netdev - Re: [PATCH v4] FEC - fast ethernet controller for mpc52xx

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Message-ID: <20071025202908.GA2102@xyzzy.farnsworth.org>
Date:	Thu, 25 Oct 2007 13:29:08 -0700
From:	"Dale Farnsworth" <dale@...nsworth.org>
To:	Domen Puncer <domen.puncer@...argo.com>
Cc:	netdev@...r.kernel.org, linuxppc-dev@...abs.org
Subject: Re: [PATCH v4] FEC - fast ethernet controller for mpc52xx

On Thu, Oct 25, 2007 at 09:41:14PM +0200, Domen Puncer wrote:
> On 25/10/07 11:57 -0700, Dale Farnsworth wrote:
> > Domen wrote:
> > > > use your platform's dma mapping functions, rather than virt_to_phys()
> > > > 
> > > > it might be the exact same implementation, inside the platform 
> > > > internals, but drivers should not be using this directly.
> > > 
> > > I've replaced this with dma_map_single(), unmatched with
> > > dma_unmap_single(), since bestcomm doesn't have a way to do that
> > > and it's blank on ppc32 anyway.
> > > 
> > > Is this OK? PPC guys?
> > 
> > Even though dma_unmap_single() may be a no-op, calls to
> > dma_map_single() must be matched with calls to dma_unmap_single().
> > 
> > Perhaps with the additions below:
> > 
> > > +static void mpc52xx_fec_free_rx_buffers(struct bcom_task *s)
> > > +{
> > > +	struct sk_buff *skb;
> > > +
> > > +	while (!bcom_queue_empty(s)) {
> > > +		skb = bcom_retrieve_buffer(s, NULL, NULL);
> > 
> > 		dma_unmap_single(&skb->dev->dev, skb-data,
> > 				 FEC_RX_BUFFER_SIZE, DMA_FROM_DEVICE);
> 
> It looks to me like dma_unmap_single takes the mapped address
> (what dma_map_single returned), and not the address we're mapping
> (skb->data).

Yeah.  Sorry.  That won't be so easy.  We'll either need to
squirrel away the mapped address, or change the interface to
bcom_retrieve_buffers() so we can get the address.

IMO, it's still a requirement that we call dma_unmap_single() for
each call to dma_map_single().

-Dale
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