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

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Message-ID: <20160822134313.GJ14680@arm.com>
Date:   Mon, 22 Aug 2016 14:43:14 +0100
From:   Will Deacon <will.deacon@....com>
To:     Andy Gross <andy.gross@...aro.org>
Cc:     linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Stephen Boyd <sboyd@...eaurora.org>,
        stanimir.varbanov@...aro.org, linux-kernel@...r.kernel.org,
        patches@...aro.org, Bjorn Andersson <bjorn.andersson@...aro.org>,
        lorenzo.pieralisi@....com, sudeep.holla@....com
Subject: Re: [PATCH 1/2] arm64: kernel: Add SMC Session ID to results

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@...aro.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