Messages in this thread | | | Date | Fri, 13 Aug 2010 22:54:13 +0100 | From | Russell King - ARM Linux <> | Subject | Re: ARM: 2.6.3[45] PCI regression (IXP4xx and PXA?) |
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On Fri, Aug 13, 2010 at 03:23:53PM +0900, FUJITA Tomonori wrote: > On Wed, 11 Aug 2010 08:25:32 +0100 > Russell King - ARM Linux <linux@arm.linux.org.uk> wrote: > > It doesn't break dmabounce. > > > > What it breaks is the fact that a PCI device which can do 32-bit DMA is > > connected to a PCI bus which can only access the first 64MB of memory > > through the host bridge, but the system has more than 64MB available. > > > > Allowing a 32-bit DMA mask means that dmabounce can't detect that memory > > above 64MB needs to be bounced to memory below the 64MB boundary. > > But dmabounce doesn't look at dev->coherent_dma_mask. > > The change breaks __dma_alloc_buffer()? If we set dev->coherent_dma_mask > to DMA_BIT_MASK(32) for ixp4xx's pci devices, __dma_alloc_buffer() > doesn't use GFP_DMA.
With an incorrect coherent_dma_mask, dma_alloc_coherent() will return memory outside of the 64MB window. This means that when dmabounce comes to allocate the replacement buffer, it gets a buffer which won't be accessible to the DMA controller - which is a condition it doesn't check for.
Ergo, it breaks dmabounce.
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