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

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Date:	Wed, 23 Jul 2014 21:38:35 +0200
From:	Marek Vasut <marex@...x.de>
To:	Corentin LABBE <clabbe.montjoie@...il.com>
Cc:	Herbert Xu <herbert@...dor.apana.org.au>, 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 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.

Best regards,
Marek Vasut
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