Re: [PATCH] sky2: Fix WARNING: at lib/dma-debug.c:902check_sync

From: Michael Chan
Date: Wed Jan 20 2010 - 15:22:40 EST

On Wed, 2010-01-20 at 10:03 -0800, Stephen Hemminger wrote:
> On Wed, 20 Jan 2010 09:41:03 +0000
> Jarek Poplawski <jarkao2@xxxxxxxxx> wrote:
> > > Seems like an underlying bug in the DMA api. Maybe it just can't
> > > handle operations on partial mapping.
> > >
> > > Other drivers with same problem:
> > > bnx2, cassini, pcnet32, r8169, rrunner, skge, sungem, tg3,
> >
> > It seems using the same length (even without pci_unmap_len()) is
> > crucial here, but I hope maintainers (added to CC) will take care.
> >

I'm still unsure how to do dma_sync properly in bnx2. In the current
code, we always dma_sync_for_cpu a small portion of the SKB because the
rx descriptor is at the beginning of the SKB. We get the packet length,
for example, from the rx descriptor.

If it's a big packet, we'll simply unmap the entire SKB buffer (with the
beginning portion already dma_sync'ed). If the packet is smaller than
what we dma_sync'ed, we'll just copy the data to a new SKB. We'll then
dma_sync_for_device the portion of the original buffer and recycle the
whole buffer back to the device for new packets.

So, is it correct to just change the dma_sync length to the full length
of the buffer? It doesn't sound right to me.


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