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

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Date:	Thu, 1 May 2008 11:36:18 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Michael Buesch <mb@...sch.de>
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 Thu, May 01, 2008 at 04:38:15PM +0200, Michael Buesch wrote:
> This patchset adds API and one user for a "weak" dma_set_mask().
> Weak means that it will fallback to smaller masks in case the
> DMA subsystem rejects a big mask.
> Currently such rejection may happen if the driver requests a 64bit
> mask on a VIA machine, for example. dma_set_mask_weak() will fallback
> to 32bit, in that case, and tell the caller about it by modifying the
> passed mask.

Why do we need it?  Is the call to set the 32bit mask when it fails
a too big burden for the driver author?

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