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

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Dec 10, 2014 at 02:53:01PM +0100, Daniel Vetter wrote:
> 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@chris-wilson.co.uk>
> > > > Cc: stable@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.

Or someone can dig out my old fb->offsets[] handling patch (and double check
that it's sane, fixing if not).

-- 
Ville Syrjälä
Intel OTC
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