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

[Scott Wood]

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.

-Scott