Re: [PATCH 4/4] drm/i915: Reserve space for FBC (fbcon)

[Ben Widawsky <ben@bwidawsk.net>]

On Thu, Jun 19, 2014 at 08:28:11PM +0100, Chris Wilson wrote:
> On Thu, Jun 19, 2014 at 12:06:13PM -0700, Ben Widawsky wrote:
> > This is one part in a few fixes needed to make FBC work with limited
> > stolen memory and large resolution displays. It is not the full
> > solution, but one (easy) step.
> > 
> > The patch is straight-forward, it attempts to check there will be room
> > for FBC before trying to "reclaim"
> 
> But it special cases one particular allocation. Why don't you just
> reserve stolen upfront for FBC? Compute the maximum buffer size the
> hardware could support and try to claim it during stolen init.
> -Chris
> 

This was my initial thought actually. I didn't want to have to rework
all of our initialization sequence, and verify I didn't break anything.
In particular I wasn't sure what happens when we try to recover the fb
from stolen (if it fails).

In particular, there is a logical conflict between fastboot and fbc -
and one needs to assign the preference over who gets stolen memory
first. Also, when I wrote this patch, I was unaware that the reclaimed
fb by itself was enough to not allow the full CFB to fit (though it will
with the 3 patches before this)

Anyway, consider this the demonstration of the problem, and [my only]
half-attempt to fix it. Hopefully you guys can fix it properly.

-- 
Ben Widawsky, Intel Open Source Technology Center