From mboxrd@z Thu Jan  1 00:00:00 1970
From: Santosh Shilimkar <santosh.shilimkar@ti.com>
Subject: Re: [PATCH 3/7] of: introduce of_dma_is_coherent() helper
Date: Fri, 7 Mar 2014 12:18:48 +0800
Message-ID: <531948A8.9040106@ti.com>
References: <1394097598-17622-1-git-send-email-santosh.shilimkar@ti.com>	<1394097598-17622-4-git-send-email-santosh.shilimkar@ti.com>	<CAL_JsqJnG1c0=+UgOmNOGs7a5jv2f3O074-TsXibiHsXapXhcQ@mail.gmail.com>	<53194092.7010809@ti.com>
 <CAL_JsqJ3QhRRNVAsvAPP=Ex_ptQcbpCXh7pf44K1xh+scFqiug@mail.gmail.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Return-path: <linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org>
In-Reply-To: <CAL_JsqJ3QhRRNVAsvAPP=Ex_ptQcbpCXh7pf44K1xh+scFqiug@mail.gmail.com>
List-Unsubscribe: <http://lists.infradead.org/mailman/options/linux-arm-kernel>,
 <mailto:linux-arm-kernel-request@lists.infradead.org?subject=unsubscribe>
List-Archive: <http://lists.infradead.org/pipermail/linux-arm-kernel/>
List-Post: <mailto:linux-arm-kernel@lists.infradead.org>
List-Help: <mailto:linux-arm-kernel-request@lists.infradead.org?subject=help>
List-Subscribe: <http://lists.infradead.org/mailman/listinfo/linux-arm-kernel>,
 <mailto:linux-arm-kernel-request@lists.infradead.org?subject=subscribe>
Sender: "linux-arm-kernel" <linux-arm-kernel-bounces@lists.infradead.org>
Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org
To: Rob Herring <robherring2@gmail.com>
Cc: "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>, Russell King <linux@arm.linux.org.uk>, Arnd Bergmann <arnd@arndb.de>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Linus Walleij <linus.walleij@linaro.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, Grant Likely <grant.likely@linaro.org>, Rob Herring <robh+dt@kernel.org>, Catalin Marinas <catalin.marinas@arm.com>, Olof Johansson <olof@lixom.net>, "linux-arm-kernel@lists.infradead.org" <linux-arm-kernel@lists.infradead.org>
List-Id: devicetree@vger.kernel.org

On Friday 07 March 2014 11:55 AM, Rob Herring wrote:
> On Thu, Mar 6, 2014 at 9:44 PM, Santosh Shilimkar
> <santosh.shilimkar@ti.com> wrote:
>> On Friday 07 March 2014 11:13 AM, Rob Herring wrote:
>>> On Thu, Mar 6, 2014 at 3:19 AM, Santosh Shilimkar
>>> <santosh.shilimkar@ti.com> 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
>>> DMA_NONCOHERENT.
>>>
>> 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.

Regards,
Santosh