linux-kernel - Re: [PATCH v6 08/10] arm/arm64: Provide a wrapper for SMCCC 1.1 calls

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Date:   Mon, 21 Oct 2019 12:42:57 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Steven Price <steven.price@....com>
Cc:     Will Deacon <will@...nel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <kvmarm@...ts.cs.columbia.edu>,
        Catalin Marinas <catalin.marinas@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář 
        <rkrcmar@...hat.com>, Russell King <linux@...linux.org.uk>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Pouloze <suzuki.poulose@....com>,
        Mark Rutland <mark.rutland@....com>, <kvm@...r.kernel.org>,
        <linux-doc@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 08/10] arm/arm64: Provide a wrapper for SMCCC 1.1 calls

On 2019-10-11 13:59, Steven Price wrote:
> SMCCC 1.1 calls may use either HVC or SMC depending on the PSCI
> conduit. Rather than coding this in every call site provide a macro
> which uses the correct instruction. The macro also handles the case
> where no PSCI conduit is configured returning a not supported error
> in res, along with returning the conduit used for the call.
>
> This allow us to remove some duplicated code and will be useful later
> when adding paravirtualized time hypervisor calls.
>
> Signed-off-by: Steven Price <steven.price@....com>
> Acked-by: Will Deacon <will@...nel.org>
> ---
>  include/linux/arm-smccc.h | 44 
> +++++++++++++++++++++++++++++++++++++++
>  1 file changed, 44 insertions(+)
>
> diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h
> index 5daf0e2adf47..fd84a9bfb455 100644
> --- a/include/linux/arm-smccc.h
> +++ b/include/linux/arm-smccc.h
> @@ -303,6 +303,50 @@ asmlinkage void __arm_smccc_hvc(unsigned long
> a0, unsigned long a1,
>  #define SMCCC_RET_NOT_SUPPORTED			-1
>  #define SMCCC_RET_NOT_REQUIRED			-2
>
> +/* Like arm_smccc_1_1* but always returns SMCCC_RET_NOT_SUPPORTED.
> + * Used when the PSCI conduit is not defined. The empty asm 
> statement
> + * avoids compiler warnings about unused variables.

nit: comment style.

> + */
> +#define __fail_smccc_1_1(...)						\
> +	do {								\
> +		__declare_args(__count_args(__VA_ARGS__), __VA_ARGS__);	\
> +		asm ("" __constraints(__count_args(__VA_ARGS__)));	\
> +		if (___res)						\
> +			___res->a0 = SMCCC_RET_NOT_SUPPORTED;		\
> +	} while (0)
> +
> +/*
> + * arm_smccc_1_1_invoke() - make an SMCCC v1.1 compliant call
> + *
> + * This is a variadic macro taking one to eight source arguments, 
> and
> + * an optional return structure.
> + *
> + * @a0-a7: arguments passed in registers 0 to 7
> + * @res: result values from registers 0 to 3
> + *
> + * This macro will make either an HVC call or an SMC call depending 
> on the
> + * current PSCI conduit. If no valid conduit is available then -1
> + * (SMCCC_RET_NOT_SUPPORTED) is returned in @res.a0 (if supplied).
> + *
> + * The return value also provides the conduit that was used.
> + */
> +#define arm_smccc_1_1_invoke(...) ({					\
> +		int method = psci_ops.conduit;				\
> +		switch (method) {					\
> +		case PSCI_CONDUIT_HVC:					\
> +			arm_smccc_1_1_hvc(__VA_ARGS__);			\
> +			break;						\
> +		case PSCI_CONDUIT_SMC:					\
> +			arm_smccc_1_1_smc(__VA_ARGS__);			\
> +			break;						\
> +		default:						\
> +			__fail_smccc_1_1(__VA_ARGS__);			\
> +			method = PSCI_CONDUIT_NONE;			\
> +			break;						\
> +		}							\
> +		method;							\
> +	})
> +
>  /* Paravirtualised time calls (defined by ARM DEN0057A) */
>  #define ARM_SMCCC_HV_PV_TIME_FEATURES				\
>  	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,			\

All this should most probably go on top of the SMCCC conduit cleanup 
that
has already been already queued in the arm64 tree (see 
arm64/for-next/smccc-conduit-cleanup).

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...