From: Radu Andrei Alexe <radu.alexe-3arQi8VN3Tc@public.gmane.org>
Subject: Re: [PATCH RESEND 1/4] crypto: caam: add caam-dma node to SEC4.0
 device tree binding
Date: Fri, 10 Nov 2017 08:02:01 +0000
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References: <20171030134654.13729-1-horia.geanta@nxp.com>
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Cc: =?iso-8859-2?Q?Horia_Geant=E3?= <horia.geanta-3arQi8VN3Tc@public.gmane.org>,
        Vinod Koul <vinod.koul-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>,
        Herbert Xu <herbert-lOAM2aK0SrRLBo1qDEOMRrpzq4S04n8Q@public.gmane.org>,
        "David S. Miller" <davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org>,
        Dan Douglass <dan.douglass-3arQi8VN3Tc@public.gmane.org>,
        Shawn Guo <shawnguo-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
        "dmaengine-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" <dmaengine-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
        "linux-crypto-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" <linux-crypto-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
        "devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" <devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
To: Kim Phillips <kim.phillips-5wv7dgnIgG8@public.gmane.org>
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List-Id: linux-crypto.vger.kernel.org

On 11/9/2017 6:34 PM, Kim Phillips wrote:=0A=
> On Thu, 9 Nov 2017 11:54:13 +0000=0A=
> Radu Andrei Alexe <radu.alexe-3arQi8VN3Tc@public.gmane.org> wrote:=0A=
> =0A=
>> On 10/30/2017 4:24 PM, Kim Phillips wrote:=0A=
>>> On Mon, 30 Oct 2017 15:46:51 +0200=0A=
>>> Horia Geant=E3 <horia.geanta-3arQi8VN3Tc@public.gmane.org> wrote:=0A=
>>>=0A=
>>>> +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=0A=
>>>> +CAAM DMA Node=0A=
>>>> +=0A=
>>>> +    Child node of the crypto node that enables the use of the DMA cap=
abilities=0A=
>>>> +    of the CAAM by a stand-alone driver. The only required property i=
s the=0A=
>>>> +    "compatible" property. All the other properties are determined fr=
om=0A=
>>>> +    the job rings on which the CAAM DMA driver depends (ex: the numbe=
r of=0A=
>>>> +    dma-channels is equal to the number of defined job rings).=0A=
>>>> +=0A=
>>>> +  - compatible=0A=
>>>> +      Usage: required=0A=
>>>> +      Value type: <string>=0A=
>>>> +      Definition: Must include "fsl,sec-v4.0-dma"=0A=
>>>> +=0A=
>>>> +EXAMPLE=0A=
>>>> +  caam-dma {=0A=
>>>> +    compatible =3D "fsl,sec-v5.4-dma",=0A=
>>>> +                 "fsl,sec-v5.0-dma",=0A=
>>>> +                 "fsl,sec-v4.0-dma";=0A=
>>>> +  }=0A=
>>>=0A=
>>> If this isn't describing an aspect of the hardware, then what is it=0A=
>>> doing in the device tree?=0A=
>>>=0A=
>>> Kim=0A=
>>>=0A=
>>=0A=
>> Because the caam_dma driver is a platform driver I needed to create a=0A=
>> platform device to activate the driver. My thought was that it was=0A=
>> simpler to implement it using device tree.=0A=
>> The next patch version will create the platform device dynamically at=0A=
>> run time.=0A=
> =0A=
> Why create a new device when that h/w already has one?=0A=
> =0A=
> Why doesn't the existing crypto driver register dma capabilities with=0A=
> the dma driver subsystem?=0A=
> =0A=
> Kim=0A=
> =0A=
=0A=
=0A=
I can think of two reasons:=0A=
=0A=
1. The code that this driver introduces has nothing to do with crypto =0A=
and everything to do with dma. Placing the code in the same directory as =
=0A=
the caam subsystem would only create confusion for the reader of an =0A=
already complex driver.=0A=
=0A=
2. I wanted this driver to be tracked by the dma engine team. They have =0A=
the right expertise to provide adequate feedback. If all the code was in =
=0A=
the crypto directory they wouldn't know about this driver or any =0A=
subsequent changes to it.=0A=
=0A=
BR,=0A=
Radu=0A=
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