Comment 24 for bug 1899304

Before bisecting, I investigated the PCI issue:
https://bugs.launchpad.net/bugs/1902795

I've faced the PCI issue before the AGP one, but it was less critical. I've submitted a patch that may fix some issues (with drawback of being non-optimal on platforms were PCI graphics are known to already work) but not everything is fixed. To be clear: that does not fix PCI GPU failure on K8 / K10 neither AGP-as-PCI failure, but that is at least a step forward, and would help specialists to investigate more the issue. At this point I may have reached my skill cap on such topic.

Because PCI and AGP-as-PCI behaves differently and the later code may have specific bugs, I opened an issue dedicated to track bugs when AGP cards are driven as PCI ones:
https://bugs.launchpad.net/bugs/1902981

I did not bisected anything after having identified the breakage was introduced by 5.9-rc1, and I directly tried to revert commit ba806f98f868ce107aa9c453fef751de9980e4af that disabled AGP at kernel build. I reverted this commit over the 5.10-rc2 tag from the torvalds branch and both the ATI Radeon HD 4670 on the K10 computer and the ATI Radeon X1950 PRO on the AMD K8 computer started to work again immediately. Game performance was as expected and desktop experience was really smooth like we can expect from such aging but high end hardware from its time.

It looks like I misread your first comment, I believed you were asking me to try the 5.10-rc1 build like if that commit was already reverted (the only action that seems to be able to fix the issue at this point).

After this commit is reverted, I have not yet noticed the other issues I've reported (disk IO seems to be OK, I have not tested audio yet), so the other ones may have been collateral damage of the AGP/PCI one.

So, you were right, the regression was introduced by the "drm/radeon: disable AGP by default" commit. It sounds too early to disable without alternative some hardware that was still sold as brand new in 2012 (the ATI Radeon HD 4670 AGP was).