[PATCH 5/8] drm/i915/gt: Sanitize GPU during prepare-to-suspend

[Chris Wilson]

After calling intel_gt_suspend_prepare(), the driver starts to turn off
various subsystems, such as clearing the GGTT, before calling
intel_gt_suspend_late() to relinquish control over the GT. However, if
we still have internal GPU state active as we clear the GGTT, the GPU
may write back its internal state to the residual GGTT addresses that
are now pointing into scratch. Let's reset the GPU to clear that
internal state as soon we have idled the GPU in prepare-to-suspend.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/gt/intel_gt_pm.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_gt_pm.c b/drivers/gpu/drm/i915/gt/intel_gt_pm.c
index 0bd303d2823e..24f2cc0b1ca0 100644
--- a/drivers/gpu/drm/i915/gt/intel_gt_pm.c
+++ b/drivers/gpu/drm/i915/gt/intel_gt_pm.c
@@ -152,6 +152,9 @@ static void gt_sanitize(struct intel_gt *gt, bool force)
 	enum intel_engine_id id;
 	intel_wakeref_t wakeref;
 
+	if (is_mock_gt(gt))
+		return;
+
 	GT_TRACE(gt, "force:%s", yesno(force));
 
 	/* Use a raw wakeref to avoid calling intel_display_power_get early */
@@ -295,6 +298,9 @@ void intel_gt_suspend_prepare(struct intel_gt *gt)
 	wait_for_suspend(gt);
 
 	intel_uc_suspend(&gt->uc);
+
+	/* Flush all the contexts and internal state before turning off GGTT */
+	gt_sanitize(gt, false);
 }
 
 static suspend_state_t pm_suspend_target(void)
@@ -337,7 +343,7 @@ void intel_gt_suspend_late(struct intel_gt *gt)
 		intel_llc_disable(&gt->llc);
 	}
 
-	gt_sanitize(gt, false);
+	gt_sanitize(gt, false); /* Be paranoid, remove all residual GPU state */
 
 	GT_TRACE(gt, "\n");
 }
-- 
2.20.1