[PATCH] Fix a panic with 1M of shared memory, no GTT entries

[Lubomir Rintel <lkundrak@v3.sk>]

When GTT size is equal to amount of video memory, the amount of GTT
entries is computed lower than zero, which is invalid and leads to
off-by-one error in intel_i915_configure()

Originally posted here:
http://bugzilla.kernel.org/show_bug.cgi?id=12539
http://bugzilla.redhat.com/show_bug.cgi?id=445592

Signed-Off-By: Lubomir Rintel <lkundrak@v3.sk>
---
 drivers/char/agp/intel-agp.c |    8 +++++---
 1 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/char/agp/intel-agp.c b/drivers/char/agp/intel-agp.c
index c771418..4373adb 100644
--- a/drivers/char/agp/intel-agp.c
+++ b/drivers/char/agp/intel-agp.c
@@ -633,13 +633,15 @@ static void intel_i830_init_gtt_entries(void)
 			break;
 		}
 	}
-	if (gtt_entries > 0)
+	if (gtt_entries > 0) {
 		dev_info(&agp_bridge->dev->dev, "detected %dK %s memory\n",
 		       gtt_entries / KB(1), local ? "local" : "stolen");
-	else
+		gtt_entries /= KB(4);
+	} else {
 		dev_info(&agp_bridge->dev->dev,
 		       "no pre-allocated video memory detected\n");
-	gtt_entries /= KB(4);
+		gtt_entries = 0;
+	}
 
 	intel_private.gtt_entries = gtt_entries;
 }
-- 
1.5.5.6