[Intel-gfx] [PATCH] drm/i915: fix swizzle detection for gen3

[Daniel Vetter]

It looks like the desktop variants of i915 and i945 also have the DCC
register to control dram channel interleave and cpu side bit6
swizzling.

Unfortunately internal Cspec/ConfigDB documentation for these ancient chips
have already been dropped and there seem to be no archives. Also
somebody thought the swizzling behaviour is surely a worthy secret to
keep and redacted any mention of these fields from the published Intel
datasheets.

I suspect the hw engineers were really proud of the page coloring
they've achieved in their first dual channel dram controller with
bit17 - after all Bspec explains in great length the optimal layout of
page frame numbers modulo 4 for the color and depth buffers, too.
Later on when they've started to work on VT-d they shamefully
discoverd their stupidity and tried to cover the tracks ...

Tested-by: Daniel Vetter <daniel.vetter at ffwll.ch> (i915g)
Tested-by: Pavel Ondračka <pavel.ondracka at email.cz> (i945g)
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=42625
Cc: stable at kernel.org
Signed-Off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
---

v2: Spelling fix in the commit msg.

 drivers/gpu/drm/i915/i915_gem_tiling.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_tiling.c b/drivers/gpu/drm/i915/i915_gem_tiling.c
index 31d334d..861223b 100644
--- a/drivers/gpu/drm/i915/i915_gem_tiling.c
+++ b/drivers/gpu/drm/i915/i915_gem_tiling.c
@@ -107,10 +107,10 @@ i915_gem_detect_bit_6_swizzle(struct drm_device *dev)
 		 */
 		swizzle_x = I915_BIT_6_SWIZZLE_NONE;
 		swizzle_y = I915_BIT_6_SWIZZLE_NONE;
-	} else if (IS_MOBILE(dev)) {
+	} else if (IS_MOBILE(dev) || (IS_GEN3(dev) && !IS_G33(dev))) {
 		uint32_t dcc;
 
-		/* On mobile 9xx chipsets, channel interleave by the CPU is
+		/* On 9xx chipsets, channel interleave by the CPU is
 		 * determined by DCC.  For single-channel, neither the CPU
 		 * nor the GPU do swizzling.  For dual channel interleaved,
 		 * the GPU's interleave is bit 9 and 10 for X tiled, and bit
-- 
1.7.6.4