linux-kernel - Re: [PATCH v4 01/44] dma-mapping: Use unsigned long for dma

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Message-ID: <20160613160041.GA23851@infradead.org>
Date:	Mon, 13 Jun 2016 09:00:41 -0700
From:	Christoph Hellwig <hch@...radead.org>
To:	"Luis R. Rodriguez" <mcgrof@...nel.org>
Cc:	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	Andrew Morton <akpm@...ux-foundation.org>, hch@...radead.org,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Jonathan Corbet <corbet@....net>,
	Russell King <rmk+kernel@....linux.org.uk>,
	Robin Murphy <robin.murphy@....com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Doug Anderson <armlinux@...isordat.com>,
	Will Deacon <will.deacon@....com>,
	Joerg Roedel <jroedel@...e.de>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	Zhen Lei <thunder.leizhen@...wei.com>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Andy Lutomirski <luto@...nel.org>, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 01/44] dma-mapping: Use unsigned long for dma_attrs

On Fri, Jun 10, 2016 at 04:49:47PM +0200, Luis R. Rodriguez wrote:
> Do we not expect the number of argument to grow ? This "cleanup" would
> do away with such possibilities, and then require adding the API later,
> and this requiring a full set of collateral evolutions again when this
> is needed. What was the original motivation for using this instead of
> the approach you are suggesting ?

We still got plenty of space for attrs.  If you're worried about running
out of 32 flags we could do a dma_attrs_t typedef that we could swich
to a u64.  That would have another advantage in that we could add a
__bitwise sparse annotation to avoid people passing the wrong kind of
flags.