drm/i915/gt: Push engine stopping into reset-prepare

Push the engine stop into the back reset_prepare (where it already was!)
This allows us to avoid dangerously setting the RING registers to 0 for
logical contexts. If we clear the register on a live context, those
invalid register values are recorded in the logical context state and
replayed (with hilarious results).
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190716124931.5870-2-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gt/intel_lrc.c

@@ -2183,11 +2183,23 @@ static void execlists_reset_prepare(struct intel_engine_cs *engine)
 	__tasklet_disable_sync_once(&execlists->tasklet);
 	GEM_BUG_ON(!reset_in_progress(execlists));
 
-	intel_engine_stop_cs(engine);
-
 	/* And flush any current direct submission. */
 	spin_lock_irqsave(&engine->active.lock, flags);
 	spin_unlock_irqrestore(&engine->active.lock, flags);
+
+	/*
+	 * We stop engines, otherwise we might get failed reset and a
+	 * dead gpu (on elk). Also as modern gpu as kbl can suffer
+	 * from system hang if batchbuffer is progressing when
+	 * the reset is issued, regardless of READY_TO_RESET ack.
+	 * Thus assume it is best to stop engines on all gens
+	 * where we have a gpu reset.
+	 *
+	 * WaKBLVECSSemaphoreWaitPoll:kbl (on ALL_ENGINES)
+	 *
+	 * FIXME: Wa for more modern gens needs to be validated
+	 */
+	intel_engine_stop_cs(engine);
 }
 
 static void reset_csb_pointers(struct intel_engine_cs *engine)

drivers/gpu/drm/i915/gt/intel_reset.c

@@ -135,47 +135,6 @@ void __i915_request_reset(struct i915_request *rq, bool guilty)
 	}
 }
 
-static void gen3_stop_engine(struct intel_engine_cs *engine)
-{
-	struct intel_uncore *uncore = engine->uncore;
-	const u32 base = engine->mmio_base;
-
-	GEM_TRACE("%s\n", engine->name);
-
-	if (intel_engine_stop_cs(engine))
-		GEM_TRACE("%s: timed out on STOP_RING\n", engine->name);
-
-	intel_uncore_write_fw(uncore,
-			      RING_HEAD(base),
-			      intel_uncore_read_fw(uncore, RING_TAIL(base)));
-	intel_uncore_posting_read_fw(uncore, RING_HEAD(base)); /* paranoia */
-
-	intel_uncore_write_fw(uncore, RING_HEAD(base), 0);
-	intel_uncore_write_fw(uncore, RING_TAIL(base), 0);
-	intel_uncore_posting_read_fw(uncore, RING_TAIL(base));
-
-	/* The ring must be empty before it is disabled */
-	intel_uncore_write_fw(uncore, RING_CTL(base), 0);
-
-	/* Check acts as a post */
-	if (intel_uncore_read_fw(uncore, RING_HEAD(base)))
-		GEM_TRACE("%s: ring head [%x] not parked\n",
-			  engine->name,
-			  intel_uncore_read_fw(uncore, RING_HEAD(base)));
-}
-
-static void stop_engines(struct intel_gt *gt, intel_engine_mask_t engine_mask)
-{
-	struct intel_engine_cs *engine;
-	intel_engine_mask_t tmp;
-
-	if (INTEL_GEN(gt->i915) < 3)
-		return;
-
-	for_each_engine_masked(engine, gt->i915, engine_mask, tmp)
-		gen3_stop_engine(engine);
-}
-
 static bool i915_in_reset(struct pci_dev *pdev)
 {
 	u8 gdrst;
@@ -607,23 +566,6 @@ int __intel_gt_reset(struct intel_gt *gt, intel_engine_mask_t engine_mask)
 	 */
 	intel_uncore_forcewake_get(gt->uncore, FORCEWAKE_ALL);
 	for (retry = 0; ret == -ETIMEDOUT && retry < retries; retry++) {
-		/*
-		 * We stop engines, otherwise we might get failed reset and a
-		 * dead gpu (on elk). Also as modern gpu as kbl can suffer
-		 * from system hang if batchbuffer is progressing when
-		 * the reset is issued, regardless of READY_TO_RESET ack.
-		 * Thus assume it is best to stop engines on all gens
-		 * where we have a gpu reset.
-		 *
-		 * WaKBLVECSSemaphoreWaitPoll:kbl (on ALL_ENGINES)
-		 *
-		 * WaMediaResetMainRingCleanup:ctg,elk (presumably)
-		 *
-		 * FIXME: Wa for more modern gens needs to be validated
-		 */
-		if (retry)
-			stop_engines(gt, engine_mask);
-
 		GEM_TRACE("engine_mask=%x\n", engine_mask);
 		preempt_disable();
 		ret = reset(gt, engine_mask, retry);

drivers/gpu/drm/i915/gt/intel_ringbuffer.c

@@ -739,7 +739,45 @@ static int xcs_resume(struct intel_engine_cs *engine)
 
 static void reset_prepare(struct intel_engine_cs *engine)
 {
-	intel_engine_stop_cs(engine);
+	struct intel_uncore *uncore = engine->uncore;
+	const u32 base = engine->mmio_base;
+
+	/*
+	 * We stop engines, otherwise we might get failed reset and a
+	 * dead gpu (on elk). Also as modern gpu as kbl can suffer
+	 * from system hang if batchbuffer is progressing when
+	 * the reset is issued, regardless of READY_TO_RESET ack.
+	 * Thus assume it is best to stop engines on all gens
+	 * where we have a gpu reset.
+	 *
+	 * WaKBLVECSSemaphoreWaitPoll:kbl (on ALL_ENGINES)
+	 *
+	 * WaMediaResetMainRingCleanup:ctg,elk (presumably)
+	 *
+	 * FIXME: Wa for more modern gens needs to be validated
+	 */
+	GEM_TRACE("%s\n", engine->name);
+
+	if (intel_engine_stop_cs(engine))
+		GEM_TRACE("%s: timed out on STOP_RING\n", engine->name);
+
+	intel_uncore_write_fw(uncore,
+			      RING_HEAD(base),
+			      intel_uncore_read_fw(uncore, RING_TAIL(base)));
+	intel_uncore_posting_read_fw(uncore, RING_HEAD(base)); /* paranoia */
+
+	intel_uncore_write_fw(uncore, RING_HEAD(base), 0);
+	intel_uncore_write_fw(uncore, RING_TAIL(base), 0);
+	intel_uncore_posting_read_fw(uncore, RING_TAIL(base));
+
+	/* The ring must be empty before it is disabled */
+	intel_uncore_write_fw(uncore, RING_CTL(base), 0);
+
+	/* Check acts as a post */
+	if (intel_uncore_read_fw(uncore, RING_HEAD(base)))
+		GEM_TRACE("%s: ring head [%x] not parked\n",
+			  engine->name,
+			  intel_uncore_read_fw(uncore, RING_HEAD(base)));
 }
 
 static void reset_ring(struct intel_engine_cs *engine, bool stalled)