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authorValentin Yakovenkov <yakovenkov@niistt.ru>2010-04-23 09:40:23 +0400
committerBen Warren <biggerbadderben@gmail.com>2010-05-03 14:52:49 -0700
commitbd75db3feb9a8e4123b76006dbe582b71adbf22f (patch)
treeb4007dcf9f70ee8c46439d854bd56f2bc03693a2 /common/cmd_portio.c
parentf0588fdf921c63f84051923bb29eb4255d62a6e7 (diff)
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smc911x driver frame alignment patch
SMSC911x chips have 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. 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 at the beginig. So calculated data length is always bigger by 1 word. It seems that 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. It seems that fifo underflow occurs only when using byte packing on 32-bit blackfin bus (may be because of very small delay between reads). Signed-off-by: Valentin Yakovenkov <yakovenkov@niistt.ru> Signed-off-by: Ben Warren <biggerbadderben@gmail.com>
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