[PATCH 1/1] can: gs_usb: remove dma allocations

[Rhett Aultman <rhett.aultman@samsara.com>]

From: Vasanth Sadhasivan <vasanth.sadhasivan@samsara.com>

DMA allocated buffers are a precious resource. If there is no need for DMA
allocations, then it might be worth to use non-dma allocated buffers.
After testing the gs_usb driver with and without DMA allocation, there
does not seem to be a significant change in latency or cpu utilization
either way. Therefore, DMA allocation is not necessary and removed.

Co-developed-by: Rhett Aultman <rhett.aultman@samsara.com>
Signed-off-by: Rhett Aultman <rhett.aultman@samsara.com>
Signed-off-by: Vasanth Sadhasivan <vasanth.sadhasivan@samsara.com>
---
 drivers/net/can/usb/gs_usb.c | 38 ++++++++++--------------------------
 1 file changed, 10 insertions(+), 28 deletions(-)

diff --git a/drivers/net/can/usb/gs_usb.c b/drivers/net/can/usb/gs_usb.c
index baf749c8cda3..1bfc775c62c5 100644
--- a/drivers/net/can/usb/gs_usb.c
+++ b/drivers/net/can/usb/gs_usb.c
@@ -269,7 +269,6 @@ struct gs_can {
 	struct usb_anchor tx_submitted;
 	atomic_t active_tx_urbs;
 	void *rxbuf[GS_MAX_RX_URBS];
-	dma_addr_t rxbuf_dma[GS_MAX_RX_URBS];
 };
 
 /* usb interface struct */
@@ -587,9 +586,7 @@ static void gs_usb_xmit_callback(struct urb *urb)
 
 	if (urb->status)
 		netdev_info(netdev, "usb xmit fail %u\n", txc->echo_id);
-
-	usb_free_coherent(urb->dev, urb->transfer_buffer_length,
-			  urb->transfer_buffer, urb->transfer_dma);
+	devm_kfree(&urb->dev->dev, urb->transfer_buffer);
 }
 
 static netdev_tx_t gs_can_start_xmit(struct sk_buff *skb,
@@ -618,8 +615,7 @@ static netdev_tx_t gs_can_start_xmit(struct sk_buff *skb,
 	if (!urb)
 		goto nomem_urb;
 
-	hf = usb_alloc_coherent(dev->udev, dev->hf_size_tx, GFP_ATOMIC,
-				&urb->transfer_dma);
+	hf = devm_kmalloc(&dev->udev->dev, dev->hf_size_tx, GFP_ATOMIC);
 	if (!hf) {
 		netdev_err(netdev, "No memory left for USB buffer\n");
 		goto nomem_hf;
@@ -663,7 +659,6 @@ static netdev_tx_t gs_can_start_xmit(struct sk_buff *skb,
 			  hf, dev->hf_size_tx,
 			  gs_usb_xmit_callback, txc);
 
-	urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
 	usb_anchor_urb(urb, &dev->tx_submitted);
 
 	can_put_echo_skb(skb, netdev, idx, 0);
@@ -678,8 +673,7 @@ static netdev_tx_t gs_can_start_xmit(struct sk_buff *skb,
 		gs_free_tx_context(txc);
 
 		usb_unanchor_urb(urb);
-		usb_free_coherent(dev->udev, urb->transfer_buffer_length,
-				  urb->transfer_buffer, urb->transfer_dma);
+		devm_kfree(&dev->udev->dev, hf);
 
 		if (rc == -ENODEV) {
 			netif_device_detach(netdev);
@@ -699,8 +693,7 @@ static netdev_tx_t gs_can_start_xmit(struct sk_buff *skb,
 	return NETDEV_TX_OK;
 
  badidx:
-	usb_free_coherent(dev->udev, urb->transfer_buffer_length,
-			  urb->transfer_buffer, urb->transfer_dma);
+	devm_kfree(&dev->udev->dev, hf);
  nomem_hf:
 	usb_free_urb(urb);
 
@@ -744,7 +737,6 @@ static int gs_can_open(struct net_device *netdev)
 		for (i = 0; i < GS_MAX_RX_URBS; i++) {
 			struct urb *urb;
 			u8 *buf;
-			dma_addr_t buf_dma;
 
 			/* alloc rx urb */
 			urb = usb_alloc_urb(0, GFP_KERNEL);
@@ -752,10 +744,9 @@ static int gs_can_open(struct net_device *netdev)
 				return -ENOMEM;
 
 			/* alloc rx buffer */
-			buf = usb_alloc_coherent(dev->udev,
-						 dev->parent->hf_size_rx,
-						 GFP_KERNEL,
-						 &buf_dma);
+			buf = devm_kmalloc(&dev->udev->dev,
+					   dev->parent->hf_size_rx,
+					   GFP_KERNEL);
 			if (!buf) {
 				netdev_err(netdev,
 					   "No memory left for USB buffer\n");
@@ -763,8 +754,6 @@ static int gs_can_open(struct net_device *netdev)
 				return -ENOMEM;
 			}
 
-			urb->transfer_dma = buf_dma;
-
 			/* fill, anchor, and submit rx urb */
 			usb_fill_bulk_urb(urb,
 					  dev->udev,
@@ -773,7 +762,6 @@ static int gs_can_open(struct net_device *netdev)
 					  buf,
 					  dev->parent->hf_size_rx,
 					  gs_usb_receive_bulk_callback, parent);
-			urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
 
 			usb_anchor_urb(urb, &parent->rx_submitted);
 
@@ -786,16 +774,12 @@ static int gs_can_open(struct net_device *netdev)
 					   "usb_submit failed (err=%d)\n", rc);
 
 				usb_unanchor_urb(urb);
-				usb_free_coherent(dev->udev,
-						  sizeof(struct gs_host_frame),
-						  buf,
-						  buf_dma);
+				devm_kfree(&dev->udev->dev, buf);
 				usb_free_urb(urb);
 				break;
 			}
 
 			dev->rxbuf[i] = buf;
-			dev->rxbuf_dma[i] = buf_dma;
 
 			/* Drop reference,
 			 * USB core will take care of freeing it
@@ -863,10 +847,8 @@ static int gs_can_close(struct net_device *netdev)
 	if (!parent->active_channels) {
 		usb_kill_anchored_urbs(&parent->rx_submitted);
 		for (i = 0; i < GS_MAX_RX_URBS; i++)
-			usb_free_coherent(dev->udev,
-					  sizeof(struct gs_host_frame),
-					  dev->rxbuf[i],
-					  dev->rxbuf_dma[i]);
+			devm_kfree(&dev->udev->dev,
+				   dev->rxbuf[i]);
 	}
 
 	/* Stop sending URBs */
-- 
2.25.1