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

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Date:	Wed, 23 Jul 2014 21:57:35 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Marek Vasut <marex@...x.de>
Cc:	LABBE Corentin <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 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.

Cheers,
-- 
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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