[v2,21/29] ARM: kernel: use PC relative symbol references in suspend/resume code
diff mbox

Message ID 20170903120757.14968-22-ard.biesheuvel@linaro.org
State New
Headers show

Commit Message

Ard Biesheuvel Sept. 3, 2017, 12:07 p.m. UTC
Replace some unnecessary absolute references with relative ones. Also,
to prepare for runtime relocation, which occurs with the caches on,
defer taking the absolute address of cpu_resume_after_mmu() until after
the MMU is enabled.

Cc: Russell King <linux@armlinux.org.uk>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
 arch/arm/kernel/sleep.S | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

Comments

Nicolas Pitre Sept. 4, 2017, 6:24 p.m. UTC | #1
On Sun, 3 Sep 2017, Ard Biesheuvel wrote:

> Replace some unnecessary absolute references with relative ones. Also,
> to prepare for runtime relocation, which occurs with the caches on,
> defer taking the absolute address of cpu_resume_after_mmu() until after
> the MMU is enabled.
> 
> Cc: Russell King <linux@armlinux.org.uk>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

What's the point of that last hunk? I understand you load the address 
after the mMU is on. But you should be coming back from a sleep and 
caches ought to be clean at that point. Not that it is a bad thing to do 
but I don't understand your reason for it.


> ---
>  arch/arm/kernel/sleep.S | 9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm/kernel/sleep.S b/arch/arm/kernel/sleep.S
> index f4920b5d0fc4..5b02744f2f12 100644
> --- a/arch/arm/kernel/sleep.S
> +++ b/arch/arm/kernel/sleep.S
> @@ -60,15 +60,14 @@
>  ENTRY(__cpu_suspend)
>  	stmfd	sp!, {r4 - r11, lr}
>  #ifdef MULTI_CPU
> -	ldr	r10, =processor
> -	ldr	r4, [r10, #CPU_SLEEP_SIZE] @ size of CPU sleep state
> +	ldr_l	r4, processor + CPU_SLEEP_SIZE	@ size of CPU sleep state
>  #else
> -	ldr	r4, =cpu_suspend_size
> +	adr_l	r4, cpu_suspend_size
>  #endif
>  	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
> -	ldr	r3, =sleep_save_sp
> +	adr_l	r3, sleep_save_sp
>  	stmfd	sp!, {r0, r1}		@ save suspend func arg and pointer
>  	ldr	r3, [r3, #SLEEP_SAVE_SP_VIRT]
>  	ALT_SMP(W(nop))			@ don't use adr_l inside ALT_SMP()
> @@ -101,13 +100,13 @@ ENDPROC(cpu_suspend_abort)
>  	.align	5
>  	.pushsection	.idmap.text,"ax"
>  ENTRY(cpu_resume_mmu)
> -	ldr	r3, =cpu_resume_after_mmu
>  	instr_sync
>  	mcr	p15, 0, r0, c1, c0, 0	@ turn on MMU, I-cache, etc
>  	mrc	p15, 0, r0, c0, c0, 0	@ read id reg
>  	instr_sync
>  	mov	r0, r0
>  	mov	r0, r0
> +	ldr	r3, =cpu_resume_after_mmu
>  	ret	r3			@ jump to virtual address
>  ENDPROC(cpu_resume_mmu)
>  	.popsection
> -- 
> 2.11.0
> 
>
Ard Biesheuvel Sept. 4, 2017, 7:17 p.m. UTC | #2
On 4 September 2017 at 19:24, Nicolas Pitre <nicolas.pitre@linaro.org> wrote:
> On Sun, 3 Sep 2017, Ard Biesheuvel wrote:
>
>> Replace some unnecessary absolute references with relative ones. Also,
>> to prepare for runtime relocation, which occurs with the caches on,
>> defer taking the absolute address of cpu_resume_after_mmu() until after
>> the MMU is enabled.
>>
>> Cc: Russell King <linux@armlinux.org.uk>
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>
> What's the point of that last hunk? I understand you load the address
> after the mMU is on. But you should be coming back from a sleep and
> caches ought to be clean at that point. Not that it is a bad thing to do
> but I don't understand your reason for it.
>

I simply attempted to eliminate all uses of relocated quantities with
the caches off, but you are correct that this is only necessary for
boot and not for suspend/resume. This is actually somewhat of a
relief, since there is so much SOC specific suspend/resume code under
arch/arm, and the boot code is mostly shared.

Patch
diff mbox

diff --git a/arch/arm/kernel/sleep.S b/arch/arm/kernel/sleep.S
index f4920b5d0fc4..5b02744f2f12 100644
--- a/arch/arm/kernel/sleep.S
+++ b/arch/arm/kernel/sleep.S
@@ -60,15 +60,14 @@ 
 ENTRY(__cpu_suspend)
 	stmfd	sp!, {r4 - r11, lr}
 #ifdef MULTI_CPU
-	ldr	r10, =processor
-	ldr	r4, [r10, #CPU_SLEEP_SIZE] @ size of CPU sleep state
+	ldr_l	r4, processor + CPU_SLEEP_SIZE	@ size of CPU sleep state
 #else
-	ldr	r4, =cpu_suspend_size
+	adr_l	r4, cpu_suspend_size
 #endif
 	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
-	ldr	r3, =sleep_save_sp
+	adr_l	r3, sleep_save_sp
 	stmfd	sp!, {r0, r1}		@ save suspend func arg and pointer
 	ldr	r3, [r3, #SLEEP_SAVE_SP_VIRT]
 	ALT_SMP(W(nop))			@ don't use adr_l inside ALT_SMP()
@@ -101,13 +100,13 @@  ENDPROC(cpu_suspend_abort)
 	.align	5
 	.pushsection	.idmap.text,"ax"
 ENTRY(cpu_resume_mmu)
-	ldr	r3, =cpu_resume_after_mmu
 	instr_sync
 	mcr	p15, 0, r0, c1, c0, 0	@ turn on MMU, I-cache, etc
 	mrc	p15, 0, r0, c0, c0, 0	@ read id reg
 	instr_sync
 	mov	r0, r0
 	mov	r0, r0
+	ldr	r3, =cpu_resume_after_mmu
 	ret	r3			@ jump to virtual address
 ENDPROC(cpu_resume_mmu)
 	.popsection