drm/i915: Fix incorrect assert about pending power domain async-put work

It's possible that an already dequeued put_async_work() will release the
reference (*) that was put asynchronously after the dequeue happened.
This leaves an async-put work pending, without any reference to release.
A subsequent async-put may trigger the

drm_WARN_ON(!queue_delayed_work(&power_domains->async_put_work));

warn due to async_put_work() still pending. To avoid the warn, cancel
the pending async_put_work() when releasing the reference at (*) above.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/3421
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/2289Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Anshuman Gupta <anshuman.gupta@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210526143729.2563672-2-imre.deak@intel.com

drivers/gpu/drm/i915/display/intel_display_power.c

@@ -2263,6 +2263,12 @@ intel_display_power_put_async_work(struct work_struct *work)
 			fetch_and_zero(&power_domains->async_put_domains[1]);
 		queue_async_put_domains_work(power_domains,
 					     fetch_and_zero(&new_work_wakeref));
+	} else {
+		/*
+		 * Cancel the work that got queued after this one got dequeued,
+		 * since here we released the corresponding async-put reference.
+		 */
+		cancel_delayed_work(&power_domains->async_put_work);
 	}
 
 out_verify: