[PATCH 5/6] drm: Prevent vblank counter jumps with timestamp based update method.

[Mario Kleiner]

On 02/10/2016 06:17 PM, Daniel Vetter wrote:
> On Wed, Feb 10, 2016 at 5:28 PM, Mario Kleiner
> <mario.kleiner.de at gmail.com> wrote:
>> There's another scenario where this zero-ts case can be hit. If the driver
>> drm_vblank_init()'s - setting all timestamps to zero - and then code starts
>> using vblanks (drm_vblank_get()) without drm_vblank_on beforehand, which is
>> afaics the case with nouveau. Unless that's considered an error as well,
>> we'd need to init the timestamps to something non-zero but harmless like 1
>> usecs at drm_vblank_init() time?
>
> Both legacy modeset helpers and atomic ones assume by default that you
> start out with everything disabled. Pre-atomic drivers make that
> happen by calling disable_unused_functions() to shut down anything the
> bios has enabled. I think this can't happen.
>
> For drivers that do take over bootloader display config they must call
> vblank_on explicitly themselves, which i915 does.
>
>> What makes sense as output here? DRM_WARN_ONCE?
>
> I'd go with WARN_ON and tune it down if it's offensive. But WARN_ON
> patch for 4.6 of course.
> -Daniel
>

Ok, so does this one have your R-b for stable as is? What about a proper 
nouveau fix if i find one? Probably also for 4.6 then, given that this 
patch fixes it up good enough for stable?

-mario