[PATCH 82/82] drm/i915: Suppress switch_mm emission between the same aliasing_ppgtt

[Chris Wilson]

When switching between contexts using the aliasing_ppgtt, the VM is
shared. We don't need to reload the PD registers unless they are dirty.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_gem_context.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index f8f155c0e3f7..944ba7eeb62f 100644
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -678,10 +678,10 @@ static inline bool skip_rcs_switch(struct i915_hw_ppgtt *ppgtt,
 }
 
 static bool
-needs_pd_load_pre(struct i915_hw_ppgtt *ppgtt,
-		  struct intel_engine_cs *engine,
-		  struct i915_gem_context *to)
+needs_pd_load_pre(struct i915_hw_ppgtt *ppgtt, struct intel_engine_cs *engine)
 {
+	struct i915_hw_ppgtt *last_ppgtt;
+
 	if (!ppgtt)
 		return false;
 
@@ -690,7 +690,9 @@ needs_pd_load_pre(struct i915_hw_ppgtt *ppgtt,
 		return true;
 
 	/* Same context without new entries, skip */
-	if (engine->legacy_active_context == to &&
+	last_ppgtt =
+		engine->legacy_active_context->ppgtt ?: engine->i915->mm.aliasing_ppgtt;
+	if (last_ppgtt == ppgtt &&
 	    !(intel_engine_flag(engine) & ppgtt->pd_dirty_rings))
 		return false;
 
@@ -734,7 +736,7 @@ static int do_rcs_switch(struct drm_i915_gem_request *req)
 	if (skip_rcs_switch(ppgtt, engine, to))
 		return 0;
 
-	if (needs_pd_load_pre(ppgtt, engine, to)) {
+	if (needs_pd_load_pre(ppgtt, engine)) {
 		/* Older GENs and non render rings still want the load first,
 		 * "PP_DCLV followed by PP_DIR_BASE register through Load
 		 * Register Immediate commands in Ring Buffer before submitting
@@ -831,7 +833,7 @@ int i915_switch_context(struct drm_i915_gem_request *req)
 		struct i915_hw_ppgtt *ppgtt =
 			to->ppgtt ?: req->i915->mm.aliasing_ppgtt;
 
-		if (needs_pd_load_pre(ppgtt, engine, to)) {
+		if (needs_pd_load_pre(ppgtt, engine)) {
 			int ret;
 
 			trace_switch_mm(engine, to);
-- 
2.11.0