drm/xe: Use ordered WQ for G2H handler

System work queues are shared, use a dedicated work queue for G2H
processing to avoid G2H processing getting block behind system tasks.

Fixes: dd08ebf6c352 ("drm/xe: Introduce a new DRM driver for Intel GPUs")
Cc: <[e-mail]>
Signed-off-by: Matthew Brost <[e-mail]>
Reviewed-by: Francois Dugast <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/xe/xe_guc_ct.c

···
 {
 	struct xe_guc_ct *ct = arg;
 
+	destroy_workqueue(ct->g2h_wq);
 	xa_destroy(&ct->fence_lookup);
 }
 
···
 	int err;
 
 	xe_gt_assert(gt, !(guc_ct_size() % PAGE_SIZE));
+
+	ct->g2h_wq = alloc_ordered_workqueue("xe-g2h-wq", 0);
+	if (!ct->g2h_wq)
+		return -ENOMEM;
 
 	spin_lock_init(&ct->fast_lock);
 	xa_init(&ct->fence_lookup);

drivers/gpu/drm/xe/xe_guc_ct.h

···
 		return;
 
 	wake_up_all(&ct->wq);
-	queue_work(system_unbound_wq, &ct->g2h_worker);
+	queue_work(ct->g2h_wq, &ct->g2h_worker);
 	xe_guc_ct_fast_path(ct);
 }
 

drivers/gpu/drm/xe/xe_guc_ct_types.h

···
 	wait_queue_head_t wq;
 	/** @g2h_fence_wq: wait queue used for G2H fencing */
 	wait_queue_head_t g2h_fence_wq;
+	/** @g2h_wq: used to process G2H */
+	struct workqueue_struct *g2h_wq;
 	/** @msg: Message buffer */
 	u32 msg[GUC_CTB_MSG_MAX_LEN];
 	/** @fast_msg: Message buffer */