Re: crypto API and IBM z990 hardware support

[Christoph Hellwig <hch@infradead.org>]

On Wed, Jul 02, 2003 at 07:35:16PM +1000, James Morris wrote:
> The plan is to provide crypto/arch/ subdirectories where arch optimized 
> versions of the crypto algorithms are implemented, and built automatically 
> (via configuration defaults) instead of the generic C versions.
> 
> So, there might be:
> 
> crypto/aes.c
> crypto/arch/i386/aes.s

crypto/arch/ sounds like a bad idea.  We really should avoid arch code
outside arch/ and include/asm*.  So arch/<foo>/crypto/ as suggested by
Thomas is much better.

> where on i386, aes.s would be built into aes.o and aes.c would not be 
> built.

That's a really bad idea.  Think of a i586/i686 optimized assembler
implementaion e.g. using MMX or SSE or whatever.  You'll always need
the generic version as fallback.

> The simple solution for you might be something like:
> 
> crypto/aes.c -> aes.o
> crypto/arch/s390/aes_z990.c -> aes_z990.o
> 
> and the administrator of the system could configure modprobe.conf to alias 
> aes to aes_z990 if the latter is supported in hardware.

Right.  And IMHO this should happen with all optimized version - putting
policy in the kernel to select them sounds like a bad idea, especially
as it could get rather complicated when it involves multiple optimized
and / or hardware implementations.