[PATCH 1/1] drm/i915/gsc: Fix the Driver-FLR completion

[Alan Previn]

The Driver-FLR flow may inadvertently exit early before the full
completion of the re-init of the internal HW state if we only poll
GU_DEBUG Bit31 (polling for it to toggle from 0 -> 1). Instead
we need a two-step completion wait-for-completion flow that also
involves GU_CNTL. See the patch and new code comments for detail.
This is new direction from HW architecture folks.

Signed-off-by: Alan Previn <alan.previn.teres.alexis at intel.com>
Fixes: 5a44fcd73498 ("drm/i915/gsc: Do a driver-FLR on unload if GSC was loaded")
---
 drivers/gpu/drm/i915/intel_uncore.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
index 8dee9e62a73e..959869e2ff05 100644
--- a/drivers/gpu/drm/i915/intel_uncore.c
+++ b/drivers/gpu/drm/i915/intel_uncore.c
@@ -2748,6 +2748,12 @@ static void driver_initiated_flr(struct intel_uncore *uncore)
 	/* Trigger the actual Driver-FLR */
 	intel_uncore_rmw_fw(uncore, GU_CNTL, 0, DRIVERFLR);
 
+	/* Completion Step 1 - poll for 'CNTL-BIT31 = 0' wait for hw teardown to complete */
+	ret = intel_wait_for_register_fw(uncore, GU_CNTL,
+					 DRIVERFLR_STATUS, 0,
+					 flr_timeout_ms);
+
+	/* Completion: Step 2 - poll for 'DEBUG-BIT31 = 1' for hw/fw re-init to complete */
 	ret = intel_wait_for_register_fw(uncore, GU_DEBUG,
 					 DRIVERFLR_STATUS, DRIVERFLR_STATUS,
 					 flr_timeout_ms);
@@ -2756,6 +2762,7 @@ static void driver_initiated_flr(struct intel_uncore *uncore)
 		return;
 	}
 
+	/* Write 1 to clear GU_DEBUG's sticky completion status bit */
 	intel_uncore_write_fw(uncore, GU_DEBUG, DRIVERFLR_STATUS);
 }
 

base-commit: 0a0ee61784df01ac098a92bd43673ee30c629f13
-- 
2.39.0