >=20 >=20 > That's fa57924c76d995 ("drm/amd/display: Refactor function >=20 >=20dm_dp_mst_is_port_support_mode()") [v6.10-post] from Wayne Lin. >=20 >=20>=20 >=20> as the first commit that fixed the problem again. > >=20 >=20 > Hmm, the latter commit does not have a fixes tag and might or might not >=20 >=20be to invasive to backport to 6.10. Let's see what the AMD developers= say. >=20 >=20>=20 >=20> The initial commit only still shows an image on one of the connecte= d > >=20 >=20> 4k screens. I have not investigated further to find out at what po= int > >=20 >=20> both displays stopped showing an image. > >=20 >=20 > Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat= ) >=20 >=20-- >=20 > Everything you wanna know about Linux kernel regression tracking: >=20 >=20https://linux-regtracking.leemhuis.info/about/#tldr >=20 >=20If I did something stupid, please tell me, as explained on that page. >