Re: [PATCH v2] arm64: sleep: factor sleep_save_stash slot lookup into a macro

[Will Deacon]

On Fri, Jul 17, 2026 at 11:47:46AM +0000, Bradley Morgan wrote:
> Both __cpu_suspend_enter() and _cpu_resume() open code the same
> MPIDR_EL1 hash lookup to find the current CPU's slot in
> sleep_save_stash. Factor it into a get_sleep_stash_slot
> macro.
> 
> Since that macro would be the only remaining user of
> compute_mpidr_hash, inline the hash computation into
> get_sleep_stash_slot and just remove compute_mpidr_hash
> altogether.
> 
> No functional change intended.
> 
> Signed-off-by: Bradley Morgan <include@xxxxxxxxx>
> ---
> Changes since V1:
> - Inline the macro, there only is one user. (Will)
> - Also change the C psuedocode to be correct
> 
>  arch/arm64/kernel/sleep.S | 103 +++++++++++++++-----------------------
>  1 file changed, 41 insertions(+), 62 deletions(-)
> 
> diff --git a/arch/arm64/kernel/sleep.S b/arch/arm64/kernel/sleep.S
> index f093cdf71be1..dcf00a4d6233 100644
> --- a/arch/arm64/kernel/sleep.S
> +++ b/arch/arm64/kernel/sleep.S
> @@ -7,48 +7,48 @@
>  
>  	.text
>  /*
> - * Implementation of MPIDR_EL1 hash algorithm through shifting
> + * Compute the address of the current CPU's entry in sleep_save_stash,
> + * i.e. &sleep_save_stash[hash(MPIDR_EL1)], where the hash is an
> + * implementation of the MPIDR_EL1 hash algorithm through shifting
>   * and OR'ing.
>   *
> - * @dst: register containing hash result
> - * @rs0: register containing affinity level 0 bit shift
> - * @rs1: register containing affinity level 1 bit shift
> - * @rs2: register containing affinity level 2 bit shift
> - * @rs3: register containing affinity level 3 bit shift
> - * @mpidr: register containing MPIDR_EL1 value
> - * @mask: register containing MPIDR mask
> - *
>   * Pseudo C-code:
>   *
> - *u32 dst;
> + *	u64 mpidr = MPIDR_EL1 & mpidr_hash.mask;
> + *	u32 hash = ((mpidr & 0xff) >> mpidr_hash.shift_aff[0]) |
> + *		   ((mpidr & 0xff00) >> mpidr_hash.shift_aff[1]) |
> + *		   ((mpidr & 0xff0000) >> mpidr_hash.shift_aff[2]) |
> + *		   ((mpidr & 0xff00000000) >> mpidr_hash.shift_aff[3]);
> + *	slot = &sleep_save_stash[hash];
> + *
> + * @slot: output register
>   *
> - *compute_mpidr_hash(u32 rs0, u32 rs1, u32 rs2, u32 rs3, u64 mpidr, u64 mask) {
> - *	u32 aff0, aff1, aff2, aff3;
> - *	u64 mpidr_masked = mpidr & mask;
> - *	aff0 = mpidr_masked & 0xff;
> - *	aff1 = mpidr_masked & 0xff00;
> - *	aff2 = mpidr_masked & 0xff0000;
> - *	aff3 = mpidr_masked & 0xff00000000;
> - *	dst = (aff0 >> rs0 | aff1 >> rs1 | aff2 >> rs2 | aff3 >> rs3);
> - *}
> - * Input registers: rs0, rs1, rs2, rs3, mpidr, mask
> - * Output register: dst
> - * Note: input and output registers must be disjoint register sets
> -         (eg: a macro instance with mpidr = x1 and dst = x1 is invalid)
> + * Clobbers: x2 - x8
>   */
> -	.macro compute_mpidr_hash dst, rs0, rs1, rs2, rs3, mpidr, mask
> -	and	\mpidr, \mpidr, \mask		// mask out MPIDR bits
> -	and	\dst, \mpidr, #0xff		// mask=aff0
> -	lsr	\dst ,\dst, \rs0		// dst=aff0>>rs0
> -	and	\mask, \mpidr, #0xff00		// mask = aff1
> -	lsr	\mask ,\mask, \rs1
> -	orr	\dst, \dst, \mask		// dst|=(aff1>>rs1)
> -	and	\mask, \mpidr, #0xff0000	// mask = aff2
> -	lsr	\mask ,\mask, \rs2
> -	orr	\dst, \dst, \mask		// dst|=(aff2>>rs2)
> -	and	\mask, \mpidr, #0xff00000000	// mask = aff3
> -	lsr	\mask ,\mask, \rs3
> -	orr	\dst, \dst, \mask		// dst|=(aff3>>rs3)
> +	.macro get_sleep_stash_slot slot
> +	mrs	x3, mpidr_el1
> +	adr_l	x2, mpidr_hash
> +	ldr	x8, [x2, #MPIDR_HASH_MASK]
> +	/*
> +	 * Following code relies on the struct mpidr_hash
> +	 * members size.
> +	 */
> +	ldp	w4, w5, [x2, #MPIDR_HASH_SHIFTS]
> +	ldp	w6, w7, [x2, #(MPIDR_HASH_SHIFTS + 8)]
> +	and	x3, x3, x8			// mask out MPIDR bits
> +	and	x2, x3, #0xff			// aff0
> +	lsr	x2, x2, x4			// hash = aff0 >> rs0
> +	and	x8, x3, #0xff00			// aff1
> +	lsr	x8, x8, x5
> +	orr	x2, x2, x8			// hash |= aff1 >> rs1
> +	and	x8, x3, #0xff0000		// aff2
> +	lsr	x8, x8, x6
> +	orr	x2, x2, x8			// hash |= aff2 >> rs2
> +	and	x8, x3, #0xff00000000		// aff3
> +	lsr	x8, x8, x7
> +	orr	x2, x2, x8			// hash |= aff3 >> rs3
> +	ldr_l	\slot, sleep_save_stash
> +	add	\slot, \slot, x2, lsl #3	// slot = &sleep_save_stash[hash]

nit: In the old code, rs0-rs3 were arguments to the macro. Now that you've
removed those, the comments are stale.

Will