Re: [PATCH] drm/i915: BIOS and power context stolen mem handling for VLV v6

[Jesse Barnes <jbarnes@virtuousgeek.org>]

On Tue, 7 May 2013 22:57:37 +0100
Chris Wilson <chris@chris-wilson.co.uk> wrote:

> On Tue, May 07, 2013 at 02:34:31PM -0700, Jesse Barnes wrote:
> > +static void valleyview_setup_pctx(struct drm_device *dev)
> > +{
> > +	struct drm_i915_private *dev_priv = dev->dev_private;
> > +	struct drm_i915_gem_object *pctx;
> > +	unsigned long pctx_paddr;
> > +	u32 pcbr;
> > +	int pctx_size = 24*1024;
> > +
> > +	pcbr = I915_READ(VLV_PCBR);
> > +	if (pcbr) {
> > +		/* BIOS set it up already, grab the pre-alloc'd space */
> > +		int pcbr_offset;
> > +
> > +		pcbr_offset = (pcbr & (~4095)) - dev_priv->mm.stolen_base;
> > +		pctx = i915_gem_object_create_stolen_for_preallocated(dev_priv->dev,
> > +								      pcbr_offset,
> > +								      pcbr_offset,
> > +								      pctx_size);
> 
> We're reserving global GTT space here for someting that just looks like
> it requires contiguous physical memory. This may cause issues if
> something else is already bound to that GTT range. I think we want to
> extend the interface to not reserve GTT space if gtt_offset == -1.

I should have added a comment for this too.  The physical range for the
power context must reside in stolen space.  So while it needs
contiguous physical memory, it also has a relationship to the stolen
handling.  I'd prefer to see a failure here than to try to do something
fancy with funky GTT vs stolen setups...  (Still waiting on the BIOS
guys to promise the identity map going forward.)

-- 
Jesse Barnes, Intel Open Source Technology Center