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

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Message-ID: <20071025165003.7972a0b6@freepuppy.rosehill>
Date:	Thu, 25 Oct 2007 16:50:03 -0700
From:	Stephen Hemminger <shemminger@...ux-foundation.org>
To:	"Dale Farnsworth" <dale@...nsworth.org>
Cc:	Domen Puncer <domen.puncer@...argo.com>, netdev@...r.kernel.org,
	linuxppc-dev@...abs.org
Subject: Re: [PATCH v4] FEC - fast ethernet controller for mpc52xx

On Thu, 25 Oct 2007 13:29:08 -0700
"Dale Farnsworth" <dale@...nsworth.org> wrote:

> 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().
> 

There exist some macro's for pci stuff to handle the nop case well
see: pci_unmap_addr(), pci_unmap_len().

-- 
Stephen Hemminger <shemminger@...ux-foundation.org>
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