[Intel-gfx] [PATCH] drm/i915: set persistent mode for fbc

[Chris Wilson]

On Fri,  1 Jul 2011 12:48:43 -0700, Ben Widawsky <ben at bwidawsk.net> wrote:
> This seems to fix my bugs with sna enabled.
> 
> We should collect some power numbers, and validate it works on ILK
> before upstreaming. (And read more about what it actually does).

The hints that I've read indicate that persistent mode is to be used with
front-buffer rendering, ala X. Page-flipping always causes a
recompression, so I'm not sure what the design for the non-persistent mode
is for, but maybe it helps save power in the page-flipping case. Inferring
further, I suspect it is whether the SA monitors the usage of the fence
associated with the scanout for direct modifications by the CPU.

Intrigued to know what the power numbers are, but it appears that we
cannot live without this bit set on SNB. So it is a case of whether
enabling FBC is a power-conservation for us at all... Unless we clear that
bit upon a page-flip and then reset it after the following vblank (with no
intervening flips).

Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre