drm/i915: Verify that our stolen memory doesn't conflict

Sanity check that the memory region found through the Graphics Base
of Stolen Memory is reserved and hidden from the rest of the system
through the use of the resource API.

v2: "Graphics Stolen Memory" is such a more bodacious name than the lame
    "i915 stolen", and convert to using devres for automagical cleanup of
    the resource. (danvet)
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
[danvet: Dump proper hexcodes.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem_stolen.c

@@ -46,6 +46,7 @@ static unsigned long i915_stolen_to_physical(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct pci_dev *pdev = dev_priv->bridge_dev;
+	struct resource *r;
 	u32 base;
 
 	/* On the machines I have tested the Graphics Base of Stolen Memory
@@ -88,6 +89,22 @@ static unsigned long i915_stolen_to_physical(struct drm_device *dev)
 #endif
 	}
 
+	if (base == 0)
+		return 0;
+
+	/* Verify that nothing else uses this physical address. Stolen
+	 * memory should be reserved by the BIOS and hidden from the
+	 * kernel. So if the region is already marked as busy, something
+	 * is seriously wrong.
+	 */
+	r = devm_request_mem_region(dev->dev, base, dev_priv->gtt.stolen_size,
+				    "Graphics Stolen Memory");
+	if (r == NULL) {
+		DRM_ERROR("conflict detected with stolen region: [0x%08x - 0x%08x]\n",
+			  base, base + (uint32_t)dev_priv->gtt.stolen_size);
+		base = 0;
+	}
+
 	return base;
 }