ARM: 2.6.3[45] PCI regression (IXP4xx and PXA?)

Russell King - ARM Linux
2010-08-15T08:23:28Z

On Sun, Aug 15, 2010 at 02:42:51PM +0900, FUJITA Tomonori wrote:
> 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?

Why bother when we both agree that the patch is a dirty hack?

Come up with something cleaner first.