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

Herbert Xu
2014-07-24T01:41:55Z

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@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
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