[PATCH] 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.

   v2: - Add error message for the teardown timeout (Anshuman)
       - Don't duplicate code in comments (Jani)
   v3: - Add get/put runtime-pm for this function. Though
         not functionally required during unload, its so the uncore
	 doesn't complain.

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 | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
index f018da7ebaac..9832b8ac8b1a 100644
--- a/drivers/gpu/drm/i915/intel_uncore.c
+++ b/drivers/gpu/drm/i915/intel_uncore.c
@@ -2724,10 +2724,13 @@ static void driver_initiated_flr(struct intel_uncore *uncore)
 {
 	struct drm_i915_private *i915 = uncore->i915;
 	const unsigned int flr_timeout_ms = 3000; /* specs recommend a 3s wait */
+	intel_wakeref_t wakeref;
 	int ret;
 
 	drm_dbg(&i915->drm, "Triggering Driver-FLR\n");
 
+	wakeref = intel_runtime_pm_get(&i915->runtime_pm);
+
 	/*
 	 * Make sure any pending FLR requests have cleared by waiting for the
 	 * FLR trigger bit to go to zero. Also clear GU_DEBUG's DRIVERFLR_STATUS
@@ -2742,22 +2745,36 @@ static void driver_initiated_flr(struct intel_uncore *uncore)
 		drm_err(&i915->drm,
 			"Failed to wait for Driver-FLR bit to clear! %d\n",
 			ret);
-		return;
+		goto out;
 	}
 	intel_uncore_write_fw(uncore, GU_DEBUG, DRIVERFLR_STATUS);
 
 	/* Trigger the actual Driver-FLR */
 	intel_uncore_rmw_fw(uncore, GU_CNTL, 0, DRIVERFLR);
 
+	/* Wait for hardware teardown to complete */
+	ret = intel_wait_for_register_fw(uncore, GU_CNTL,
+					 DRIVERFLR_STATUS, 0,
+					 flr_timeout_ms);
+	if (ret) {
+		drm_err(&i915->drm, "Driver-FLR-teardown wait completion failed! %d\n", ret);
+		goto out;
+	}
+
+	/* Wait for hardware/firmware re-init to complete */
 	ret = intel_wait_for_register_fw(uncore, GU_DEBUG,
 					 DRIVERFLR_STATUS, DRIVERFLR_STATUS,
 					 flr_timeout_ms);
 	if (ret) {
-		drm_err(&i915->drm, "wait for Driver-FLR completion failed! %d\n", ret);
-		return;
+		drm_err(&i915->drm, "Driver-FLR-reinit wait completion failed! %d\n", ret);
+		goto out;
 	}
 
+	/* Clear sticky completion status */
 	intel_uncore_write_fw(uncore, GU_DEBUG, DRIVERFLR_STATUS);
+
+out:
+	intel_runtime_pm_put(&i915->runtime_pm, wakeref);
 }
 
 /* Called via drm-managed action */
-- 
2.39.0