linux-kernel - Re: [PATCH] pci: print out DMA mask info

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Date:	Sun, 12 Oct 2008 01:38:59 -0600
From:	Grant Grundler <grundler@...isc-linux.org>
To:	Roland Dreier <rdreier@...co.com>
Cc:	Matthew Wilcox <matthew@....cx>, Yinghai Lu <yinghai@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	grundler@...isc-linux.org, mingo@...e.hu, tglx@...utronix.de,
	hpa@...or.com, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org
Subject: Re: [PATCH] pci: print out DMA mask info

On Fri, Oct 10, 2008 at 10:18:33AM -0700, Roland Dreier wrote:
>  > Open-coding DMA_BIT_MASK() within your driver means that we no longer
>  > have a canonical list of DMA masks in one place.  Instead we have to
>  > grep the entire tree and come up with more-or-less complex scripts to
>  > figure out which bit masks are actually in use.
> 
> Out of curiousity, why do we care about that list?

Originally, I used to track down IO perf issues when porting drivers to ia64.

But knowing the dma masks in use on specific platforms might allow
folks to disable DMA_ZONE (like ia64 since it's always guarateed
either a SWIOTLB or real IOMMU).

Any other uses?

thanks,
grant

> 
>  - R.
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