Bug 200667 - [AMDGPU] stacktrace in dmesg, starting at drm_dp_i2c_do_msg
Summary: [AMDGPU] stacktrace in dmesg, starting at drm_dp_i2c_do_msg
Status: NEW
Alias: None
Product: Drivers
Classification: Unclassified
Component: Video(DRI - non Intel) (show other bugs)
Hardware: All Linux
: P1 normal
Assignee: drivers_video-dri
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2018-07-27 11:54 UTC by Christian Widmer
Modified: 2018-10-22 21:14 UTC (History)
2 users (show)

See Also:
Kernel Version: 4.17.10
Subsystem:
Regression: No
Bisected commit-id:


Attachments
Full dmesg output from kernel 4.18-r6 (89.90 KB, text/plain)
2018-07-27 11:54 UTC, Christian Widmer
Details
Kernel configuration (96.83 KB, text/plain)
2018-07-27 11:55 UTC, Christian Widmer
Details
lspci (22.55 KB, text/plain)
2018-07-27 11:56 UTC, Christian Widmer
Details

Description Christian Widmer 2018-07-27 11:54:34 UTC
Created attachment 277569 [details]
Full dmesg output from kernel 4.18-r6

When I changed my kernel from 4.17.9 to 4.17.10 (both patched with the Gentoo patchset), a stacktrace started to appear in the kernel messages. To check whether this is still an issue in mainline and not related to the distribution kernel, I tried 4.18-r6 which also shows the issue.
Comment 1 Christian Widmer 2018-07-27 11:55:07 UTC
Created attachment 277571 [details]
Kernel configuration
Comment 2 Christian Widmer 2018-07-27 11:56:17 UTC
Created attachment 277573 [details]
lspci

I am using an RX 580.
Comment 3 Christian Widmer 2018-07-27 12:03:17 UTC
I might add simply booting the kernel is all that is needed to trigger the issue. The stacktraces automatically appear during the boot process.
Comment 4 Alex Deucher 2018-07-27 14:41:25 UTC
Can you bisect?
Comment 5 Christian Widmer 2018-07-27 17:47:29 UTC
The bisect identified commit 9168c089a2122606e2c01f6fbeda85ff950ac189 (Revert "drm/amd/display: Don't return ddc result and read_bytes in same return value", upstream commit 5292221d6ddfed75e5b46cd42237a677094b99f3). And a quick test with reverting this change in my distribution's 4.17.10 kernel and in the mainline 4.18-rc6 kernel indeed made the stacktrace disappear.
Comment 6 Alex Deucher 2018-07-27 17:55:16 UTC
The warning is harmless.  As per the commit message, this is fixed properly for 4.19 with the following patches:

    This breaks DDC in certain cases.  Revert for 4.18 and previous kernels.
    For 4.19, this is fixed with the following more extensive patches:
    drm/amd/display: Serialize is_dp_sink_present
    drm/amd/display: Break out function to simply read aux reply
    drm/amd/display: Return aux replies directly to DRM
    drm/amd/display: Right shift AUX reply value sooner than later
    drm/amd/display: Read AUX channel even if only status byte is returned
Comment 7 Christian Widmer 2018-07-27 18:39:21 UTC
For the sake of completeness I have just tested linux-next which contains all those patches and the warning is indeed gone. Thank you for your responses!
Comment 8 Christian Widmer 2018-10-22 21:14:53 UTC
As expected, the warning is indeed gone with the recently released stable kernel 4.19.

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