[Intel-gfx] [PATCH v2 2/2] drm/i915: Abandon the reset if we fail to stop the engines

[Chris Wilson]

Some machines, *cough* snb *cough*, fail catastrophically if asked to
reset the GPU under certain conditions. The initial guess is that this
is when the rings are still busy at the time of the reset request
(because that's a pattern we've seen elsewhere, hence why we do try
gen3_stop_engines() before reset) so abandon the reset and leave the
device wedged, if gen3_stop_engines() fails.

v2: Only give up if not idle after emptying the ring.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=103240
Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
---
 drivers/gpu/drm/i915/intel_uncore.c | 43 ++++++++++++++++++++++++++++---------
 1 file changed, 33 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
index 96ee6b2754be..f80dbff3595f 100644
--- a/drivers/gpu/drm/i915/intel_uncore.c
+++ b/drivers/gpu/drm/i915/intel_uncore.c
@@ -1372,7 +1372,7 @@ int i915_reg_read_ioctl(struct drm_device *dev,
 	return ret;
 }
 
-static void gen3_stop_engine(struct intel_engine_cs *engine)
+static bool gen3_stop_engine(struct intel_engine_cs *engine)
 {
 	struct drm_i915_private *dev_priv = engine->i915;
 	const u32 base = engine->mmio_base;
@@ -1392,26 +1392,46 @@ static void gen3_stop_engine(struct intel_engine_cs *engine)
 	I915_WRITE_FW(RING_HEAD(base), 0);
 	I915_WRITE_FW(RING_TAIL(base), 0);
 
+	/* Check acts as a post */
+	if (intel_wait_for_register_fw(dev_priv,
+				       mode,
+				       MODE_IDLE,
+				       MODE_IDLE,
+				       1000)) {
+		DRM_DEBUG_DRIVER("%s: timed out after clearing ring\n",
+				 engine->name);
+		return false;
+	}
+
 	/* The ring must be empty before it is disabled */
 	I915_WRITE_FW(RING_CTL(base), 0);
+	POSTING_READ_FW(RING_CTL(base));
 
-	/* Check acts as a post */
-	if (I915_READ_FW(RING_HEAD(base)) != 0)
-		DRM_DEBUG_DRIVER("%s: ring head not parked\n",
-				 engine->name);
+	return true;
 }
 
-static void i915_stop_engines(struct drm_i915_private *dev_priv,
-			      unsigned engine_mask)
+static int i915_stop_engines(struct drm_i915_private *dev_priv,
+			     unsigned engine_mask)
 {
 	struct intel_engine_cs *engine;
 	enum intel_engine_id id;
+	bool idle;
 
 	if (INTEL_GEN(dev_priv) < 3)
-		return;
+		return true;
 
+	idle = true;
 	for_each_engine_masked(engine, dev_priv, engine_mask, id)
-		gen3_stop_engine(engine);
+		idle &= gen3_stop_engine(engine);
+	if (idle)
+		return true;
+
+	dev_err(dev_priv->drm.dev, "Failed to stop all engines\n");
+	for_each_engine_masked(engine, dev_priv, engine_mask, id) {
+		struct drm_printer p = drm_debug_printer(__func__);
+		intel_engine_dump(engine, &p);
+	}
+	return false;
 }
 
 static bool i915_reset_complete(struct pci_dev *pdev)
@@ -1772,7 +1792,10 @@ int intel_gpu_reset(struct drm_i915_private *dev_priv, unsigned engine_mask)
 		 *
 		 * FIXME: Wa for more modern gens needs to be validated
 		 */
-		i915_stop_engines(dev_priv, engine_mask);
+		if (!i915_stop_engines(dev_priv, engine_mask)) {
+			ret = -EIO;
+			break;
+		}
 
 		ret = -ENODEV;
 		if (reset)
-- 
2.15.0.rc2