[Intel-gfx] [PATCH] drm/i915: Quietly reject attempts to create non-pagealigned stolen objects

[Daniel Vetter]

On Wed, Dec 10, 2014 at 11:13:28AM +0000, Chris Wilson wrote:
> On Wed, Dec 10, 2014 at 11:23:44AM +0100, Daniel Vetter wrote:
> > On Wed, Dec 10, 2014 at 08:17:11AM +0000, Chris Wilson wrote:
> > > This added as a BUG_ON as it considered that no one would ever request
> > > an unaligned object. However, it turns out that some BIOSes will
> > > allocate a scanout that is offset from 0 and not aligned to a page
> > > boundary, and we were passing this through and hitting the BUG_ON during
> > > boot.
> > > 
> > > Quietly reject such a request to reserve the unaligned stolen object and
> > > let the boot continue, restoring previous behaviour (i.e. no BIOS
> > > framebuffer preservation).
> > > 
> > > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=86883
> > > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > > Cc: stable at vger.kernel.org
> > > ---
> > >  drivers/gpu/drm/i915/i915_gem_stolen.c | 10 ++++++----
> > >  1 file changed, 6 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/i915_gem_stolen.c b/drivers/gpu/drm/i915/i915_gem_stolen.c
> > > index 5c616ec2c5c8..a3bc0fa07c6c 100644
> > > --- a/drivers/gpu/drm/i915/i915_gem_stolen.c
> > > +++ b/drivers/gpu/drm/i915/i915_gem_stolen.c
> > > @@ -646,13 +646,15 @@ i915_gem_object_create_stolen_for_preallocated(struct drm_device *dev,
> > >  	DRM_DEBUG_KMS("creating preallocated stolen object: stolen_offset=%x, gtt_offset=%x, size=%x\n",
> > >  			stolen_offset, gtt_offset, size);
> > >  
> > > -	/* KISS and expect everything to be page-aligned */
> > > -	BUG_ON(stolen_offset & 4095);
> > > -	BUG_ON(size & 4095);
> > > -
> > >  	if (WARN_ON(size == 0))
> > >  		return NULL;
> > >  
> > > +	/* KISS and expect everything to be GTT page-aligned */
> > > +	if ((stolen_offset | size) & 4095) {
> > 
> > Imo we should stil WARN_ON and fixup up the takeover code to align things
> > properly ...
> 
> You shot down my idea for storing deltas into objects in the past...
> 
> The BIOS scanout is properly aligned to the rules of the display engine,
> just not according to our mm restrictions. The bigger question is
> whether our 1:1 offset-to-stolen mapping is correct. It could well be
> that that the framebuffer is at stolen address 0, but just has a GTT
> offset.
> 
> So the only question is whether we reject the object reservation at the
> stolen layer or at the plane config layer. I decided that stolen was
> better, because it is failing to meet our mm restrictions not
> hardware restrictions.

The framebuffer layer can very much cope with offsets, so no need to
reject it. We just need to patch up the framebuffer we create a bit.
Offsets are in pixels but that should align well.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch