agp: Fix stolen memory counting on G4X.

On the GM45, the amount of stolen memory mapped to the GTT was underestimated,
even though we had 508KB more available since the GTT doesn't take from
stolen memory. On the non-GM45 G4X, we overestimated how much stolen was
mapped to the GTT by 4KB, resulting in GPU page faults when that page was
accessed.

This update requires a corresponding update to xf86-video-intel to work
correctly.
Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/char/agp/intel-agp.c

@@ -54,8 +54,7 @@
 		 agp_bridge->dev->device == PCI_DEVICE_ID_INTEL_82965Q_HB || \
 		 agp_bridge->dev->device == PCI_DEVICE_ID_INTEL_82965G_HB || \
 		 agp_bridge->dev->device == PCI_DEVICE_ID_INTEL_82965GM_HB || \
-		 agp_bridge->dev->device == PCI_DEVICE_ID_INTEL_82965GME_HB || \
-		 agp_bridge->dev->device == PCI_DEVICE_ID_INTEL_GM45_HB)
+		 agp_bridge->dev->device == PCI_DEVICE_ID_INTEL_82965GME_HB)
 
 #define IS_G33 (agp_bridge->dev->device == PCI_DEVICE_ID_INTEL_G33_HB || \
 		agp_bridge->dev->device == PCI_DEVICE_ID_INTEL_Q35_HB || \
@@ -63,7 +62,8 @@
 
 #define IS_G4X (agp_bridge->dev->device == PCI_DEVICE_ID_INTEL_IGD_E_HB || \
 		agp_bridge->dev->device == PCI_DEVICE_ID_INTEL_Q45_HB || \
-		agp_bridge->dev->device == PCI_DEVICE_ID_INTEL_G45_HB)
+		agp_bridge->dev->device == PCI_DEVICE_ID_INTEL_G45_HB || \
+		agp_bridge->dev->device == PCI_DEVICE_ID_INTEL_GM45_HB)
 
 extern int agp_memory_reserved;
 
@@ -525,8 +525,10 @@ static void intel_i830_init_gtt_entries(void)
 		size += 4;
 	} else if (IS_G4X) {
 		/* On 4 series hardware, GTT stolen is separate from graphics
-		 * stolen, ignore it in stolen gtt entries counting */
-		size = 0;
+		 * stolen, ignore it in stolen gtt entries counting.  However,
+		 * 4KB of the stolen memory doesn't get mapped to the GTT.
+		 */
+		size = 4;
 	} else {
 		/* On previous hardware, the GTT size was just what was
 		 * required to map the aperture.