[Bug 18542] [PATCH] Textured Video (XV) tearing.

[bugzilla-daemon at freedesktop.org]

http://bugs.freedesktop.org/show_bug.cgi?id=18542





--- Comment #12 from Alex Deucher <agd5f at yahoo.com>  2008-11-20 09:08:41 PST ---
(In reply to comment #11)
> Ah, I see. So the time we have is just the period between scan lines, not
> between screen updates? I guess that can be quite brief, especially with
> reduced blanking (or does that just affect vblank?).
> 

Basically what the patch does is at the start of an acceleration call, I stall
the engine until we get to the rising or falling edge or a particular vline. 
The vline I chose was the last one of the visible portion of the scanout
buffer.  At that point the display controller should be at the start of the
blanking period; the stall drops and rendering continues.  Hopefully it
finishes before the blanking period ends.  If not you get tearing again;
possibly in a different place.  There's no real clean way to do this without
pageflipping.  Reduced blanking does reduce the length of the blanking period
so you have less time to work with.

> If I'm going to go elbow deep into this, any good pointer into the reference
> docs about this?
> 

The driver code and the chip documentation here:
http://www.x.org/docs/AMD/


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