2014-07-22 9:27 GMT-07:00 Cyrille Pitchen <[email protected]>: > Le 18/07/2014 17:36, Eric Dumazet a écrit : >> On Fri, 2014-07-18 at 16:21 +0200, Cyrille Pitchen wrote: >>> Signed-off-by: Cyrille Pitchen <[email protected]> >>> --- >>> drivers/net/ethernet/cadence/macb.c | 29 ++++++++++++++++++++++++++++- >>> drivers/net/ethernet/cadence/macb.h | 2 ++ >>> 2 files changed, 30 insertions(+), 1 deletion(-) >>> >>> diff --git a/drivers/net/ethernet/cadence/macb.c >>> b/drivers/net/ethernet/cadence/macb.c >>> index 9bdcd1b..6acd6e2 100644 >>> --- a/drivers/net/ethernet/cadence/macb.c >>> +++ b/drivers/net/ethernet/cadence/macb.c >>> @@ -766,6 +766,8 @@ static int gem_rx(struct macb *bp, int budget) >>> >>> skb->protocol = eth_type_trans(skb, bp->dev); >>> skb_checksum_none_assert(skb); >>> + if (bp->dev->features & NETIF_F_RXCSUM) >>> + skb->ip_summed = CHECKSUM_UNNECESSARY; >>> >> >> >> Really ? >> >> If this is what you meant, this deserves a big and fat comment. >> >> >> > Hi Eric, > > Isn't it the proper way to do? According to Cadence documentation about RX > checksum offload: > "If any of the checksums (IP, TCP or UDP) are verified incorrect by the GEM, > the packet is discarded." > > If I understand, when RX checksum offload is enabled setting bit 24 of the > Network Configuration Register, the driver only receives RX frames with > correct checksum. Then it tells the kernel that there's no need to verify the > checksum again in software. This is done setting skb->ip_summed to > CHECKSUM_UNNECESSARY. Intel e1000 driver does the same in e1000_rx_checksum() > function.
This is not the same thing as what the e1000 driver is doing, the e1000 driver is checking a per-packet status mask which tells it whether a given packet had its protocol level checksum computed by the HW. I think there might be some slight confusion here between the Ethernet frame Frame Control Checksum which is at the Ethernet level, and will (with most adapters not supporting RX_FCS_ERR) cause the Ethernet controller to drop frames at the MAC level, and the higher level protocol checksums such as the TCP or UDP checksum. > > Also bit 24 of the Network Configuration Register is updated by macb_open() > and macb_set_features() so it always matches the state of NETIF_F_RXCSUM flag > in dev->features, once the network interface is up. That's why I'd rather > read from dev->features than read from register. I don't think the Cadence GEM Ethernet controller is any different than other hardware out there, there must be a per-packet status bit which tells whether the TCP/UDP or other protocol checksum was successfully validated by the hardware. One of the reason for that, is that depending on the type of traffic your receive (e.g: ARP), there might be no protocol-level checksum at all in the packet, and the hardware should know about that. > > Did I make a mistake? Is it the kind of comment you expect to be added? > > Regards, > > Cyrille > > _______________________________________________ > linux-arm-kernel mailing list > [email protected] > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel -- Florian -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
