drm/i915: Remove redundant TLB invalidate on switching contexts

We are required to reload the TLBs around context switches
(MI_SET_CONTEXT specifically) and the recommendation is do that before
the MI_SET_CONTEXT so that it is serialised with the switch and not
forgotten:

[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 pipeline PIPE_CONTROL with TLB inv bit set
immediately before MI_SET_CONTEXT.

However, we already do an unconditional TLB invalidate before every
batch so this condition is satifisfied.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170227135913.8056-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gem_context.c

@@ -607,17 +607,6 @@ mi_set_context(struct drm_i915_gem_request *req, u32 hw_flags)
 		0;
 	int len;
 
-	/* w/a: If Flush TLB Invalidation Mode is enabled, driver must do a TLB
-	 * invalidation prior to MI_SET_CONTEXT. On GEN6 we don't set the value
-	 * explicitly, so we rely on the value at ring init, stored in
-	 * itlb_before_ctx_switch.
-	 */
-	if (IS_GEN6(dev_priv)) {
-		int ret = engine->emit_flush(req, EMIT_INVALIDATE);
-		if (ret)
-			return ret;
-	}
-
 	/* These flags are for resource streamer on HSW+ */
 	if (IS_HASWELL(dev_priv) || INTEL_GEN(dev_priv) >= 8)
 		flags |= (HSW_MI_RS_SAVE_STATE_EN | HSW_MI_RS_RESTORE_STATE_EN);