i915 boot regression on Q35 chipset with 2.6.35-rc4

[Tim Gardner <tim.gardner@canonical.com>]

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Dave,

Please find attached a patch that fixes a boot time regression caused by 
commit f1befe71fa7a79ab733011b045639d8d809924ad. It has been reported to 
fix at least one user's boot problems.

I think it is also likely the source of the problems reported in 
http://marc.info/?l=linux-kernel&m=127869783002454&w=2

rtg
-- 
Tim Gardner tim.gardner@canonical.com

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>From e025bfb96059be648074a02f60dff92fb658cb9a Mon Sep 17 00:00:00 2001
From: Tim Gardner <tim.gardner@canonical.com>
Date: Fri, 9 Jul 2010 11:14:41 -0600
Subject: [PATCH] i915: Use the correct mask to detect i830 aperture size.

BugLink: https://bugs.launchpad.net/bugs/597075

commit f1befe71fa7a79ab733011b045639d8d809924ad introduced a regression when
detecting aperture size of some i915 adapters, e.g., those on the
Intel Q35 chipset.

The original report: https://bugzilla.kernel.org/show_bug.cgi?id=15733
The regression report: https://bugzilla.kernel.org/show_bug.cgi?id=16294

According to the specification found at http://intellinuxgraphics.org/VOL_1_graphics_core.pdf,
the PCI config space register I830_GMCH_CTRL is a mirror of GMCH Graphics Control. The correct
macro for isolating the aperture size bits is therefore I830_GMCH_GMS_MASK along with the
attendant changes to the case statement.

Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Tested-by: Kees Cook <kees.cook@canonical.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Eric Anholt <eric@anholt.net>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
---
 drivers/char/agp/intel-gtt.c |   13 ++++++++-----
 1 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/char/agp/intel-gtt.c b/drivers/char/agp/intel-gtt.c
index 9344216..a754715 100644
--- a/drivers/char/agp/intel-gtt.c
+++ b/drivers/char/agp/intel-gtt.c
@@ -1216,17 +1216,20 @@ static int intel_i915_get_gtt_size(void)
 
 		/* G33's GTT size defined in gmch_ctrl */
 		pci_read_config_word(agp_bridge->dev, I830_GMCH_CTRL, &gmch_ctrl);
-		switch (gmch_ctrl & G33_PGETBL_SIZE_MASK) {
-		case G33_PGETBL_SIZE_1M:
+		switch (gmch_ctrl & I830_GMCH_GMS_MASK) {
+		case I830_GMCH_GMS_STOLEN_512:
+			size = 512;
+			break;
+		case I830_GMCH_GMS_STOLEN_1024:
 			size = 1024;
 			break;
-		case G33_PGETBL_SIZE_2M:
-			size = 2048;
+		case I830_GMCH_GMS_STOLEN_8192:
+			size = 8*1024;
 			break;
 		default:
 			dev_info(&agp_bridge->dev->dev,
 				 "unknown page table size 0x%x, assuming 512KB\n",
-				(gmch_ctrl & G33_PGETBL_SIZE_MASK));
+				(gmch_ctrl & I830_GMCH_GMS_MASK));
 			size = 512;
 		}
 	} else {
-- 
1.7.0.4