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Date: Fri, 10 Jun 2016 16:49:47 +0200
From: "Luis R. Rodriguez" <mcgrof@kernel.org>
To: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, hch@infradead.org,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
        Jonathan Corbet <corbet@lwn.net>,
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        Marek Szyprowski <m.szyprowski@samsung.com>,
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        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
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On Fri, Jun 10, 2016 at 12:11:18PM +0200, Krzysztof Kozlowski wrote:
> The dma-mapping core and the implementations do not change the
> DMA attributes passed by pointer.  Thus the pointer can point to const
> data.  However the attributes do not have to be a bitfield. Instead
> unsigned long will do fine:
> 
> 1. This is just simpler.  Both in terms of reading the code and setting
>    attributes.  Instead of initializing local attributes on the stack
>    and passing pointer to it to dma_set_attr(), just set the bits.
> 
> 2. It brings safeness and checking for const correctness because the
>    attributes are passed by value.

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 ?

If the concern is the const data, why not require const struct dma_attr
for the APIs that we know can and should use const ?

  Luis