USBNET: ax88179_178a: enable tso if usb host supports sg dma

This patch enables 'can_dma_sg' flag for ax88179_178a device
if the attached host controller supports building packet from
discontinuous buffers(DMA SG is possible), so TSO can be enabled
and skb fragment buffers can be passed to usb stack via urb->sg
directly.

With the patch, system CPU utilization decreased ~50% and throughput
increased by ~10% when doing iperf client test on one ARM A15 dual
core board.

Cc: Ben Hutchings <bhutchings@solarflare.com>
Cc: Grant Grundler <grundler@google.com>
Cc: Oliver Neukum <oneukum@suse.de>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Freddy Xin <freddy@asix.com.tw>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Acked-by: Eric Dumazet <edumazet@gmail.com>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/net/usb/ax88179_178a.c b/drivers/net/usb/ax88179_178a.c
index 2bc87e3a8141d259502bcfbfccc9e0a5b649800b..4233c05a3e326401ef1c2462d408861c693f0db1 100644 (file)
--- a/drivers/net/usb/ax88179_178a.c
+++ b/drivers/net/usb/ax88179_178a.c
@@ -1028,12 +1028,20 @@ static int ax88179_bind(struct usbnet *dev, struct usb_interface *intf)
        dev->mii.phy_id = 0x03;
        dev->mii.supports_gmii = 1;
 
+       if (usb_device_no_sg_constraint(dev->udev))
+               dev->can_dma_sg = 1;
+
        dev->net->features |= NETIF_F_IP_CSUM | NETIF_F_IPV6_CSUM |
                              NETIF_F_RXCSUM;
 
        dev->net->hw_features |= NETIF_F_IP_CSUM | NETIF_F_IPV6_CSUM |
                                 NETIF_F_RXCSUM;
 
+       if (dev->can_dma_sg) {
+               dev->net->features |= NETIF_F_SG | NETIF_F_TSO;
+               dev->net->hw_features |= NETIF_F_SG | NETIF_F_TSO;
+       }
+
        /* Enable checksum offload */
        *tmp = AX_RXCOE_IP | AX_RXCOE_TCP | AX_RXCOE_UDP |
               AX_RXCOE_TCPV6 | AX_RXCOE_UDPV6;