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    SubjectRe: [PATCH RFC] x86: Fix 64-bit DMA masks on VIA
    On Thursday 24 April 2008 16:32:40 Alan Cox wrote:
    > On Thu, 24 Apr 2008 16:06:00 +0200
    > Michael Buesch <> wrote:
    > > On Thursday 24 April 2008 15:43:50 Andi Kleen wrote:
    > > > Michael Buesch <> writes:
    > > >
    > > > > This untested patch is supposed to fix DMAing on some VIA boards.
    > > > > Currently the DMA subsystem returns an error, if the driver does
    > > > > tell that it supports a 64bit DMA mask. So the driver probing
    > > > > would fail in that case.
    > > >
    > > > The driver is broken then. It is supposed to retry with a small
    > > > mask on an error. Please fix the driver.
    > >
    > > I already added a workaround to the driver.
    > > Why do we need to workaround this in _every_ driver? (Note that _every_
    > > driver supporting a 64bit mask is affected). Why not fix it in the DMA layer?
    > Some hardware wants to know it can get a given DMA mask or failure. I
    > agree however that a "pci_prefer_64bit_dma(pdev)" function would be a
    > good patch for someone to submit tot he PCI layer code.

    Yeah well. I see the issue. However, I think the actual probing should
    be done in the DMA layer. We could pass dma_set_mask() the mask as a pointer
    and modify the mask value to what is actually used. So the driver would
    know what mask we felt back to. That was actually my first idea,
    but I preferred to submit a more simple solution without an API change
    to the list.

    However, in the end I don't care too much, as our driver is fixed.
    I just think that we will have more of these bugs in the future. Especially,
    as this bug won't hit on the majority of platforms.

    Greetings Michael.

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