[Intel-gfx] [RFC 4/4] drm: add support for raw monotonic vblank timestamps

[Imre Deak]

On Fri, 2012-10-05 at 15:55 +0200, Michel Dänzer wrote:
> On Fre, 2012-10-05 at 16:37 +0300, Imre Deak wrote: 
> > In practice we never want the timestamps for vblank and page flip events
> > to be affected by time adjustments, so in addition to the gettimeofday
> > timestamps we used so far add support for raw monotonic timestamps.
> > 
> > For backward compatibility use flags to select between the old and new
> > timestamp format.
> > 
> > Note that with this change we will save the timestamp in both formats,
> > for cases where multiple clients are expecting an event notification in
> > different time formats.
> 
> I wonder if all this trouble is really necessary. I honestly can't
> imagine any user of this API requiring non-monotonic timestamps and
> breaking with monotonic ones. I think it was simply a mistake that we
> didn't make them monotonic in the first place (or maybe it wasn't even
> possible when this API was first introduced).

Yea, I'd rather simply switch over to monotonic timestamps too. But that
would break apps that already compare against the wall time for whatever
purpose (for example A/V sync).

--Imre