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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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