RE: pch_gbe: dont-copy-payload (was [PATCH 1/4] ...)

On Mon, 2012-08-06 at 07:19 -0700, Andy Cress wrote:

I found out why the proposed dont-copy-payload patch didn't work with
this pch_gbe NIC.
This NIC PHY requires 64-byte-aligned DMA, and the transmit buffers
won't be transferred if skb->data is not 64-byte-aligned.  Apparently
the data copy has a by-product of aligning the buffers.  

I tried using skb_reserve(skb,64) in pch_gbe_alloc_tx_buffers and
pch-gbe_alloc_rx_buffers, but that didn't seem to resolve it.

How can I make sure that the transmit data buffers are
64-byte-aligned?

There is no support for such requirement in linux stacks.

Only solution for the driver is to copy all frames to 64-byte-aligned
bounce buffers.