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

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Date:	Fri, 27 Aug 2010 09:26:17 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	khc@...waw.pl
Cc:	fujita.tomonori@....ntt.co.jp, benh@...nel.crashing.org,
	linux@....linux.org.uk, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: ARM: 2.6.3[45] PCI regression (IXP4xx and PXA?)

On Thu, 26 Aug 2010 18:02:46 +0200
Krzysztof Halasa <khc@...waw.pl> wrote:

> FUJITA Tomonori <fujita.tomonori@....ntt.co.jp> writes:
> 
> > Lots of drivers call dma_set_coherent_mask with 64bit mask and then
> > call it with 32bit mask if 64bit mask fails.
> 
> Which seems strange to me. If the driver asks for 64-bit mask and the
> system can only give it 32-bits, why return an error? Every 32-bit
> address is also 64-bit, with the most significant bits simply cleared.

As I wrote, the DMA API simply wasn't designed in that way (let
architectures to clip the mask), I guess.

If it was, dma_set_coherent_mask might return the actual mask.
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