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

From: "Luis R. Rodriguez" <mcgrof@kernel.org>
To: Christoph Hellwig <hch@infradead.org>
Cc: "Luis R. Rodriguez" <mcgrof@kernel.org>,
	Krzysztof Kozlowski <k.kozlowski@samsung.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Russell King <rmk+kernel@arm.linux.org.uk>,
	Robin Murphy <robin.murphy@arm.com>,
	Marek Szyprowski <m.szyprowski@samsung.com>,
	Doug Anderson <armlinux@m.disordat.com>,
	Will Deacon <will.deacon@arm.com>, Joerg Roedel <jroedel@suse.de>,
	Christian Borntraeger <borntraeger@de.ibm.com>,
	Zhen Lei <thunder.leizhen@huawei.com>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Andy Lutomirski <luto@kernel.org>,
	linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 01/44] dma-mapping: Use unsigned long for dma_attrs
Date: Mon, 13 Jun 2016 19:41:40 +0200	[thread overview]
Message-ID: <20160613174140.GM11948@wotan.suse.de> (raw)
In-Reply-To: <20160613160041.GA23851@infradead.org>

On Mon, Jun 13, 2016 at 09:00:41AM -0700, Christoph Hellwig wrote:
> 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.

History shows only sparse use of extensions of these these attributes so I
think the approach with a typedef is definitely more suitable for this API, and
should last long enough. The added gain of the annotation is a nice bonus.

  Luis