[PATCH 01/13] ARM: suspend: use hash of cpu_logical_map value to index into save array

[Dave Martin]

On Mon, Jul 22, 2013 at 11:31:17PM -0400, Nicolas Pitre wrote:
> Currently we hash the MPIDR of the CPU being suspended to determine which
> entry in the sleep_save_sp array to use. In some situations, such as when
> we want to resume on another physical CPU, the MPIDR of another CPU should
> be used instead.
> 
> So let's use the value of cpu_logical_map(smp_processor_id()) in place
> of the MPIDR in the suspend path.  This will result in the same index
> being used as with the previous code unless the caller has modified
> cpu_logical_map() beforehand.

This only works because we happen to swap MPIDRs in cpu_logical_map
before we get here, so that cpu_logical_map(smp_processor_id())
described the post-resume situation for this logical CPU, not the
current situation.

We have to swizzle cpu_logical_map() somewhere, and the suspend path is
just as good as the resume path for that.  But this patch commits us to
requiring that on the suspend path specifically -- I think that ought to
be mentioned somewhere.  A comment in the preamble for __cpu_suspend
would be enough, I think.

Looks like the patch should work though, and it does remove the need to
read the MPIDR, which is slightly nicer for the non-switcher case.

Cheers
---Dave

> 
> The register allocation in __cpu_suspend is reworked in order to better
> accommodate the additional argument.
> 
> Signed-off-by: Nicolas Pitre <nico at linaro.org>
> ---
>  arch/arm/kernel/sleep.S   | 25 +++++++++++--------------
>  arch/arm/kernel/suspend.c |  8 +++++---
>  2 files changed, 16 insertions(+), 17 deletions(-)
> 
> diff --git a/arch/arm/kernel/sleep.S b/arch/arm/kernel/sleep.S
> index db1536b8b3..836d10e698 100644
> --- a/arch/arm/kernel/sleep.S
> +++ b/arch/arm/kernel/sleep.S
> @@ -55,6 +55,7 @@
>   * specific registers and some other data for resume.
>   *  r0 = suspend function arg0
>   *  r1 = suspend function
> + *  r2 = MPIDR value used to index into sleep_save_sp
>   */
>  ENTRY(__cpu_suspend)
>  	stmfd	sp!, {r4 - r11, lr}
> @@ -67,23 +68,19 @@ ENTRY(__cpu_suspend)
>  	mov	r5, sp			@ current virtual SP
>  	add	r4, r4, #12		@ Space for pgd, virt sp, phys resume fn
>  	sub	sp, sp, r4		@ allocate CPU state on stack
> -	stmfd	sp!, {r0, r1}		@ save suspend func arg and pointer
> -	add	r0, sp, #8		@ save pointer to save block
> -	mov	r1, r4			@ size of save block
> -	mov	r2, r5			@ virtual SP
>  	ldr	r3, =sleep_save_sp
> +	stmfd	sp!, {r0, r1}		@ save suspend func arg and pointer
>  	ldr	r3, [r3, #SLEEP_SAVE_SP_VIRT]
> -	ALT_SMP(mrc p15, 0, r9, c0, c0, 5)
> -        ALT_UP_B(1f)
> -	ldr	r8, =mpidr_hash
> -	/*
> -	 * This ldmia relies on the memory layout of the mpidr_hash
> -	 * struct mpidr_hash.
> -	 */
> -	ldmia	r8, {r4-r7}	@ r4 = mpidr mask (r5,r6,r7) = l[0,1,2] shifts
> -	compute_mpidr_hash	lr, r5, r6, r7, r9, r4
> -	add	r3, r3, lr, lsl #2
> +	ALT_SMP(ldr r0, =mpidr_hash)
> +       ALT_UP_B(1f)
> +	/* This ldmia relies on the memory layout of the mpidr_hash struct */
> +	ldmia	r0, {r1, r6-r8}	@ r1 = mpidr mask (r6,r7,r8) = l[0,1,2] shifts
> +	compute_mpidr_hash	r0, r6, r7, r8, r2, r1
> +	add	r3, r3, r0, lsl #2
>  1:
> +	mov	r2, r5			@ virtual SP
> +	mov	r1, r4			@ size of save block
> +	add	r0, sp, #8		@ pointer to save block
>  	bl	__cpu_suspend_save
>  	adr	lr, BSYM(cpu_suspend_abort)
>  	ldmfd	sp!, {r0, pc}		@ call suspend fn
> diff --git a/arch/arm/kernel/suspend.c b/arch/arm/kernel/suspend.c
> index 41cf3cbf75..2835d35234 100644
> --- a/arch/arm/kernel/suspend.c
> +++ b/arch/arm/kernel/suspend.c
> @@ -10,7 +10,7 @@
>  #include <asm/suspend.h>
>  #include <asm/tlbflush.h>
>  
> -extern int __cpu_suspend(unsigned long, int (*)(unsigned long));
> +extern int __cpu_suspend(unsigned long, int (*)(unsigned long), u32 cpuid);
>  extern void cpu_resume_mmu(void);
>  
>  #ifdef CONFIG_MMU
> @@ -21,6 +21,7 @@ extern void cpu_resume_mmu(void);
>  int cpu_suspend(unsigned long arg, int (*fn)(unsigned long))
>  {
>  	struct mm_struct *mm = current->active_mm;
> +	u32 __mpidr = cpu_logical_map(smp_processor_id());
>  	int ret;
>  
>  	if (!idmap_pgd)
> @@ -32,7 +33,7 @@ int cpu_suspend(unsigned long arg, int (*fn)(unsigned long))
>  	 * resume (indicated by a zero return code), we need to switch
>  	 * back to the correct page tables.
>  	 */
> -	ret = __cpu_suspend(arg, fn);
> +	ret = __cpu_suspend(arg, fn, __mpidr);
>  	if (ret == 0) {
>  		cpu_switch_mm(mm->pgd, mm);
>  		local_flush_bp_all();
> @@ -44,7 +45,8 @@ int cpu_suspend(unsigned long arg, int (*fn)(unsigned long))
>  #else
>  int cpu_suspend(unsigned long arg, int (*fn)(unsigned long))
>  {
> -	return __cpu_suspend(arg, fn);
> +	u32 __mpidr = cpu_logical_map(smp_processor_id());
> +	return __cpu_suspend(arg, fn, __mpidr);
>  }
>  #define	idmap_pgd	NULL
>  #endif
> -- 
> 1.8.1.2
>