linux-kernel - Re: [PATCH 09/11] crypto: remove LZO fallback from crypto 842

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Message-ID: <20150408143831.GA30762@gondor.apana.org.au>
Date:	Wed, 8 Apr 2015 22:38:31 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Dan Streetman <ddstreet@...e.org>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Michael Ellerman <mpe@...erman.id.au>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Seth Jennings <sjennings@...iantweb.net>,
	Robert Jennings <rob@...hix.net>, linux-crypto@...r.kernel.org,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 09/11] crypto: remove LZO fallback from crypto 842

On Wed, Apr 08, 2015 at 10:28:23AM -0400, Dan Streetman wrote:
> 
> So, the sw implementation is only for decompression; there's no sw
> compression implementation in these patches.

As a general rule we don't add any hardware implementation unless
there is a software implementation.  The reason is that every new
algorithm creates an API (potentially a user-space API if the
algorithm can be exported via algif).  But sometimes things slip
through.

So I'm not going to immediately remove 842 but it would be nice
if we had a reference implementation so that if ever there were
another hardware 842 implmentation added then at least we have
something that we can judge against.

> The hw 842 driver is currently at drivers/crypto/nx, and the
> crypto/842 driver just calls the hw driver (after correctly
> aligning/sizing the provided buffers to what the hw driver expects),
> and falls back to the sw decompression if the hw decompression fails
> (there is no compression fallback, a failure is reported to the
> caller).
> 
> Is that setup ok?  If users had to directly call the hw driver,
> instead of using the generic crypto_comp interface, it would
> complicate things, e.g. in zswap it only expects to call
> crypto_comp_compress()/decompress(), not call the 842 hw driver
> directly.

I think the only thing that needs to happen for now is moving
crypto/842.c over to drivers/crypto/nx (perhaps merge it into
nx-842.c) so that it's obvious that this is not a generic
implementation.

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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