drm/i915: possibly invalidate TLB before context switch
From http://intellinuxgraphics.org/documentation/SNB/IHD_OS_Vol1_Part3.pdf
[DevSNB] If Flush TLB invalidation Mode is enabled it's the driver's
responsibility to invalidate the TLBs at least once after the previous
context switch after any GTT mappings changed (including new GTT
entries). This can be done by a pipelined PIPE_CONTROL with TLB inv bit
set immediately before MI_SET_CONTEXT.
On GEN7 the invalidation mode is explicitly set, but this appears to be
lacking for GEN6. Since I don't know the history on this, I've decided
to dynamically read the value at ring init time, and use that value
throughout.
v2: better comment (daniel)
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
diff --git a/drivers/gpu/drm/i915/intel_ringbuffer.c b/drivers/gpu/drm/i915/intel_ringbuffer.c
index a041492..7a16f16 100644
--- a/drivers/gpu/drm/i915/intel_ringbuffer.c
+++ b/drivers/gpu/drm/i915/intel_ringbuffer.c
@@ -423,6 +423,13 @@
*/
I915_WRITE(CACHE_MODE_0,
_MASKED_BIT_DISABLE(CM0_STC_EVICT_DISABLE_LRA_SNB));
+
+ /* This is not explicitly set for GEN6, so read the register.
+ * see intel_ring_mi_set_context() for why we care.
+ * TODO: consider explicitly setting the bit for GEN5
+ */
+ ring->itlb_before_ctx_switch =
+ !!(I915_READ(GFX_MODE) & GFX_TLB_INVALIDATE_ALWAYS);
}
if (INTEL_INFO(dev)->gen >= 6)