drm/i915: Restore the kernel context after verifying the w/a

As a safety net, flush the engine verifications and restore the kernel
context.

Closes: https://gitlab.freedesktop.org/drm/intel/issues/971Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200126194618.2131078-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gt/intel_gt.c

@@ -538,6 +538,10 @@ static int __engines_verify_workarounds(struct intel_gt *gt)
 			err = -EIO;
 	}
 
+	/* Flush and restore the kernel context for safety */
+	if (intel_gt_wait_for_idle(gt, I915_GEM_IDLE_TIMEOUT) == -ETIME)
+		err = -EIO;
+
 	return err;
 }