linux-kernel - Re: [PATCH 0/3] Add API for weak DMA masks

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Date:	Thu, 1 May 2008 18:07:25 +0200
From:	Michael Buesch <mb@...sch.de>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Jesse Barnes <jbarnes@...tuousgeek.org>,
	John Linville <linville@...driver.com>,
	Andi Kleen <andi@...stfloor.org>,
	David Miller <davem@...emloft.net>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Ingo Molnar <mingo@...e.hu>, bcm43xx-dev@...ts.berlios.de,
	linux-wireless@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/3] Add API for weak DMA masks

On Thursday 01 May 2008 17:58:26 Christoph Hellwig wrote:
> On Thu, May 01, 2008 at 05:47:26PM +0200, Michael Buesch wrote:
> > We've discussed that and this behaviour is not acceptable, as the driver
> > must know about a possible fallback in case it can do 32bit DMA
> > more efficiently than 64bit DMA, for example.
> 
> That's what we have dma_get_required_mask() for.  See
> Documentation/DMA-API.txt.

So well. I'm still unsure about the advantage of having some opencoded
probe loop in the driver, instead of implementing it in a common place
and doing all of it with a single API call.
We can still call dma_get_required_mask() and adjust the mask to that
in dma_set_mask_weak(). That can _additionally_ be done there.

-- 
Greetings Michael.
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