netdev - Re: bnx2 fails to compile on parisc because of missing get_dma

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Date:	Wed, 16 Jun 2010 20:53:57 -0700
From:	"Michael Chan" <mchan@...adcom.com>
To:	"'Mike Frysinger'" <vapier@...too.org>,
	"James Bottomley" <JBottomley@...ell.com>
cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-parisc@...r.kernel.org" <linux-parisc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"FUJITA Tomonori" <fujita.tomonori@....ntt.co.jp>
Subject: Re: bnx2 fails to compile on parisc because of missing
 get_dma_ops()

Mike Frysinger wrote:

> On Wed, Jun 16, 2010 at 9:13 PM, James Bottomley wrote:
> > I'm not quite sure whose fault this one is.
> >
> > However, this code in bnx2.c:
> >
> >                if (!get_dma_ops(&pdev->dev)->sync_single_for_cpu) {
> >                        next_rx_buf =
> >                                &rxr->rx_buf_ring[
> >                                        RX_RING_IDX(NEXT_RX_BD(sw_cons))];
> >                        prefetch(next_rx_buf->desc);
> >                }
> >
> > Looks remarkably fragile: what exactly is it trying to do?

If sync_single is not defined, that means the CPU has a consistent
view of next_rx_buf and so it makes sense to prefetch it.

> >
> > The commit that causes the problem:
> >
> > commit a33fa66bcf365ffe5b79d1ae1d3582cc261ae56e
> > Author: Michael Chan <mchan@...adcom.com>
> > Date:   Thu May 6 08:58:13 2010 +0000
> >
> >    bnx2: Add prefetches to rx path.
> >
> > Looks fairly innocuous by the description.
> >
> > Should parisc have a get_dma_ops()?  We don't need one
> because our dma
> > ops are per platform not per bus.
>
> looks like it'll be broken on more than just parisc:
> $ grep get_dma_ops arch/*/include/asm/ -rl | cut -d/ -f 2
> alpha
> ia64
> microblaze
> powerpc
> sh
> sparc
> x86

Most of these archs use the dma functions in:

<asm-genric/dma-mapping-common.h>

so it's not a problem.

I think I'll send in a patch to remove that part of the code
from bnx2.c for now.

Thanks.

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