[U-Boot] [PATCH] arm: psci: save and restore registers from r4 to r12

[C.H. Zhao]

________________________________
From: Chen-Yu Tsai <wens at csie.org>
Sent: Thursday, October 13, 2016 5:52 PM
To: C.H. Zhao
Cc: U-Boot Mailing List; Albert ARIBAUD; z.chenhui at gmail.com
Subject: Re: [U-Boot] [PATCH] arm: psci: save and restore registers from r4 to r12

On Sat, Oct 8, 2016 at 7:08 PM, Chenhui Zhao <chenhui.zhao at nxp.com> wrote:
> Save and restore core registers from r4 to r12 so that PSCI code won't
> break their value.
>
> Signed-off-by: Chenhui Zhao <chenhui.zhao at nxp.com>
> Signed-off-by: Alison Wang <alison.wang at nxp.com>
> Signed-off-by: Abhimanyu Saini <abhimanyu.saini at nxp.com>
> ---
>  arch/arm/cpu/armv7/psci.S | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm/cpu/armv7/psci.S b/arch/arm/cpu/armv7/psci.S
> index 6a36208..746297c 100644
> --- a/arch/arm/cpu/armv7/psci.S
> +++ b/arch/arm/cpu/armv7/psci.S
> @@ -152,7 +152,7 @@ _psci_table:
>         .word   0
>
>  _smc_psci:
> -       push    {r4-r7,lr}
> +       push    {r4-r12,lr}

This change is not needed. This function only uses r4-r7.
Any subroutines called should save variable registers (r4-r12)
themselves, per the ARM calling conventions.

ChenYu


[Chenhui] I do not think it is a normal calling, instead it is an exception handler. In the exception context,
it is necessary to save/restore all registers.

>
>         @ Switch to secure
>         mrc     p15, 0, r7, c1, c1, 0
> @@ -175,7 +175,7 @@ _smc_psci:
>         @ Switch back to non-secure
>  2:     mcr     p15, 0, r7, c1, c1, 0
>
> -       pop     {r4-r7, lr}
> +       pop     {r4-r12, lr}
>         movs    pc, lr                  @ Return to the kernel
>
>  @ Requires dense and single-cluster CPU ID space
> --
> 1.9.1
>
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