drm/i915: Respect GM965/GM45 bit-17-instead-of-bit-11 option for swiz…

…zling.

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