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    SubjectRe: ARM: 2.6.3[45] PCI regression (IXP4xx and PXA?)
    On Sat, 14 Aug 2010 19:46:05 +0100
    Russell King - ARM Linux <> wrote:

    > On Sat, Aug 14, 2010 at 06:30:37PM +0900, FUJITA Tomonori wrote:
    > > On Fri, 13 Aug 2010 22:54:13 +0100
    > > Russell King - ARM Linux <> wrote:
    > > > This means that when dmabounce comes to allocate the replacement
    > > > buffer, it gets a buffer which won't be accessible to the DMA
    > > > controller
    > >
    > > Really? looks like dmabounce does nothing for coherent memory that
    > > dma_alloc_coherent() allocates.
    > >
    > > The following very hacky patch works?
    > So what happens if you use a driver which uses dma_alloc_coherent()
    > directly? Should the driver really be passed memory which is
    > inaccessible to the device because its outside the host bridge PCI
    > window?

    I'm not sure what you mean.

    A driver which uses dma_alloc_coherent() directly should
    work. dma_alloc_coherent() allocates memory with GFP_DMA with that
    patch for dmabounce devices. So the driver gets the access-able

    The memory that dma_alloc_coherent() returns should be always
    consistent. We can't bounce it. All we can do is returning a memory
    that a device (and its bus) can access to.

    Krzysztof, can you try the patch?

    > No, this is clearly wrong, so this patch doesn't fix anything. It's
    > a bodge, nothing more. The real solution is to have _both_ masks
    > both reduced down according to the host bridge, as we used to do.
    > So I suggest 6fee48c is reverted so that these platforms don't regress
    > for -rc1.

    Sorry, the original ARM code is wrong. dev->dma_mask and
    dev->coherent_dma_mask represent the driver of dma restriction. ARM
    tries to use them for both a driver and a bus so ARM needs a
    workaround that doesn't set the driver of dma restriction to
    dev->dma_mask and dev->coherent_dma_mask.

    The proper solution is having a separate dma mask for a bus. I think
    that POWERPC already does the similar. It has max_direct_dma_addr in
    struct dev_archdata, which represents the dma restriction of a bus.

     \ /
      Last update: 2010-08-15 07:45    [W:0.020 / U:4.712 seconds]
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