linux-kernel - Re: [PATCH -mm] ssb: open-code dma_alloc

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Message-Id: <20100215201825M.fujita.tomonori@lab.ntt.co.jp>
Date:	Mon, 15 Feb 2010 20:18:41 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	mb@...sch.de
Cc:	fujita.tomonori@....ntt.co.jp, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, davem@...emloft.net,
	stefano.brivio@...imi.it, Larry.Finger@...inger.net,
	akpm@...ux-foundation.org
Subject: Re: [PATCH -mm] ssb: open-code dma_alloc_coherent

On Mon, 15 Feb 2010 12:03:41 +0100
Michael Buesch <mb@...sch.de> wrote:

> On Monday 15 February 2010 06:21:58 FUJITA Tomonori wrote:
> > This patch is against -mm since it depends on the DMA API changes in
> 
> I appreciate your efforts to remove bus-specific APIs.
> However, always keep in mind that a SSB bus might be running on a system
> where there's no PCI bus at all.

Yup, that's why we introduced the generic device model and the generic
DMA API is better.


> In the past we used the generic dma_... API for DMA operations on all
> SSB devices. This worked 99.9% of the time. _But_ it broke in really obscure
> cases where the architecture implementations _slightly_ differed between
> the generic dma and the pci variants.

Yeah, I know. There are some differences between the PCI DMA API and
the generic DMA API on some architectures.

My patchset in -mm fixes the above problem:

http://marc.info/?l=linux-kernel&m=126596737604808&w=2

http://git.kernel.org/?p=linux/kernel/git/tomo/linux-2.6-misc.git;a=blob;f=include/asm-generic/pci-dma-compat.h;h=ddfa9c5309229d171af63dcaf3872288fb4fa845;hb=refs/heads/pending

The PCI DMA API simply calls the generic DMA API. And all the
architectures that supports pci uses asm-generic/pci-dma-compat.h.

You can use the generic DMA API with any buses. I'll remove the PCI
DMA API in the long term.


Thanks,
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