Re: [PATCH 8/9] drm/i915: treat no fb -> fb as simple flip instead of full mode set

[Chris Wilson <chris@chris-wilson.co.uk>]

On Wed, Mar 27, 2013 at 01:49:47PM +0100, Daniel Vetter wrote:
> On Wed, Mar 27, 2013 at 3:09 AM, Jesse Barnes <jbarnes@virtuousgeek.org> wrote:
> > If for example the BIOS fb is too small for the dual pipe config we detect,
> > we may have valid timings and such, but no fb. The pfit case also hits this
> > path (though currently only fastboots if you hack your mode clock to match).
> 
> But even when the BIOS fb is to small and the BIOS config uses the
> pfit, we /should/ have an fb around. Looking a bit closer I think the
> confusion stems from you reading out the adjusted mode, but treating
> it like the requested mode. I think it'd be much more solid if we
> store the read-out mode in the adjusted_mode (won't work otherwise
> with hw state cross-checking anyway), and then do two comparisons
> here:
> 
> - Does the request mode (plus everything else) match? If so, just do
> an fb_set_base call.
> - Does the adjusted mode match (plus the entire output routing ofc)?
> That means there's either the vga plane or a pfit in-between which we
> don't like. If possible we can then play some tricks to avoid the full
> modeset.
> 
> The reason that I'm a bit freaked about about your change here is that
> in a lot of places we treat crtc->fb == NULL as "no mode set". So I
> fear we're breaking a few too many assumptions here with that hack,
> and it simply needs more thought about what we should actually check.

The check here is why we were so enthusiastic about moving to a
pipe_config framework that could match up a configured pipe with an
invalid fb and then just exchange the fb.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre