[RFC PATCH 2/2] ARM: kernel: implement stack pointer save array through MPIDR hashing

[lorenzo.pieralisi@arm.com (Lorenzo Pieralisi)]

On Tue, Jun 04, 2013 at 06:30:30PM +0100, Nicolas Pitre wrote:
> On Tue, 4 Jun 2013, Lorenzo Pieralisi wrote:
> 
> > index 987dcf3..da1b65f 100644
> > --- a/arch/arm/kernel/sleep.S
> > +++ b/arch/arm/kernel/sleep.S
> > @@ -7,6 +7,48 @@
> >  	.text
> >  
> >  /*
> > + * Implementation of MPIDR hash algorithm through shifting
> > + * and OR'ing.
> > + *
> > + * @dst: register containing hash result
> > + * @rtemp0: scratch register 0
> > + * @rtemp1: scratch register 1
> > + * @rtemp2: scratch register 2
> > + * @rs0: register containing affinity level 0 bit shift
> > + * @rs1: register containing affinity level 1 bit shift
> > + * @rs2: register containing affinity level 2 bit shift
> > + * @mpidr: register containing MPIDR value
> > + * @mask: register containing MPIDR mask
> > + *
> > + * Pseudo C-code:
> > + *
> > + *u32 dst;
> > + *
> > + *compute_mpidr_hash(u32 rs0, u32 rs1, u32 rs2, u32 mpidr, u32 mask) {
> > + *	u32 rtemp0, rtemp1, rtemp2;
> > + *	u32 mpidr_masked = mpidr & mask;
> > + *	rtemp0 = mpidr_masked & 0xff;
> > + *	rtemp1 = mpidr_masked & 0xff00;
> > + *	rtemp2 = mpidr_masked & 0xff0000;
> > + *	dst = (rtemp0 >> rs0 | rtemp1 >> rs1 | rtemp2 >> rs2);
> > + *}
> > + */
> > +.macro compute_mpidr_hash dst, rtemp0, rtemp1, rtemp2, rs0, rs1, 
> rs2, mpidr, mask
> > +	and	\mpidr, \mpidr, \mask		@ mask out unused MPIDR bits
> > +	and	\rtemp0, \mpidr, #0xff		@ extracts aff0
> > +	and	\rtemp1, \mpidr, #0xff00	@ extracts aff1
> > +	and	\rtemp2, \mpidr, #0xff0000	@ extracts aff2
> > +  ARM(	mov	\dst, \rtemp0, lsr \rs0)	@ dst=aff0>>rs0
> > +  ARM(	orr	\dst, \dst, \rtemp1, lsr \rs1)	@ dst|=(aff1>>rs1)
> > +  ARM(	orr	\dst, \dst, \rtemp2, lsr \rs2)		@ dst|=(aff2>>rs2)
> > +THUMB(	mov	\rtemp0, \rtemp0, lsr \rs0)		@ aff0>>=rs0
> > +THUMB(	mov	\rtemp1, \rtemp1, lsr \rs1)		@ aff1>>=rs1
> > +THUMB(	mov	\rtemp2, \rtemp2, lsr \rs2)		@ aff2>>=rs2
> > +THUMB(	orr	\dst, \rtemp0, \rtemp1)			@ dst = aff0 | aff1
> > +THUMB(	orr	\dst, \dst, \rtemp2)			@ dts |= aff2
> > +.endm
> 
> This would be much nicer by useing fewer registers.  I'd suggest this 
> instead of guessing which registers can be duplicated in the 
> macro invokation:
> 
> .macro compute_mpidr_hash dst, rs0, rs1, rs2, mpidr, mask
> 	and	\mpidr, \mpidr, \mask		@ mask out unused MPIDR bits
> 	and	\dst, \mpidr, #0xff		@ extracts aff0
>    ARM(	mov	\dst, \dst, lsr \rs0 )	@ dst = aff0 >> rs0
>  THUMB(	lsr	\dst, \rs0 )
> 	and	\mask, \mpidr, #0xff00	@ extracts aff1
>    ARM(	orr	\dst, \dst, \mask, lsr \rs1 )	@ dst |= (aff1 >> rs1)
>  THUMB(	lsr	\mask, \rs1 )
>  THUMB(	orr	\dst, \mask )
> 	and	\mask, \mpidr, #0xff0000	@ extracts aff2
>    ARM(	orr	\dst, \dst, \mask, lsr \rs2 )	@ dst |= (aff2 >> rs1)
>  THUMB(	lsr	\mask, \rs2 )
>  THUMB(	orr	\dst, \mask )
> .endm

It _is_ nicer and probably faster in the cpu_resume path. Consider it applied.

Thank you very much,
Lorenzo