Hi David, On 09/26/2016 02:26 AM, David Laight wrote: > From: Eric Nelson >> Sent: 24 September 2016 15:42 >> The FEC receive accelerator (RACC) supports shifting the data payload of >> received packets by 16-bits, which aligns the payload (IP header) on a >> 4-byte boundary, which is, if not required, at least strongly suggested >> by the Linux networking layer. > ... >> + /* align IP header */ >> + val |= FEC_RACC_SHIFT16; > > I can't help feeling that there needs to be corresponding > changes to increase the buffer size by 2 (maybe for large mtu) > and to discard two bytes from the frame length. >
In the normal case, the fec driver over-allocates all receive packets to be of size FEC_ENET_RX_FRSIZE (2048) minus the value of rx_align, which is either 0x0f (ARM) or 0x03 (PPC). If the frame length is less than rx_copybreak (typically 256), then the frame length from the receive buffer descriptor is used to control the allocation size for a copied buffer, and this will include the two bytes of padding if RACC_SHIFT16 is set. > If probably ought to be predicated on NET_IP_ALIGN as well. > Can you elaborate? Please advise, Eric