Re: [linuxsh-dev] FPU in kernel (SH-4)

[Greg B. <gb...@po...>]

NIIBE Yutaka wrote:
> 
> The kernel has been changed since, this doesn't work any more, because
> of special kernel thread.  So far so good, as kernel threads do not do
> general things.  However, now we have ksoftirqd kernel threads, and it
> handles software interrupts (or bottom halves).  This means, ksoftirqd
> calls routines of drivers, and if we need using FPU in kernel, we need
> another approach.

  So, if we needed the FPU in the kernel, we'd have to switch FPU state
on context switch for kernel threads as well as user threads?

> I think that we should remove the support of FPU in kernel to clean up
> things. 

  Yes.  There's no good reason to have FPU support for the kernel.

  I seem to remember there was some issue with the Dreamcast framebuffer?

> I think that we can assume GCC provide some way of not using
> FPU for division.

  That's what -m4-nofpu is for, right?

> Honestly speaking, I couldn't find a good way to extend current
> implementation to general kernel FPU support (more than one kernel
> task uses FPU).  If we really need this, I think that it is good
> design general one rather than extending current one.

  Yes, but I don't think we need it.

Greg.
-- 
If it's a choice between being a paranoid, hyper-suspicious global
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