drm/xe/guc: Flush G2H handler when turning off CTs

Make sure G2H handler is not running when changing the CT state to drop
messages or disabled. This will help prevent races in the code ensuring
that G2H are not being processed after changing the state.

v2:
- s/flush_g2h_handler/stop_g2h_handler (Michal)
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
[Rodrigo remove the extra line while pushing]
Link: https://patchwork.freedesktop.org/patch/msgid/20240122210156.1517444-4-matthew.brost@intel.com

drivers/gpu/drm/xe/xe_guc_ct.c

@@ -346,26 +346,34 @@ int xe_guc_ct_enable(struct xe_guc_ct *ct)
 	return err;
 }
 
+static void stop_g2h_handler(struct xe_guc_ct *ct)
+{
+	cancel_work_sync(&ct->g2h_worker);
+}
+
 /**
  * xe_guc_ct_disable - Set GuC to disabled state
  * @ct: the &xe_guc_ct
  *
- * Set GuC CT to disabled state, no outstanding g2h expected in this transition
+ * Set GuC CT to disabled state and stop g2h handler. No outstanding g2h expected
+ * in this transition.
  */
 void xe_guc_ct_disable(struct xe_guc_ct *ct)
 {
 	xe_guc_ct_set_state(ct, XE_GUC_CT_STATE_DISABLED);
+	stop_g2h_handler(ct);
 }
 
 /**
  * xe_guc_ct_stop - Set GuC to stopped state
  * @ct: the &xe_guc_ct
  *
- * Set GuC CT to stopped state and clear any outstanding g2h
+ * Set GuC CT to stopped state, stop g2h handler, and clear any outstanding g2h
  */
 void xe_guc_ct_stop(struct xe_guc_ct *ct)
 {
 	xe_guc_ct_set_state(ct, XE_GUC_CT_STATE_STOPPED);
+	stop_g2h_handler(ct);
 }
 
 static bool h2g_has_room(struct xe_guc_ct *ct, u32 cmd_len)