From cc11763b3510e4942bfece052ccf329a7b086a32 Mon Sep 17 00:00:00 2001 From: Ben Hutchings Date: Wed, 26 Aug 2009 08:17:59 +0000 Subject: [PATCH] sfc: Work around XMAC bug causing packet loss with some peers Received frames must be re-clocked by the local XGXS to the 156.25 MHz (DDR) clock of the XGMII. If the remote clock is slightly faster this can reduce a minimum IPG of 64 bit-times (1 cycle) to 32 bit-times (half a cycle). If the XMAC detects that a frame has reached the maximum RX frame length in the same cycle that it receives one of these reduced IPGs, it may miss the IPG, causing two valid frames to be treated as a single invalid frame (over-length with bad CRC). We work around this by increasing the maximum RX frame length so that peers with matched MTU will not provoke this bug. Signed-off-by: Ben Hutchings Signed-off-by: David S. Miller --- drivers/net/sfc/net_driver.h | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/drivers/net/sfc/net_driver.h b/drivers/net/sfc/net_driver.h index 5eabede9ac18..298566da638b 100644 --- a/drivers/net/sfc/net_driver.h +++ b/drivers/net/sfc/net_driver.h @@ -984,9 +984,14 @@ static inline void clear_bit_le(unsigned nr, unsigned char *addr) * * The 10G MAC used in Falcon requires 8-byte alignment on the frame * length, so we round up to the nearest 8. + * + * Re-clocking by the XGXS on RX can reduce an IPG to 32 bits (half an + * XGMII cycle). If the frame length reaches the maximum value in the + * same cycle, the XMAC can miss the IPG altogether. We work around + * this by adding a further 16 bytes. */ #define EFX_MAX_FRAME_LEN(mtu) \ - ((((mtu) + ETH_HLEN + VLAN_HLEN + 4/* FCS */) + 7) & ~7) + ((((mtu) + ETH_HLEN + VLAN_HLEN + 4/* FCS */ + 7) & ~7) + 16) #endif /* EFX_NET_DRIVER_H */