Bug 1402293

The problem doesn't occur after upgrading xorg-x11-drv-ati in Fedora 23 to 7.6.1-3.20160215, which has the same git date as the F24 package, which exhibits the problem when F24 is running.

Moreover, upgrading the F23 kernel from 4.2.3-300 to 4.8.11-100 caused the problem to occur on F23.

So the problem looks to be in the kernel package rather than the xorg-x11-drv-ati package.

I'd like some help trying to bisect by installing different F23 kernel packages. 

I've found a history here:

https://repos.fedorapeople.org/repos/thl/kernel-vanilla-fedora/fedora-23/history

but I'd appreciate some help on how to install an arbitrary one of these. I've been unsuccessful in my attempts with dnf. Are all these kernel versions still in a repository somewhere, or will I have to do a git bisect with compiles?

Thanks.

Please see https://fedoraproject.org/wiki/KernelBugTriage#Video_Subsystem_bugs for why the component was changed to xorg-x11-drv-ati. You may have better luck with http://koji.fedoraproject.org/koji/packageinfo?packageID=8 for finding appropriate kernels.

OK. Thank you Laura.

While I wasn't able to install old kernels directly from the koji repos, I was able to download them via commands like

wget -r -np -nd -R '*debug*','index*' http://kojipkgs.fedoraproject.org/packages/kernel/4.5.5/200.fc23/x86_64/

then

dnf install *

The result is that the last working kernel is 4.5.4-200, and 4.5.5-200 exhibits the problem.

I'll now look to see what commits could be the cause.

Note: Often, rather than a noisy display, the problem causes the display to go black (hang?) during boot, requiring a reboot to try again.

Looking at the 4.5.5 changelog https://www.kernel.org/pub/linux/kernel/v4.x/ChangeLog-4.5.5 , there are three radeon commits:

drm/radeon: fix DP mode validation
https://github.com/torvalds/linux/commit/ff0bd441bdfbfa09d05fdba9829a0401a46635c1

drm/radeon: fix DP link training issue with second 4K monitor
https://github.com/torvalds/linux/commit/1a738347df2ee4977459a8776fe2c62196bdcb1b

and

drm/radeon: fix PLL sharing on DCE6.1 (v2)
https://github.com/torvalds/linux/commit/e3c00d87845ab375f90fa6e10a5e72a3a5778cd3

Reversing all three patches didn't fix the problem, including a fourth patch that does the same as the first but for GPUs embedded in AMD CPUs (which is the hardware I have):

https://github.com/torvalds/linux/commit/c47b9e0944e483309d66c807d650ac8b8ceafb57#diff-c9c35e6d6def5e31f48356c03ca18a1b

So the problem must lie in either another vanilla patch or another Fedora-only patch.

Sorry, I needed to run "dracat" to make sure the new modules loaded on boot (then had a struggle with magic numbers).

I've verified that the problem goes away when only this commit is reversed:

drm/radeon: fix DP mode validation
https://github.com/torvalds/linux/commit/ff0bd441bdfbfa09d05fdba9829a0401a46635c1

It wouldn't be easy for me to work out what code fixes my problem without re-introducing the original problem:

https://bugs.freedesktop.org/show_bug.cgi?id=95206

The freedesktop.org bug for this is

https://bugs.freedesktop.org/show_bug.cgi?id=99326

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