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    SubjectRe: 2.6.26-rc1 regression: ISA DMA broken (bisected)
    Date
    On Friday 09 May 2008 12:06:55 am Takashi Iwai wrote:
    > Thanks for catching it. Yeah, the patch looks buggy. We had an
    > implicit assumption that dev = NULL for ISA devices that require 24bit
    > DMA.

    Naive question #1: Why don't we have a struct device for these
    ISA devices? PNP builds a struct device with DMA_24BIT_MASK
    for ISAPNP devices.

    Naive question #2: Do other architectures need similar fixes in
    dma_alloc_coherent()?

    > [PATCH] x86: Fix dma_alloc_coherent() for ISA devices
    >
    > The recent work on x86 dma_alloc_coherent() breaks the ISA DMA buffer
    > allocation, which is represented by "dev = NULL" and requires 24bit
    > DMA implicitly.
    >
    > Signed-off-by: Takashi Iwai <tiwai@suse.de>
    >
    > ---
    >
    > diff --git a/arch/x86/kernel/pci-dma.c b/arch/x86/kernel/pci-dma.c
    > index 0c37f16..c5ef1af 100644
    > --- a/arch/x86/kernel/pci-dma.c
    > +++ b/arch/x86/kernel/pci-dma.c
    > @@ -385,11 +385,13 @@ dma_alloc_coherent(struct device *dev, size_t size, dma_addr_t *dma_handle,
    > if (dma_alloc_from_coherent_mem(dev, size, dma_handle, &memory))
    > return memory;
    >
    > - if (!dev)
    > + if (!dev) {
    > dev = &fallback_dev;
    > + gfp |= GFP_DMA;
    > + }
    > dma_mask = dev->coherent_dma_mask;
    > if (dma_mask == 0)
    > - dma_mask = DMA_32BIT_MASK;
    > + dma_mask = (gfp & GFP_DMA) ? DMA_24BIT_MASK : DMA_32BIT_MASK;
    >
    > /* Device not DMA able */
    > if (dev->dma_mask == NULL)
    > @@ -403,7 +405,7 @@ dma_alloc_coherent(struct device *dev, size_t size, dma_addr_t *dma_handle,
    > larger than 16MB and in this case we have a chance of
    > finding fitting memory in the next higher zone first. If
    > not retry with true GFP_DMA. -AK */
    > - if (dma_mask <= DMA_32BIT_MASK)
    > + if (dma_mask <= DMA_32BIT_MASK && !(gfp & GFP_DMA))
    > gfp |= GFP_DMA32;
    > #endif
    >



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