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Date:	Fri, 7 Mar 2014 12:18:48 +0800
From:	Santosh Shilimkar <>
To:	Rob Herring <>
CC:	Arnd Bergmann <>,
	"" <>,
	"" <>,
	Greg Kroah-Hartman <>,
	Russell King <>,
	Olof Johansson <>,
	Grant Likely <>,
	Rob Herring <>,
	Catalin Marinas <>,
	Linus Walleij <>
Subject: Re: [PATCH 3/7] of: introduce of_dma_is_coherent() helper

On Friday 07 March 2014 11:55 AM, Rob Herring wrote:
> On Thu, Mar 6, 2014 at 9:44 PM, Santosh Shilimkar
> <> wrote:
>> On Friday 07 March 2014 11:13 AM, Rob Herring wrote:
>>> On Thu, Mar 6, 2014 at 3:19 AM, Santosh Shilimkar
>>> <> wrote:
>>>> The of_dma_is_coherent() helper parses the given DT device
>>>> node to see if the "dma-coherent" property is supported and
>>>> returns true or false accordingly.
>>>> For the architectures which are fully dma coherent and don't need per device
>>>> property, it can enable CONFIG_ARCH_IS_DMA_COHERENT config option which
>>>> enables DMA coherent for all devices by default.
>>> This worries me. I killed off arch_is_coherent() for arm. Now we're
>>> adding something back. Also, we already have HAVE_GENERIC_DMA_COHERENT
>>> which is different, but the names will be confusing. MIPS also has
>> Thanks for comments Rob. I will address them in next version.
>> Specifically about ARCH_IS_DMA_COHERENT, I wasn't very comfortable either
>> while adding it. But as Arnd mentioned, there is a need to have a way
>> for the arch's which are fully coherent to use coherent ops by default.
>> Am not sure whats the best way to have such support without imposing
>> any special updates on such arches.
> Thinking about this some more, if the arch is always coherent or
> always non-coherent, then the default ops are always fine. In that
> case set_arch_dma_coherent_ops is always a nop and of_dma_is_coherent
> is a don't care.
Hmmm.. I guess you are right. In that case we can drop the need of
config option.

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