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 Ondra?ka <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> --- 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 -- 1.7.7.3
