[PATCH v2 2/3] gianfar: Implement workaround for eTSEC76 erratum
davem at davemloft.net
Thu Jul 1 04:37:19 EST 2010
From: Anton Vorontsov <avorontsov at mvista.com>
Date: Wed, 30 Jun 2010 20:39:13 +0400
> MPC8313ECE says:
> "For TOE=1 huge or jumbo frames, the data required to generate the
> checksum may exceed the 2500-byte threshold beyond which the controller
> constrains itself to one memory fetch every 256 eTSEC system clocks.
> This throttling threshold is supposed to trigger only when the
> controller has sufficient data to keep transmit active for the duration
> of the memory fetches. The state machine handling this threshold,
> however, fails to take large TOE frames into account. As a result,
> TOE=1 frames larger than 2500 bytes often see excess delays before start
> of transmission."
> This patch implements the workaround as suggested by the errata
> document, i.e.:
> "Limit TOE=1 frames to less than 2500 bytes to avoid excess delays due to
> memory throttling.
> When using packets larger than 2700 bytes, it is recommended to turn TOE
> To be sure, we limit the TOE frames to 2500 bytes, and do software
> checksumming instead.
> Signed-off-by: Anton Vorontsov <avorontsov at mvista.com>
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