drm/i915: Use Write-Through cacheing for the display plane on Iris
Haswell GT3e has the unique feature of supporting Write-Through cacheing
of objects within the eLLC/LLC. The purpose of this is to enable the display
plane to remain coherent whilst objects lie resident in the eLLC/LLC - so
that we, in theory, get the best of both worlds, perfect display and fast
access.
However, we still need to be careful as the CPU does not see the WT when
accessing the cache. In particular, this means that we need to flush the
cache lines after writing to an object through the CPU, and on
transitioning from a cached state to WT.
v2: Actually do the clflush on transition to WT, nagging by Ville.
v3: Flush the CPU cache after writes into WT objects.
v4: Rease onto LLC updates and report WT as "uncached" for
get_cache_level_ioctl to remain symmetric with set_cache_level_ioctl.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 1af59d7..6d07467 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -454,6 +454,7 @@
caches, eg sampler/render caches, and the
large Last-Level-Cache. LLC is coherent with
the CPU, but L3 is only visible to the GPU. */
+ I915_CACHE_WT, /* hsw:gt3e WriteThrough for scanouts */
};
typedef uint32_t gen6_gtt_pte_t;
@@ -1385,7 +1386,7 @@
unsigned int pending_fenced_gpu_access:1;
unsigned int fenced_gpu_access:1;
- unsigned int cache_level:2;
+ unsigned int cache_level:3;
unsigned int has_aliasing_ppgtt_mapping:1;
unsigned int has_global_gtt_mapping:1;
@@ -1530,6 +1531,7 @@
#define HAS_BLT(dev) (INTEL_INFO(dev)->has_blt_ring)
#define HAS_VEBOX(dev) (INTEL_INFO(dev)->has_vebox_ring)
#define HAS_LLC(dev) (INTEL_INFO(dev)->has_llc)
+#define HAS_WT(dev) (IS_HASWELL(dev) && to_i915(dev)->ellc_size)
#define I915_NEED_GFX_HWS(dev) (INTEL_INFO(dev)->need_gfx_hws)
#define HAS_HW_CONTEXTS(dev) (INTEL_INFO(dev)->gen >= 6)