drm/i915: allow stolen, pre-allocated objects to avoid GTT allocation v2

In some cases, we may not need GTT address space allocated to a stolen
object, so allow passing -1 to the preallocated function to indicate as
much.

v2: remove BUG_ON(gtt_offset & 4095) now that -1 is allowed (Ville)

Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem_stolen.c

@@ -339,7 +339,6 @@ i915_gem_object_create_stolen_for_preallocated(struct drm_device *dev,
 
 	/* KISS and expect everything to be page-aligned */
 	BUG_ON(stolen_offset & 4095);
-	BUG_ON(gtt_offset & 4095);
 	BUG_ON(size & 4095);
 
 	if (WARN_ON(size == 0))
@@ -360,6 +359,10 @@ i915_gem_object_create_stolen_for_preallocated(struct drm_device *dev,
 		return NULL;
 	}
 
+	/* Some objects just need physical mem from stolen space */
+	if (gtt_offset == -1)
+		return obj;
+
 	/* To simplify the initialisation sequence between KMS and GTT,
 	 * we allow construction of the stolen object prior to
 	 * setting up the GTT space. The actual reservation will occur

drivers/gpu/drm/i915/intel_pm.c

@@ -2881,7 +2881,7 @@ static void valleyview_setup_pctx(struct drm_device *dev)
 		pcbr_offset = (pcbr & (~4095)) - dev_priv->mm.stolen_base;
 		pctx = i915_gem_object_create_stolen_for_preallocated(dev_priv->dev,
 								      pcbr_offset,
-								      pcbr_offset,
+								      -1,
 								      pctx_size);
 		goto out;
 	}