linux-kernel - Re: ARM: 2.6.3[45] PCI regression (IXP4xx and PXA?)

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Message-ID: <20100815082328.GA12222@n2100.arm.linux.org.uk>
Date:	Sun, 15 Aug 2010 09:23:28 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
Cc:	khc@...waw.pl, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-arch@...r.kernel.org
Subject: Re: ARM: 2.6.3[45] PCI regression (IXP4xx and PXA?)

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@....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@....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.
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