drm/i915: Respect GM965/GM45 bit-17-instead-of-bit-11 option for swizzling.

This fixes readpixels and buffer corruption when swapped out and in by
disabling tiling on them.

Now that we know that the bit 17 mode isn't just a mistake of older chipsets,
we'll need to work on a clever fix so that we can get the performance of
tiling on these chipsets, but that will require intrusive changes targeted
at the next kernel release, not this one.

Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/i915/i915_gem_tiling.c

@@ -119,9 +119,10 @@ i915_gem_detect_bit_6_swizzle(struct drm_device *dev)
 			    dcc & DCC_CHANNEL_XOR_DISABLE) {
 				swizzle_x = I915_BIT_6_SWIZZLE_9_10;
 				swizzle_y = I915_BIT_6_SWIZZLE_9;
-			} else if (IS_I965GM(dev) || IS_GM45(dev)) {
-				/* GM965 only does bit 11-based channel
-				 * randomization
+			} else if ((IS_I965GM(dev) || IS_GM45(dev)) &&
+				   (dcc & DCC_CHANNEL_XOR_BIT_17) == 0) {
+				/* GM965/GM45 does either bit 11 or bit 17
+				 * swizzling.
 				 */
 				swizzle_x = I915_BIT_6_SWIZZLE_9_10_11;
 				swizzle_y = I915_BIT_6_SWIZZLE_9_11;

drivers/gpu/drm/i915/i915_reg.h

@@ -522,6 +522,7 @@
 #define DCC_ADDRESSING_MODE_DUAL_CHANNEL_INTERLEAVED	(2 << 0)
 #define DCC_ADDRESSING_MODE_MASK			(3 << 0)
 #define DCC_CHANNEL_XOR_DISABLE				(1 << 10)
+#define DCC_CHANNEL_XOR_BIT_17				(1 << 9)
 
 /** 965 MCH register controlling DRAM channel configuration */
 #define C0DRB3			0x10206