[PATCH] drm/drm_vblank: use drm_warn_once() to warn undefined mode timing

[Shawn Guo]

On Mon, Oct 19, 2020 at 05:48:29PM +0200, Daniel Vetter wrote:
> On Fri, Oct 16, 2020 at 07:46:41PM +0800, Shawn Guo wrote:
> > Indeed!  Adding drm_crtc_vblank_reset() into driver crtc reset hook
> > removes the WARNING for me.  Really appreciate your comments, Daniel!
> 
> This should work automatically if you're using the atomic state helpers.
> Please try to unify as much as possible, so you're not missing any future
> bugfixes in this area. Although I thought I've completely reviewed all
> drivers to fix as many as possible for this bug. Are you on some older
> kernel that didn't have this? Maybe good idea to submit the bugfix in
> upstream to stable, if that's the case.

Yes, I'm running a 4.19 stable kernel with msm/mdp5 device.  The bug was
addressed (unintentionally?) by one patch that is part of the series
adding Nexus 5 display support.  And later on, you commit 51f644b40b4b
("drm/atomic-helper: reset vblank on crtc reset") switches the driver to
use atomic state helper.

Shawn

[1] https://lore.kernel.org/patchwork/patch/1082564/