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

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Message-ID: <20140724014057.GA2448@gondor.apana.org.au>
Date:	Thu, 24 Jul 2014 09:40:57 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Marek Vasut <marex@...x.de>
Cc:	Corentin LABBE <clabbe.montjoie@...il.com>, 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

On Wed, Jul 23, 2014 at 09:38:35PM +0200, Marek Vasut wrote:
> On Wednesday, July 23, 2014 at 08:52:12 PM, Corentin LABBE wrote:
> > 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.
> 
> Yeah, in this case, using DMA and async interface combo is the way to go.

OK fair enough.
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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