dmaengine: bcm-sba-raid: Peek mbox when we have no free requests

When setting up RAID array on several NVMe disks we observed that
sba_alloc_request() start failing (due to no free requests left)
and RAID array setup becomes very slow.

To improve performance, we do mbox channel peek when we have
no free requests. This improves performance of RAID array setup
because mbox requests that were completed but not processed by
mbox completion worker will be processed immediately by mbox
channel peek.
Signed-off-by: Anup Patel <anup.patel@broadcom.com>
Reviewed-by: Ray Jui <ray.jui@broadcom.com>
Reviewed-by: Scott Branden <scott.branden@broadcom.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

drivers/dma/bcm-sba-raid.c

@@ -200,6 +200,14 @@ static inline u32 __pure sba_cmd_pq_c_mdata(u32 d, u32 b1, u32 b0)
 
 /* ====== General helper routines ===== */
 
+static void sba_peek_mchans(struct sba_device *sba)
+{
+	int mchan_idx;
+
+	for (mchan_idx = 0; mchan_idx < sba->mchans_count; mchan_idx++)
+		mbox_client_peek_data(sba->mchans[mchan_idx]);
+}
+
 static struct sba_request *sba_alloc_request(struct sba_device *sba)
 {
 	unsigned long flags;
@@ -211,8 +219,17 @@ static struct sba_request *sba_alloc_request(struct sba_device *sba)
 	if (req)
 		list_move_tail(&req->node, &sba->reqs_alloc_list);
 	spin_unlock_irqrestore(&sba->reqs_lock, flags);
-	if (!req)
+
+	if (!req) {
+		/*
+		 * We have no more free requests so, we peek
+		 * mailbox channels hoping few active requests
+		 * would have completed which will create more
+		 * room for new requests.
+		 */
+		sba_peek_mchans(sba);
 		return NULL;
+	}
 
 	req->flags = SBA_REQUEST_STATE_ALLOCED;
 	req->first = req;
@@ -560,17 +577,15 @@ static enum dma_status sba_tx_status(struct dma_chan *dchan,
 				     dma_cookie_t cookie,
 				     struct dma_tx_state *txstate)
 {
-	int mchan_idx;
 	enum dma_status ret;
 	struct sba_device *sba = to_sba_device(dchan);
 
-	for (mchan_idx = 0; mchan_idx < sba->mchans_count; mchan_idx++)
-		mbox_client_peek_data(sba->mchans[mchan_idx]);
-
 	ret = dma_cookie_status(dchan, cookie, txstate);
 	if (ret == DMA_COMPLETE)
 		return ret;
 
+	sba_peek_mchans(sba);
+
 	return dma_cookie_status(dchan, cookie, txstate);
 }