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

[Nicolas Pitre]

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


Nicolas