From be292e1563ac5bebc5d84c914a9e5019a0b2114f Mon Sep 17 00:00:00 2001 From: Damien Lespiau Date: Wed, 27 Aug 2014 13:24:51 +0200 Subject: [PATCH] drm/i915/bdw: Let the memory controller do all the swizzling Previously, it was possible for the GPU memory accesses to be swizzled to try to optimize the fetches for tiled buffers. This swizzling was on top of what the memory controller in the uncore already does. With broadwell, we drop that GPU side swizzling, and the corresponding initialization in 3 units (GAM, GT, DE). All those bits are reserved, as specs put it: Before Gen8, there was a historical configuration control field to swizzle address bit[6] for in X/Y tiling modes. This was set in three different places: TILECTL[1:0], ARB_MODE[5:4], and DISP_ARB_CTL[14:13]" For Gen8 the swizzle fields are all reserved, and the CPU's memory controller performs all address swizzling modifications. This also means that user space doesn't have to manually swizzle when accessing tiled buffers from the CPU, and so we always return I915_BIT_6_SWIZZLE_NONE from i915_gem_detect_bit_6_swizzle(), which short-circuits the initialization of the registers mentionned above in i915_gem_init_swizzling(). v2: Refine the explanation a bit more (Daniel) v3: Make it BDW+ specific (Steve) Cc: Steve Aarnio Signed-off-by: Damien Lespiau [danvet: Keep the actual code to set the tiling bits for now, in case some bios escaped to the wild that uses this - we'd need it for fastboot.] Signed-off-by: Daniel Vetter --- drivers/gpu/drm/i915/i915_gem_tiling.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/drivers/gpu/drm/i915/i915_gem_tiling.c b/drivers/gpu/drm/i915/i915_gem_tiling.c index 7e623bf097a1..2cefb597df6d 100644 --- a/drivers/gpu/drm/i915/i915_gem_tiling.c +++ b/drivers/gpu/drm/i915/i915_gem_tiling.c @@ -91,7 +91,14 @@ i915_gem_detect_bit_6_swizzle(struct drm_device *dev) uint32_t swizzle_x = I915_BIT_6_SWIZZLE_UNKNOWN; uint32_t swizzle_y = I915_BIT_6_SWIZZLE_UNKNOWN; - if (IS_VALLEYVIEW(dev)) { + if (INTEL_INFO(dev)->gen >= 8 || IS_VALLEYVIEW(dev)) { + /* + * On BDW+, swizzling is not used. We leave the CPU memory + * controller in charge of optimizing memory accesses without + * the extra address manipulation GPU side. + * + * VLV and CHV don't have GPU swizzling. + */ swizzle_x = I915_BIT_6_SWIZZLE_NONE; swizzle_y = I915_BIT_6_SWIZZLE_NONE; } else if (INTEL_INFO(dev)->gen >= 6) { -- 2.20.1