[adding a few people and lists to the recipients]
Hi! Thx for your rpeort.
On 27.07.24 18:07, kevin@holm.dev wrote:
Connecting two 4k displays with display port through a lenovo usb-c dock (type 40AS) to a Lenovo P14s Gen 2 (type 21A0) results in no image on the connected displays.
The CPU in the Lenovo P14s is a 'AMD Ryzen 7 PRO 5850U with Radeon Graphics' and it has no discrete GPU.
I first noticed the issue with kernel version '6.10.0-arch1-2' provided by arch linux. With the previous kernel version '6.9.10.arch1-1' both connected displays worked normally. I reported the issue in the arch forums at https://bbs.archlinux.org/viewtopic.php?id=297999 and was guided to do a bisection to find the commit that caused the problem. Through testing I identified that the issue is not present in the latest kernel directly compiled from the trovalds/linux git repository.
With git bisect I identified 4df96ba66760345471a85ef7bb29e1cd4e956057
That's 4df96ba6676034 ("drm/amd/display: Add timing pixel encoding for mst mode validation") [v6.10-rc1] from Hersen Wu.
Did you try if reverting that commit is possible and might fix the problem?
as the first bad commit and fa57924c76d995e87ca3533ec60d1d5e55769a27
That's fa57924c76d995 ("drm/amd/display: Refactor function dm_dp_mst_is_port_support_mode()") [v6.10-post] from Wayne Lin.
as the first commit that fixed the problem again.
Hmm, the latter commit does not have a fixes tag and might or might not be to invasive to backport to 6.10. Let's see what the AMD developers say.
The initial commit only still shows an image on one of the connected 4k screens. I have not investigated further to find out at what point both displays stopped showing an image.
Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat) -- Everything you wanna know about Linux kernel regression tracking: https://linux-regtracking.leemhuis.info/about/#tldr If I did something stupid, please tell me, as explained on that page.