[PATCH v2 1/3] gianfar: Implement workaround for eTSEC74 erratum

[David Miller]

From: Anton Vorontsov <avorontsov at mvista.com>
Date: Wed, 30 Jun 2010 20:39:12 +0400

> MPC8313ECE says:
> 
> "If MACCFG2[Huge Frame]=0 and the Ethernet controller receives frames
>  which are larger than MAXFRM, the controller truncates the frames to
>  length MAXFRM and marks RxBD[TR]=1 to indicate the error. The controller
>  also erroneously marks RxBD[TR]=1 if the received frame length is MAXFRM
>  or MAXFRM-1, even though those frames are not truncated.
>  No truncation or truncation error occurs if MACCFG2[Huge Frame]=1."
> 
> There are two options to workaround the issue:
> 
> "1. Set MACCFG2[Huge Frame]=1, so no truncation occurs for invalid large
>  frames. Software can determine if a frame is larger than MAXFRM by
>  reading RxBD[LG] or RxBD[Data Length].
> 
>  2. Set MAXFRM to 1538 (0x602) instead of the default 1536 (0x600), so
>  normal-length frames are not marked as truncated. Software can examine
>  RxBD[Data Length] to determine if the frame was larger than MAXFRM-2."
> 
> This patch implements the first workaround option by setting HUGEFRAME
> bit, and gfar_clean_rx_ring() already checks the RxBD[Data Length].
> 
> Signed-off-by: Anton Vorontsov <avorontsov at mvista.com>

Applied.