Re: [PATCH 1/2] arm64: kernel: Add SMC Session ID to results

Will Deacon
2016-08-22T13:43:50Z

On Sat, Aug 20, 2016 at 12:51:13AM -0500, Andy Gross wrote:
> This patch adds the SMC Session ID to the results passed back from SMC
> calls. The Qualcomm SMC implementation provides for interrupted SMC
> functions. When this occurs, the SMC call will return a session ID that
> is required to be used when resuming the interrupted SMC call.
>
> Signed-off-by: Andy Gross <andy.gross@linaro.org>
> ---
> arch/arm64/kernel/asm-offsets.c | 1 +
> arch/arm64/kernel/smccc-call.S | 1 +
> include/linux/arm-smccc.h | 4 +++-
> 3 files changed, 5 insertions(+), 1 deletion(-)

[...]

> diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h
> index b5abfda..82d919f 100644
> --- a/include/linux/arm-smccc.h
> +++ b/include/linux/arm-smccc.h
> @@ -63,18 +63,20 @@
> /**
> * struct arm_smccc_res - Result from SMC/HVC call
> * @a0-a3 result values from registers 0 to 3
> + * @a6 Session ID register (optional)
> */
> struct arm_smccc_res {
> unsigned long a0;
> unsigned long a1;
> unsigned long a2;
> unsigned long a3;
> + unsigned long a6;
> };
>
> /**
> * arm_smccc_smc() - make SMC calls
> * @a0-a7: arguments passed in registers 0 to 7
> - * @res: result values from registers 0 to 3
> + * @res: result values from registers 0 to 3 and optional register 6

AFAICT from reading the SMCCC spec, parameter register 6 is "Unpredictable,
Scratch registers" in return state, so I don't think this is correct.

What am I missing?

Will