drm/i915/gt: Call stop_ring() from ring resume, again

For reasons I cannot explain, except to say this is Sandybridge after
all, call stop_ring() again dring ring resume in order to prevent
mysterious hard hangs.

Testcase: igt/i915_selftest/hangcheck # snb
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Acked-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210121154950.19898-3-chris@chris-wilson.co.ukSigned-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

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

@@ -183,15 +183,36 @@ static void set_pp_dir(struct intel_engine_cs *engine)
 	}
 }
 
+static bool stop_ring(struct intel_engine_cs *engine)
+{
+	/* Empty the ring by skipping to the end */
+	ENGINE_WRITE_FW(engine, RING_HEAD, ENGINE_READ_FW(engine, RING_TAIL));
+	ENGINE_POSTING_READ(engine, RING_HEAD);
+
+	/* The ring must be empty before it is disabled */
+	ENGINE_WRITE_FW(engine, RING_CTL, 0);
+	ENGINE_POSTING_READ(engine, RING_CTL);
+
+	/* Then reset the disabled ring */
+	ENGINE_WRITE_FW(engine, RING_HEAD, 0);
+	ENGINE_WRITE_FW(engine, RING_TAIL, 0);
+
+	return (ENGINE_READ_FW(engine, RING_HEAD) & HEAD_ADDR) == 0;
+}
+
 static int xcs_resume(struct intel_engine_cs *engine)
 {
-	struct drm_i915_private *dev_priv = engine->i915;
 	struct intel_ring *ring = engine->legacy.ring;
 
 	ENGINE_TRACE(engine, "ring:{HEAD:%04x, TAIL:%04x}\n",
 		     ring->head, ring->tail);
 
-	if (HWS_NEEDS_PHYSICAL(dev_priv))
+	/* Double check the ring is empty & disabled before we resume */
+	synchronize_hardirq(engine->i915->drm.irq);
+	if (!stop_ring(engine))
+		goto err;
+
+	if (HWS_NEEDS_PHYSICAL(engine->i915))
 		ring_setup_phys_status_page(engine);
 	else
 		ring_setup_status_page(engine);
@@ -228,21 +249,10 @@ static int xcs_resume(struct intel_engine_cs *engine)
 	if (__intel_wait_for_register_fw(engine->uncore,
 					 RING_CTL(engine->mmio_base),
 					 RING_VALID, RING_VALID,
-					 5000, 0, NULL)) {
-		drm_err(&dev_priv->drm,
-			"%s initialization failed; "
-			"ctl %08x (valid? %d) head %08x [%08x] tail %08x [%08x] start %08x [expected %08x]\n",
-			engine->name,
-			ENGINE_READ(engine, RING_CTL),
-			ENGINE_READ(engine, RING_CTL) & RING_VALID,
-			ENGINE_READ(engine, RING_HEAD), ring->head,
-			ENGINE_READ(engine, RING_TAIL), ring->tail,
-			ENGINE_READ(engine, RING_START),
-			i915_ggtt_offset(ring->vma));
-		return -EIO;
-	}
+					 5000, 0, NULL))
+		goto err;
 
-	if (INTEL_GEN(dev_priv) > 2)
+	if (INTEL_GEN(engine->i915) > 2)
 		ENGINE_WRITE_FW(engine,
 				RING_MI_MODE, _MASKED_BIT_DISABLE(STOP_RING));
 
@@ -255,6 +265,19 @@ static int xcs_resume(struct intel_engine_cs *engine)
 	/* Papering over lost _interrupts_ immediately following the restart */
 	intel_engine_signal_breadcrumbs(engine);
 	return 0;
+
+err:
+	drm_err(&engine->i915->drm,
+		"%s initialization failed; "
+		"ctl %08x (valid? %d) head %08x [%08x] tail %08x [%08x] start %08x [expected %08x]\n",
+		engine->name,
+		ENGINE_READ(engine, RING_CTL),
+		ENGINE_READ(engine, RING_CTL) & RING_VALID,
+		ENGINE_READ(engine, RING_HEAD), ring->head,
+		ENGINE_READ(engine, RING_TAIL), ring->tail,
+		ENGINE_READ(engine, RING_START),
+		i915_ggtt_offset(ring->vma));
+	return -EIO;
 }
 
 static void sanitize_hwsp(struct intel_engine_cs *engine)
@@ -290,23 +313,6 @@ static void xcs_sanitize(struct intel_engine_cs *engine)
 	clflush_cache_range(engine->status_page.addr, PAGE_SIZE);
 }
 
-static bool stop_ring(struct intel_engine_cs *engine)
-{
-	/* Empty the ring by skipping to the end */
-	ENGINE_WRITE_FW(engine, RING_HEAD, ENGINE_READ_FW(engine, RING_TAIL));
-	ENGINE_POSTING_READ(engine, RING_HEAD);
-
-	/* The ring must be empty before it is disabled */
-	ENGINE_WRITE_FW(engine, RING_CTL, 0);
-	ENGINE_POSTING_READ(engine, RING_CTL);
-
-	/* Then reset the disabled ring */
-	ENGINE_WRITE_FW(engine, RING_HEAD, 0);
-	ENGINE_WRITE_FW(engine, RING_TAIL, 0);
-
-	return (ENGINE_READ_FW(engine, RING_HEAD) & HEAD_ADDR) == 0;
-}
-
 static void reset_prepare(struct intel_engine_cs *engine)
 {
 	/*
@@ -329,25 +335,23 @@ static void reset_prepare(struct intel_engine_cs *engine)
 
 	if (!stop_ring(engine)) {
 		/* G45 ring initialization often fails to reset head to zero */
-		drm_dbg(&engine->i915->drm,
-			"%s head not reset to zero "
-			"ctl %08x head %08x tail %08x start %08x\n",
-			engine->name,
-			ENGINE_READ_FW(engine, RING_CTL),
-			ENGINE_READ_FW(engine, RING_HEAD),
-			ENGINE_READ_FW(engine, RING_TAIL),
-			ENGINE_READ_FW(engine, RING_START));
-	}
-
-	if (!stop_ring(engine)) {
-		drm_err(&engine->i915->drm,
-			"failed to set %s head to zero "
-			"ctl %08x head %08x tail %08x start %08x\n",
-			engine->name,
-			ENGINE_READ_FW(engine, RING_CTL),
-			ENGINE_READ_FW(engine, RING_HEAD),
-			ENGINE_READ_FW(engine, RING_TAIL),
-			ENGINE_READ_FW(engine, RING_START));
+		ENGINE_TRACE(engine,
+			     "HEAD not reset to zero, "
+			     "{ CTL:%08x, HEAD:%08x, TAIL:%08x, START:%08x }\n",
+			     ENGINE_READ_FW(engine, RING_CTL),
+			     ENGINE_READ_FW(engine, RING_HEAD),
+			     ENGINE_READ_FW(engine, RING_TAIL),
+			     ENGINE_READ_FW(engine, RING_START));
+		if (!stop_ring(engine)) {
+			drm_err(&engine->i915->drm,
+				"failed to set %s head to zero "
+				"ctl %08x head %08x tail %08x start %08x\n",
+				engine->name,
+				ENGINE_READ_FW(engine, RING_CTL),
+				ENGINE_READ_FW(engine, RING_HEAD),
+				ENGINE_READ_FW(engine, RING_TAIL),
+				ENGINE_READ_FW(engine, RING_START));
+		}
 	}
 }