How to make use of SPE instructions?

[Markus Stockhausen]

Hello,

I developed a SHA224/256 kernel crypto module with SPE instructions.
The result looks quite promising (~ +50% speedup). Nevertheless the
flooding of kernel messages "SPE used in kernel" makes me feel 
uncomfortable.

My findings so far:

- I can configure the kernel with "SPE support". 
- arch/powerpc/kernel/head_fsl_booke.S suggests that the message is
  triggerd unconditionally whenwever we make use of SPE in kernel.
- There exists a function enable_kernel_spe() but I don't know how
  this could help me in my work.

I guess I need some kind of "brackets" around my coding to make sure 
the upper 32 bit of the registers are stored correctly during task switch. 
Or is the use of SPE instructions inside the kernel totally forbidden? Any 
expert with some helpful advise?

Thanks in advance.

Markus
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