MACE DMA problem on Powermac 7300

Risto Suominen risto.suominen at
Mon Dec 7 09:36:15 EST 2009

Hi, everybody,

I post this in hope that somebody could shed some light on how should
the DMA work in conjunction with the MACE ethernet controller. I find
difficult to understand why it does not work in my case:

What happens? First two bytes of a received frame are not what they
should be in more than 50% of frames. This can be avoided by receiving
the frame on a word boundary, but with the usual skb_reserve(..., 2)
(to make the IP header land on word boundary), it won't work.

So, I can make the driver work by receiving at 0 offset, and then
moving the data 2 bytes up, before handing it over to upper layers.

This used to work with a 2.4.27 kernel, obviously the Grand Central
DBDMA controller can receive on non-word boundaries. Now I have

Any ideas, what could cause this kind of behaviour (and regression)?

Best regards,
Risto Suominen

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