linux-kernel - Re: [PATCH 3/3] crypto: Add Allwinner Security System crypto accelerator

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Date:	Wed, 23 Jul 2014 20:52:12 +0200
From:	Corentin LABBE <clabbe.montjoie@...il.com>
To:	Marek Vasut <marex@...x.de>,
	Herbert Xu <herbert@...dor.apana.org.au>
CC:	robh+dt@...nel.org, pawel.moll@....com, mark.rutland@....com,
	ijc+devicetree@...lion.org.uk, galak@...eaurora.org,
	rdunlap@...radead.org, maxime.ripard@...e-electrons.com,
	linux@....linux.org.uk, davem@...emloft.net,
	grant.likely@...aro.org, devicetree@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-crypto@...r.kernel.org
Subject: Re: [PATCH 3/3] crypto: Add Allwinner Security System crypto accelerator

Le 23/07/2014 17:51, Marek Vasut a écrit :
> On Wednesday, July 23, 2014 at 04:13:09 PM, Herbert Xu wrote:
>> On Wed, Jul 23, 2014 at 04:07:20PM +0200, Marek Vasut wrote:
>>> On Wednesday, July 23, 2014 at 03:57:35 PM, Herbert Xu wrote:
>>>> On Sat, May 24, 2014 at 02:00:03PM +0200, Marek Vasut wrote:
>>>>>> +	}
>>>>>> +#endif
>>>>>> +
>>>>>> +#ifdef CONFIG_CRYPTO_DEV_SUNXI_SS_MD5
>>>>>> +	err = crypto_register_shash(&sunxi_md5_alg);
>>>>>
>>>>> Do not use shash for such device. This is clearly and ahash (and
>>>>> async in general) device. The rule of a thumb here is that you use
>>>>> sync algos only for devices which have dedicated instructions for
>>>>> computing the transformation. For devices which are attached to some
>>>>> kind of bus, you use async algos (ahash etc).
>>>>
>>>> I'm sorry that I didn't catch this earlier but there is no such
>>>> rule.
>>>>
>>>> Unless you need the async interface you should stick to the sync
>>>> interfaces for the sake of simplicity.
>>>>
>>>> We have a number of existing drivers that are synchronous but
>>>> using the async interface.  They should either be converted
>>>> over to the sync interface or made interrupt-driven if possible.
>>>
>>> Sure, but this device is interrupt driven and uses DMA to feed the crypto
>>> engine, therefore async, right ?
>>
>> If it's interrupt-driven, then yes it would certainly make sense to
>> be async.  But all I see is polling in the latest posting, was the
>> first version different?
> 
> I stand corrected then, sorry.
> 
> Is it possible to use DMA to feed the crypto accelerator, Corentin?
> 
> Best regards,
> Marek Vasut
> 

Yes, DMA is possible and will be implemented soon.
So if I have well understood, I keep using async interface.

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