[PATCH 2/3] powerpc/85xx: Provide two functions to save/restore the core registers

[Scott Wood]

On Mon, 2014-01-20 at 20:43 -0600, Wang Dongsheng-B40534 wrote:
> 
> > -----Original Message-----
> > From: Wood Scott-B07421
> > Sent: Tuesday, January 21, 2014 9:06 AM
> > To: Wang Dongsheng-B40534
> > Cc: benh at kernel.crashing.org; Zhao Chenhui-B35336; anton at enomsg.org; linuxppc-
> > dev at lists.ozlabs.org
> > Subject: Re: [PATCH 2/3] powerpc/85xx: Provide two functions to save/restore the
> > core registers
> > 
> > On Mon, 2014-01-20 at 00:03 -0600, Wang Dongsheng-B40534 wrote:
> > > > > > > +	/*
> > > > > > > +	 * Need to save float-point registers if MSR[FP] = 1.
> > > > > > > +	 */
> > > > > > > +	mfmsr	r12
> > > > > > > +	andi.	r12, r12, MSR_FP
> > > > > > > +	beq	1f
> > > > > > > +	do_sr_fpr_regs(save)
> > > > > >
> > > > > > C code should have already ensured that MSR[FP] is not 1 (and thus the
> > FP
> > > > > > context has been saved).
> > > > > >
> > > > >
> > > > > Yes, right. But I mean if the FP still use in core save flow, we need to
> > save
> > > > it.
> > > > > In this process, i don't care what other code do, we need to focus on not
> > > > losing
> > > > > valuable data.
> > > >
> > > > It is not allowed to use FP at that point.
> > > >
> > > If MSR[FP] not active, that is FP not allowed to use.
> > > But here is a normal judgment, if MSR[FP] is active, this means that the
> > floating
> > > point module is being used. I offer is a function of the interface, we don't
> > know
> > > where is the function will be called. Just because we call this function in
> > the
> > > context of uncertainty, we need this judgment to ensure that no data is lost.
> > 
> > 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).

-Scott