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Subject: Re: [PATCH 2/3] powerpc/85xx: Provide two functions to save/restore
 the core registers
From: Scott Wood <scottwood@freescale.com>
To: Wang Dongsheng-B40534 <Dongsheng.Wang@freescale.com>
Date: Thu, 23 Jan 2014 10:22:45 -0600
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Cc: "anton@enomsg.org" <anton@enomsg.org>,
 "linuxppc-dev@lists.ozlabs.org" <linuxppc-dev@lists.ozlabs.org>, Zhao
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On Wed, 2014-01-22 at 20:49 -0600, Wang Dongsheng-B40534 wrote:
> > > >
> > > > The whole point of calling enable_kernel_fp() in C code before
> > > > suspending is to ensure that the FP state gets saved.  If FP is used
> > > > after that point it is a bug.  If you're worried about such bugs, then
> > > > clear MSR[FP] after calling enable_kernel_fp(), rather than adding
> > > > redundant state saving.
> > > >
> > >
> > > enable_kernel_fp() calling in MEM suspend flow.
> > > Hibernation is different with MEM suspend, and I'm not sure where will call
> > this
> > > interface, so we need to ensure the integrity of the core saving. I don't
> > think
> > > this code is *redundant*. I trust that the kernel can keep the FP related
> > > operations, that's why a judgment is here. :)
> > 
> > For hibernation, save_processor_state() is called first, which does
> > flush_fp_to_thread() which has a similar effect (though I wonder if it's
> > being called on the correct task for non-SMP).
> > 
> Yes, thanks, I miss this code.:)
> 
> But I still think we need to keep this judgment, because i provide an API.
> If you still insist on I can remove *FP*, but I don't want to do this..:)

I insist.  Redundant code wastes review and maintenance bandwidth, and
is a potential source of bugs.

-Scott