Messages in this thread | | | Date | Sun, 15 Aug 2010 14:42:51 +0900 | Subject | Re: ARM: 2.6.3[45] PCI regression (IXP4xx and PXA?) | From | FUJITA Tomonori <> |
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On Sat, 14 Aug 2010 19:46:05 +0100 Russell King - ARM Linux <linux@arm.linux.org.uk> 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 <linux@arm.linux.org.uk> 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 memory.
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.
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