linux-kernel - Re: [PATCH v3 0/6] Add support for MCRC64 engine to calculate 64-bit CRC in Full-CPU mode

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Date: Mon, 10 Jun 2024 20:13:14 -0700
From: Eric Biggers <ebiggers@...nel.org>
To: Herbert Xu <herbert@...dor.apana.org.au>
Cc: Kamlesh Gurudasani <kamlesh@...com>, kristo@...nel.org, will@...nel.org,
	akpm@...ux-foundation.org, davem@...emloft.net,
	mcoquelin.stm32@...il.com, alexandre.torgue@...s.st.com,
	robh@...nel.org, krzysztof.kozlowski+dt@...aro.org,
	conor+dt@...nel.org, vigneshr@...com, catalin.marinas@....com,
	linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
	linux-stm32@...md-mailman.stormreply.com,
	linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v3 0/6] Add support for MCRC64 engine to calculate 64-bit
 CRC in Full-CPU mode

On Tue, Jun 11, 2024 at 10:31:45AM +0800, Herbert Xu wrote:
> On Mon, Jun 10, 2024 at 08:03:44PM +0530, Kamlesh Gurudasani wrote:
> > <kamlesh@...com> writes:
> > 
> > > From: Kamlesh Gurudasani <kamlesh@...com>
> > >
> > > MCRC64 engine calculates 64-bit cyclic redundancy checks (CRC)
> > > according to the ISO 3309 standard.
> > 
> > Could you please review this and let me know if any changes are needed
> > to get it merged.
> 
> Eric Biggers had concerns about adding this to the kernel.  I'd
> like know if he's OK with this or not.
> 

I thought the rule is that there needs to be an in-kernel user to add algorithms
to the crypto API?  Is there any precedent for adding new algorithms purely so
that accelerators that implement them can be accessed from userspace via AF_ALG?

Even if acceptable, the motivation for this one does seem weak, given that a
userspace software implementation would actually be faster.  It could be
marginally useful for freeing up the CPU for other tasks if the inputs being
processed are very large (probably at least several megabytes), though.

- Eric