[Intel-gfx] [PATCH] drm/i915: Stop ring before doing readiness check

[Mika Kuoppala]

Evidence indicates that even if the hardware happily
tells us to proceed with reset, it really isn't ready.
Resetting a freely running batchbuffer after we have
got ack for readiness, still can cause a system hang.

Attempt to stop ring before proceeding for ready check
and reset to avoid losing the machine.

Testcase: igt/prime_busy/hang-* # kbl
Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
Cc: Chris Wilson <chris at chris-wilson.co.uk>
Signed-off-by: Mika Kuoppala <mika.kuoppala at intel.com>
---
 drivers/gpu/drm/i915/intel_uncore.c | 54 ++++++++++++++++++++++---------------
 1 file changed, 32 insertions(+), 22 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
index 1b38eb94d461..f9ef1931516c 100644
--- a/drivers/gpu/drm/i915/intel_uncore.c
+++ b/drivers/gpu/drm/i915/intel_uncore.c
@@ -1361,33 +1361,38 @@ int i915_reg_read_ioctl(struct drm_device *dev,
 	return ret;
 }
 
+static void gen3_stop_ring(struct intel_engine_cs *engine)
+{
+	struct drm_i915_private *dev_priv = engine->i915;
+	const u32 base = engine->mmio_base;
+	const i915_reg_t mode = RING_MI_MODE(base);
+
+	I915_WRITE_FW(mode, _MASKED_BIT_ENABLE(STOP_RING));
+	if (intel_wait_for_register_fw(dev_priv,
+				       mode,
+				       MODE_IDLE,
+				       MODE_IDLE,
+				       500))
+		DRM_DEBUG_DRIVER("%s: timed out on STOP_RING\n",
+				 engine->name);
+
+	I915_WRITE_FW(RING_CTL(base), 0);
+	I915_WRITE_FW(RING_HEAD(base), 0);
+	I915_WRITE_FW(RING_TAIL(base), 0);
+
+	/* Check acts as a post */
+	if (I915_READ_FW(RING_HEAD(base)) != 0)
+		DRM_DEBUG_DRIVER("%s: ring head not parked\n",
+				 engine->name);
+}
+
 static void gen3_stop_rings(struct drm_i915_private *dev_priv)
 {
 	struct intel_engine_cs *engine;
 	enum intel_engine_id id;
 
-	for_each_engine(engine, dev_priv, id) {
-		const u32 base = engine->mmio_base;
-		const i915_reg_t mode = RING_MI_MODE(base);
-
-		I915_WRITE_FW(mode, _MASKED_BIT_ENABLE(STOP_RING));
-		if (intel_wait_for_register_fw(dev_priv,
-					       mode,
-					       MODE_IDLE,
-					       MODE_IDLE,
-					       500))
-			DRM_DEBUG_DRIVER("%s: timed out on STOP_RING\n",
-					 engine->name);
-
-		I915_WRITE_FW(RING_CTL(base), 0);
-		I915_WRITE_FW(RING_HEAD(base), 0);
-		I915_WRITE_FW(RING_TAIL(base), 0);
-
-		/* Check acts as a post */
-		if (I915_READ_FW(RING_HEAD(base)) != 0)
-			DRM_DEBUG_DRIVER("%s: ring head not parked\n",
-					 engine->name);
-	}
+	for_each_engine(engine, dev_priv, id)
+		gen3_stop_ring(engine);
 }
 
 static bool i915_reset_complete(struct pci_dev *pdev)
@@ -1668,6 +1673,11 @@ static int gen8_reset_engine_start(struct intel_engine_cs *engine)
 	struct drm_i915_private *dev_priv = engine->i915;
 	int ret;
 
+	/* If the bb is still running at this stage, forcing a
+	 * reset risks a system hang.
+	 */
+	gen3_stop_ring(engine);
+
 	I915_WRITE_FW(RING_RESET_CTL(engine->mmio_base),
 		      _MASKED_BIT_ENABLE(RESET_CTL_REQUEST_RESET));
 
-- 
2.11.0