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SubjectRe: alpha iommu fixes
On Mon, May 21, 2001 at 12:05:20AM +1000, Andrew Morton wrote:
> Andrea Arcangeli wrote:
> >
> > [ cc'ed to l-k ]
> >
> > > DMA-mapping.txt assumes that it cannot fail.
> >
> > DMA-mapping.txt is wrong. Both pci_map_sg and pci_map_single failed if
> > they returned zero. You either have to drop the skb or to try again later
> > if they returns zero.
> >
>
> Well this is news to me. No drivers understand this.

Yes, almost all drivers are buggy.

> How long has this been the case? What platforms?

Always and all platforms.

Just think about this, you have 2^32 of bus address space, and you
theoritically can start I/O for more than 2^32 of phys memory, see?
Whatever platform it is it will never be able to guarantee all mappings
to succeed.

> For netdevices at least, the pci_map_single() call is always close
> to the site of the skb allocation. So what we can do is to roll
> them together and use the existing oom-handling associated with alloc_skb(),
> assuming the driver has it...

Fine.

Andrea
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