21.04.2010 23:52, Mike Frysinger wrote:
Wrong alignment in smc911x driver when reading a frame from fifo. Neither smc911x chip nor U-Boot doesn't use IP-alignment, so we don't need to add anything here.I know you use this driver a lot. Please comment on this patch.i really havent a clue what this change is doing, and the changelog doesnt make much sense to me. too many negatives perhaps ...
SMSC911x chips has alignment function to allow frame payload data (which comes after 14-bytes ethernet header) to be aligned at some boundary when reading it from fifo (usually - 4 bytes boundary). This is done by inserting fake zeros bytes BEFORE actual frame data when reading from SMSC's fifo. This function controlled by RX_CFG register. There are bits that represents amount of fake bytes to be inserted.
Linux uses alignment of 4 bytes. Ethernet frame header is 14 bytes long, so we need to add 2 fake bytes to get payload data aligned at 4-bytes boundary. Linux driver does this by adding IP_ALIGNMENT constant (defined at skb.h) when calculating fifo data length. But all network subsystem of Linux uses this constant too when calculating different offsets.
But u-boot does not use any packet data alignment, so we don't need to add anything when calculating fifo data length. Moreover, driver zeros the RX_CFG register just one line up, so chip does not insert any fake data. After calculating data length we always got 1 more word to read.
So, at almost every packet read we get an underflow condition at fifo and possible corruption of data. Especially at continuous transfers, such as tftp.
Just after removing this magic addition, I've got tftp transfer speed as it aught to be at 100Mbps. It was really slow before.
Sorry for my english, I'm just a bad russian boy %) -- WBR, Valentin CJSC "NII STT", Russia, Smolensk http://www.niistt.ru
smime.p7s
Description: S/MIME Cryptographic Signature
_______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
