[Intel-gfx] [PATCH] drm/i915: Try harder to reset the gen8+ engines

[Chris Wilson]

If at first we don't succeed, try again.

Running the reset and recovery routines in a loop ends in a "reset
request timeout" with a mtbf of an hour on Braswell. This is eerily
similar to the unrecoverable reset condition that first prompted us to
use the reset-request mechanism in commit 7fd2d26921d1 ("drm/i915: Reset
request handling for gen8+"). Repeating the reset request makes the
failure much harder to reproduce (but there is no reason to believe that
it is more than mere paper over a timing or other issue).

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala at intel.com>
Cc: Arun Siluvery <arun.siluvery at linux.intel.com>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Cc: stable at vger.kernel.org
---
 drivers/gpu/drm/i915/intel_uncore.c | 24 +++++++++++++-----------
 1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
index e9f68cd56e32..1be8ced03ba5 100644
--- a/drivers/gpu/drm/i915/intel_uncore.c
+++ b/drivers/gpu/drm/i915/intel_uncore.c
@@ -1688,20 +1688,22 @@ int intel_wait_for_register(struct drm_i915_private *dev_priv,
 static int gen8_request_engine_reset(struct intel_engine_cs *engine)
 {
 	struct drm_i915_private *dev_priv = engine->i915;
-	int ret;
+	int loop = 3;
 
-	I915_WRITE_FW(RING_RESET_CTL(engine->mmio_base),
-		      _MASKED_BIT_ENABLE(RESET_CTL_REQUEST_RESET));
+	do {
+		I915_WRITE_FW(RING_RESET_CTL(engine->mmio_base),
+			      _MASKED_BIT_ENABLE(RESET_CTL_REQUEST_RESET));
 
-	ret = intel_wait_for_register_fw(dev_priv,
-					 RING_RESET_CTL(engine->mmio_base),
-					 RESET_CTL_READY_TO_RESET,
-					 RESET_CTL_READY_TO_RESET,
-					 700);
-	if (ret)
-		DRM_ERROR("%s: reset request timeout\n", engine->name);
+		if (!intel_wait_for_register_fw(dev_priv,
+						RING_RESET_CTL(engine->mmio_base),
+						RESET_CTL_READY_TO_RESET,
+						RESET_CTL_READY_TO_RESET,
+						700))
+			return 0;
+	} while (--loop);
 
-	return ret;
+	DRM_ERROR("%s: reset request timeout\n", engine->name);
+	return -EIO;
 }
 
 static void gen8_unrequest_engine_reset(struct intel_engine_cs *engine)
-- 
2.9.3