drm/i915: Invariably invalidate before ctx switch

We have been setting the bit which was originally BIOS dependent since:
commit f05bb0c7b624252a5e768287e340e8e45df96e42
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Sun Jan 20 16:33:32 2013 +0000

    drm/i915: GFX_MODE Flush TLB Invalidate Mode must be '1' for scanline waits

Therefore, we do not need to try to figure it out dynamically and we can
just always invalidate the TLBs.

It's a partial revert of:
commit 12b0286f49947a6cdc9285032d918466a8c3f5f9
Author: Ben Widawsky <ben@bwidawsk.net>
Date:   Mon Jun 4 14:42:50 2012 -0700

    drm/i915: possibly invalidate TLB before context switch

The original commit attempted to only invalidate when necessary
(very much a relic from the old days). Now, we can just always invalidate.

I guess the old TODO still exists. Since we seem to have abandoned ILK
contexts however, there isn't much point in even remembering.

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem_context.c

@@ -596,7 +596,7 @@ mi_set_context(struct intel_ring_buffer *ring,
 	 * explicitly, so we rely on the value at ring init, stored in
 	 * itlb_before_ctx_switch.
 	 */
-	if (IS_GEN6(ring->dev) && ring->itlb_before_ctx_switch) {
+	if (IS_GEN6(ring->dev)) {
 		ret = ring->flush(ring, I915_GEM_GPU_DOMAINS, 0);
 		if (ret)
 			return ret;

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -612,13 +612,6 @@ static int init_render_ring(struct intel_ring_buffer *ring)
 		 */
 		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_EXPLICIT);
 	}
 
 	if (INTEL_INFO(dev)->gen >= 6)

drivers/gpu/drm/i915/intel_ringbuffer.h

@@ -152,10 +152,6 @@ struct  intel_ring_buffer {
 
 	wait_queue_head_t irq_queue;
 
-	/**
-	 * Do an explicit TLB flush before MI_SET_CONTEXT
-	 */
-	bool itlb_before_ctx_switch;
 	struct i915_hw_context *default_context;
 	struct i915_hw_context *last_context;