[PATCH v2] 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. 
Internal buffers used within urbs were managed and freed manually. These 
buffers are no longer needed to be managed by the driver. The 
URB_FREE_BUFFER flag, allows for the buffers in question to 
be automatically freed.

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 | 39 ++++++------------------------------
 1 file changed, 6 insertions(+), 33 deletions(-)

diff --git a/drivers/net/can/usb/gs_usb.c b/drivers/net/can/usb/gs_usb.c
index baf749c8cda3..8562553ea6d0 100644
--- a/drivers/net/can/usb/gs_usb.c
+++ b/drivers/net/can/usb/gs_usb.c
@@ -268,8 +268,6 @@ 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 +585,6 @@ 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);
 }
 
 static netdev_tx_t gs_can_start_xmit(struct sk_buff *skb,
@@ -618,8 +613,7 @@ 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 = kmalloc(dev->hf_size_tx, GFP_ATOMIC);
 	if (!hf) {
 		netdev_err(netdev, "No memory left for USB buffer\n");
 		goto nomem_hf;
@@ -663,7 +657,7 @@ 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;
+	urb->transfer_flags |= URB_FREE_BUFFER;
 	usb_anchor_urb(urb, &dev->tx_submitted);
 
 	can_put_echo_skb(skb, netdev, idx, 0);
@@ -678,8 +672,6 @@ 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);
 
 		if (rc == -ENODEV) {
 			netif_device_detach(netdev);
@@ -699,8 +691,7 @@ 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);
+	kfree(hf);
  nomem_hf:
 	usb_free_urb(urb);
 
@@ -744,7 +735,6 @@ 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 +742,8 @@ 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 = kmalloc(dev->parent->hf_size_rx,
+				      GFP_KERNEL);
 			if (!buf) {
 				netdev_err(netdev,
 					   "No memory left for USB buffer\n");
@@ -763,8 +751,6 @@ 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 +759,7 @@ 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;
+			urb->transfer_flags |= URB_FREE_BUFFER;
 
 			usb_anchor_urb(urb, &parent->rx_submitted);
 
@@ -786,17 +772,10 @@ 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);
 				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
 			 */
@@ -854,7 +833,6 @@ static int gs_can_close(struct net_device *netdev)
 	int rc;
 	struct gs_can *dev = netdev_priv(netdev);
 	struct gs_usb *parent = dev->parent;
-	unsigned int i;
 
 	netif_stop_queue(netdev);
 
@@ -862,11 +840,6 @@ static int gs_can_close(struct net_device *netdev)
 	parent->active_channels--;
 	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]);
 	}
 
 	/* Stop sending URBs */
-- 
2.25.1