Message-ID: <CALZtONBYYTnRE6FyQKVL8kyAAb8BuXJzyGA5mYNHiXtSNcDv9Q@mail.gmail.com>
Date:	Tue, 22 Sep 2015 10:39:53 -0400
From:	Dan Streetman <ddstreet@...e.org>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Haren Myneni <haren@...ux.vnet.ibm.com>,
	"David S. Miller" <davem@...emloft.net>,
	Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Haren Myneni <hbabu@...ibm.com>
Subject: Re: [PATCH] drivers/crypto/nx: Add CRC and validation support for nx842

On Tue, Sep 22, 2015 at 8:21 AM, Herbert Xu <herbert@...dor.apana.org.au> wrote:
> On Mon, Sep 21, 2015 at 11:21:14AM -0400, Dan Streetman wrote:
>>
>> As far as the hw and sw drivers producing the exact same output, I
>> don't think that's possible with the current hw and sw drivers,
>> because the hw driver may have to add a header to the actual byte
>> stream that the hw creates, depending on buffer alignment and size
>> (the hw has specific restrictions).  Currently, the sw driver doesn't
>> understand that header that the 842 hw driver creates, although that
>> could be added to the sw driver.  And, the hw driver skips adding the
>> header if the buffers are correctly aligned/sized, which would result
>> in a test vector failure if it doesn't align the buffer the same way
>> each time.
>
> I guess they don't have to be exactly the same.  As long as each
> can take the output of the other and compress/decompress them it
> should be fine.

The hw driver code that handles the re-aligning and re-sizing, and
creating the header, is (mostly) isolated from the code that actually
talks to the NX 842 coprocessor, it's in drivers/crypto/nx/nx-842.c.

Haren, you could change the 842 sw driver to use that code to parse
compressed 842 buffers.  You'll have to modify the nx-842.c code some
though, as it expects to not only parse the header but also re-align
and re-size input and output buffers, which the sw driver doesn't need
to do, it can process buffers with any alignment and size.  Maybe you
could split out the header processing code into somewhere common, and
leave the code in 842-nx.c that actually re-aligns and re-sizes the
buffers.


>
>> Also, it might be a good time to add what we talked about a while ago,
>> to push the alignment/size restrictions into the crypto compression
>> layer, by adding cra_alignmask and cra_blocksize support to
>> crypto/compress.c.  Since the 842 hw has requirements not only for
>> specific alignment and min/max sizes, but also a requirement for
>> specific length multiple (i.e. must be !(len % 8)) it might be
>> worthwhile to also add a cra_sizemodulo or something like that.
>> However, if the common crypto alignment/size handling code allows any
>> alignment/size buffers (instead of just returning error for mis-sized
>> buffers), I think a common crypto header would need to be added in
>> cases of mis-sizing, which may not be appropriate for common code.
>> Alternately, the common crypto code could just return error for
>> mis-sized buffers; users of the crypto comp api would just have to
>> check crypto_tfm_alg_blocksize() before calling.
>
> I'd like to see another hardware implementation before we start
> moving this into the API.

ok.

>
>> In case I haven't said it before, I really hate how the 842 hw
>> requires specific alignment and sizing.  How hard is it to add support
>> for any alignment/size in the hw?!?
>
> Another option is to use a software fallback for the cases that
> the hardware can't handle.

hmm, that's true, and that would simplify the code a lot!  No need for
the header anymore.  But, since the sw driver is sooo much slower, it
would be important to be able to communicate the alignment and size
limits to the caller of the crypto compression api, via cra_alignmask
and cra_blocksize (for minimum size), as well as new fields for max
size (maybe cra_maxsize) and buffer length multiple - i.e. the buffer
length must be a multiple of N (maybe cra_blockmult or cra_blockmodulo
or something).  Otherwise callers would get unexpectedly slow
performance if they use the wrong alignment or size.

thanks!

>
> 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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