Re: [parisc-linux] tulip DMA mapping

[Richard Hirst <rhirst@linuxcare.com>]

I've quoted the whole of Grants message below, so you can see the
context.  It looks like tulip is treating zero as meaning it
doesn't have anything to pci_unmap...

Grant Grundler wrote:
> Hi all,
> I see a "bug" in tulip's usage of mapping services.
> It's not the bug I was looking for unfortunately.
> 
> In line 217 of drivers/net/tulip/interrupt.c:
> 
>         if (tp->tx_buffers[entry].mapping)
>                 pci_unmap_single(tp->pdev,
>                                 tp->tx_buffers[entry].mapping,
>                                 sizeof(tp->setup_frame),
>                                 PCI_DMA_TODEVICE);
> 
> 0 is a valid pci_map_single() return value when the system has an IO MMU.
> 
> The system will panic before pci_map_single() will fail.
> The driver needs to remember some other way if a buffer was mapped or not.
> Or the Documentation/DMA-mapping.txt should be changed - ie add this
> to the interface definition and I can reserve the 1st mapping
> entry so no-one uses it.

Richard


On Fri, Nov 10, 2000 at 02:16:11AM -0800, David S. Miller wrote:
>    Date: Fri, 10 Nov 2000 10:18:08 +0000
>    From: Matthew Wilcox <matthew@wil.cx>
> 
>    > Should I be mailing Jeff Garzik <jgarzik@mandrakesoft.com> directly?
>    > Or can someone who knows Jeff point this out to him?
> 
>    i've cc'd jeff & dave miller on this.
> 
> In 2.4.x there is _NO_ error return from the PCI dma functions except
> the consistent DMA mapping ones.
> 
> This was an explicit design decision, the dynamic mapping functions
> should never fail, and if they do it is a hard error.
> 
> Therefore no drivers need to check for failure, as far as they are
> concerned, there is no failure.
> 
> So what is the issue?  In 2.5.x I'll add an error return facility
> (BTW: -1 ie. 0xfffffff would probably work as an error value on all
>  platforms :-)
> 
> Later,
> David S. Miller
> davem@redhat.com
> 
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