From: Brandon Philips <bphilips@suse.de>
Subject: Avoid oops on G33 in 1MB stolen Mem case
References: bnc#391261
Patch-Mainline: soon (see bug for ref)

This is similar to f443675affe3f16dd428e46f0f7fd3f4d703eeab which was
reverted because it broke with older XOrg driver. This patch only fixes
the 1MB stolen case since it causes an oops due to a calculation
problem.

This will not work with older X drivers without the accompanying patch
but I think avoiding an oops and making it possible to work with an
up-to-date xorg driver is reasonable.

Explanation of the oops:

> static void intel_i830_init_gtt_entries(void)
...
>         } else if (IS_G33) {
>         /* G33's GTT size defined in gmch_ctrl */
>                 switch (gmch_ctrl & G33_PGETBL_SIZE_MASK) {
>                 case G33_PGETBL_SIZE_1M:
>                         size = 1024;
>                         break;
...
>                 size += 4;

size = 1028

Then since we have the BIOS setting 1MB for the device in the GMCH
control we get to here:

>         } else {
>                 switch (gmch_ctrl & I855_GMCH_GMS_MASK) {
>                 case I855_GMCH_GMS_STOLEN_1M:
>                         gtt_entries = MB(1) - KB(size);
>                         break;

MB(1) = 1 * 1024 * 1024
KB(1028) = 1028 * 1024

MB(1) - KB(1028) = -4096

>         gtt_entries /= KB(4);
>         intel_private.gtt_entries = gtt_entries;

We end up with -1 in gtt_entries.

This leads to intel_i915_configure reading/writing to areas outside of
mapped memory and the oops.

Signed-off-by: Brandon Philips <bphilips@suse.de>
Acked-by: Thomas Renninger <trenn@suse.de>

---
 drivers/char/agp/intel-agp.c |    7 +++++++
 1 file changed, 7 insertions(+)

--- a/drivers/char/agp/intel-agp.c
+++ b/drivers/char/agp/intel-agp.c
@@ -801,6 +801,13 @@ static void intel_i830_init_gtt_entries(
 	} else {
 		switch (gmch_ctrl & I855_GMCH_GMS_MASK) {
 		case I855_GMCH_GMS_STOLEN_1M:
+			if (IS_G33) {
+				size = 0;
+				printk(KERN_WARNING PFX
+				       "Warning: G33 chipset with 1MB"
+					" allocated. Older X.org Intel drivers"
+					" will not work.\n");
+			}
 			gtt_entries = MB(1) - KB(size);
 			break;
 		case I855_GMCH_GMS_STOLEN_4M:
