AW: SPE & Interrupt context (was how to make use of SPE instructions)

[Markus Stockhausen]

> > Von: Scott Wood [scottwood at freescale.com]
> > Gesendet: Mittwoch, 28. Januar 2015 05:21
> > An: Markus Stockhausen
> > Cc: Michael Ellerman; linuxppc-dev at lists.ozlabs.org; Herbert Xu
> > Betreff: Re: SPE & Interrupt context (was how to make use of SPE instructions)
> > 
> > Hi Scott,
> >
> > thanks for your helpful feedback. As you might have seen I sent a first
> > patch for the sha256 kernel module that takes care about preemption.
> >
> > Herbert Xu noticed that my module won't run in for IPsec as all
> > work will be done from interrupt context. Do you have a tip how I can
> > mitigate the check I implemented:
> >
> > static bool spe_usable(void)
> > {
> >   return !in_interrupt();
> > }
> >
> > Intel guys have something like that
> >
> > bool irq_fpu_usable(void)
> > {
> >   return !in_interrupt() ||
> >     interrupted_user_mode() ||
> >     interrupted_kernel_fpu_idle();
> > }
> >
> > But I have no idea how to transfer it to the PPC/SPE case.
> 
> I'm not sure what sort of tip you're looking for, other than
> implementing it myself. :-)

Hi Scott,

maybe I did not explain it correctly. interrupted_kernel_fpu_idle()
is x86 specific. The same applies to interrupted_user_mode().
I'm just searching for a similar feature in the PPC/SPE world.
I can see that enable_kernel_spe() does something with the
MSR_SPE flag, but I have no idea  how to determine if I'm allowed
to enable SPE although I'm inside an interrupt context.

I'm asking because from the previous posts I conclude that 
running SPE instructions inside an interrupt might be critical. 
Because of registers not being saved?

Or can I just save the register contents myself and interrupt
context is no longer a showstopper?

Markus


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