• C
    gianfar: Add FCS to rx buffer size (fix) · f5b720b8
    Claudiu Manoil 提交于
    For each Rx frame the eTSEC writes its FCS (Frame Check Sequence)
    to the Rx buffer.
    
    The eTSEC h/w manual states in the "Receive Buffer Descriptor Field
    Descriptions" table:
    "Data length is the number of octets written by the eTSEC into this BD's
    data buffer if L is cleared (the value is equal to MRBLR), or, if L is
    set, the length of the frame including *CRC*, FCB (if RCTRL[PRSDEP > 00),
    preamble (if MACCFG2[PreAmRxEn]=1), time stamp (if RCTRL[TS] = 1) and
    any padding (RCTRL[PAL])."
    
    Though the FCS bytes are removed by the driver before passing the skb
    to the net stack, the Rx buffer size computation does not currently
    take into account the FCS bytes (4 bytes).
    Because the Rx buffer size is multiple of 512 bytes, leaving out the
    FCS is not a problem for the default MTU of 1500, as the Rx buffer size
    is 1536 in this case.  However, for custom MTUs, where the difference
    between the MTU size and the Rx buffer size is less, this can be a
    problem as the computed Rx buffer size won't be enough to accomodate
    the FCS for a received frame that is big enough (close to MTU size).
    In such case the received frame is considered to be incomplete (L flag
    not set in the RxBD status) and silently dropped.
    
    Note that the driver does not currently support S/G on Rx, so it has to
    compute its Rx buffer size based on the MTU of the device.
    Reported-by: NKristian Otnes <kotnes@cisco.com>
    Signed-off-by: NClaudiu Manoil <claudiu.manoil@freescale.com>
    Signed-off-by: NDavid S. Miller <davem@davemloft.net>
    f5b720b8
gianfar.c 89.9 KB