[Intel-gfx] [PATCH] drm/i915: fix stolen bios_reserved checks

[Chris Wilson]

On Mon, Aug 10, 2015 at 02:57:32PM -0300, Paulo Zanoni wrote:
> I started digging this when I noticed that the BDW code was just
> reserving 1mb by coincidence since it was reading reserved fields.
> Then I noticed we didn't have any values set for SNB and earlier, and
> that the HSW sizes were wrong. After that, I noticed that the reserved
> area has a specific start, and may not exactly end where the stolen
> memory ends. I also noticed the base pointer can be zero. So I decided
> to just write a single patch fixing everything instead of 20 patches
> that would be much harder to review.
> 
> This patch may solve random stolen memory corruption/problems on
> almost all platforms. Notice that since this is always dealing with
> the top of the stolen memory, the problems are not so easy to
> reproduce - especially since FBC is still disabled by default.
> 
> One of the major differences of this patch is that we now look at both
> the size and base address. By only looking at the size we were
> assuming that the reserved area was always at the very top of
> stolen, which is not always true.
> 
> After we merge the patch series that allows user space to allocate
> stolen memory we'll be able to write IGT tests that maybe catch the
> bugs fixed by this patch.
> 
> v2:
>   - s/BIOS reserved/stolen reserved/g (Chris)
>   - Don't DRM_ERROR if we can't do anything about it (Chris)
>   - Improve debug messages (Chris).
>   - Use the gen7 version instead of gen6 on HSW. Tom found some
>     documentation problems, so I think with gen7 we're on the safer
>     side (Tom).
> 
> Signed-off-by: Paulo Zanoni <paulo.r.zanoni at intel.com>

Looks ok to me, I'd push for DRM_INFO() for the amount of memory
available (since I think that is interesting as a user).

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

-- 
Chris Wilson, Intel Open Source Technology Centre