[PATCH 2/2] Revert "drm/amd/display: disable CRTCs with NULL FB on their primary plane (V2)"

Michel Dänzer michel at daenzer.net
Fri Apr 13 07:15:23 UTC 2018

On 2018-04-13 04:55 AM, S, Shirish wrote:
> Hi Harry, Alex,
> The solution given while reviewing my patch was that "DC should support enabling a CRTC without a framebuffer."

I think it's weird that an enabled CRTC would end up having a NULL FB
during normal operation in the first place. Any idea how that happens?

> Since the revert is a temporary workaround to address issue at hand and considering the bigger regression it will cause on ChromeOS(explained below),
> I would strongly recommend that the revert should not be mainlined (to linus tree), until a proper fix for both the issues i.e., flickering and BUG hit on atomic is found.
> For the sake of everyone's understanding in the list below is a brief background.
> Mainline patch from intel folks, "846c7df drm/atomic: Try to preserve the crtc enabled state in drm_atomic_remove_fb, v2." 
> introduces a slight behavioral change to rmfb. Instead of disabling a crtc when the primary plane is disabled, it now preserves it.
> This change leads to BUG hit while performing atomic commit on amd driver leading to reboot/system instability on ChromeOS which has enabled
> drm atomic way of rendering, I also remember it causing some issue on other OS as well.

Can you provide more information about "some issue on other OS"?
Otherwise I'm afraid this is a no-brainer, since nobody's using ChromeOS
with an AMD GPU in the wild, whereas many people have been running into
issues with these commits in the wild, especially since they're in the
4.16 release.

Earthling Michel Dänzer               |               http://www.amd.com
Libre software enthusiast             |             Mesa and X developer

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