Re: [PATCH] drm/exynos: fix vblank handling during dpms off

On Thu, Oct 09, 2014 at 02:43:02PM +0900, Alexandre Courbot wrote:

But there might be another issue, which is that calls to drm_vblank_get() will return -EINVAL if invoked between drm_blank_off and drm_blank_on. Is this really the desired behavior? Can it at least happen? If so, how are drivers supposed to react to this situation?

I've not yet seen the commit which causes this problem, but I hope that drm_wait_vblank() isn't affected by this. In current mainline, drm_vblank_get() is used inside drm_wait_vblank(), which is called as a result of userspace calling DRM_IOCTL_WAIT_VBLANK.

So, what is the effect of this change on user applications making use of the vblank wait ioctl - and is that change intended?