Re: [Xen-devel] [[PATCH v3] 4/4] xen/arm: Replace call_smc with arm_smccc_smc

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 01/10/18 13:46, Julien Grall wrote:
> call_smc is a subset of arm_smccc_smc. Rather than having 2 methods to
> do SMCCC call, replace all call to the former by the later.
>
> Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
>
> ---
>
>     Changes in v3:
>         - Use PSCI_RET where needed
> ---
>  xen/arch/arm/Makefile            |  1 -
>  xen/arch/arm/platforms/exynos5.c |  3 ++-
>  xen/arch/arm/platforms/seattle.c |  4 ++--
>  xen/arch/arm/psci.c              | 37 +++++++++++++++++++++++++------------
>  xen/arch/arm/smc.S               | 21 ---------------------
>  xen/include/asm-arm/processor.h  |  3 ---
>  6 files changed, 29 insertions(+), 40 deletions(-)
>  delete mode 100644 xen/arch/arm/smc.S
>
> diff --git a/xen/arch/arm/Makefile b/xen/arch/arm/Makefile
> index b9b141dc84..37fa8268b3 100644
> --- a/xen/arch/arm/Makefile
> +++ b/xen/arch/arm/Makefile
> @@ -39,7 +39,6 @@ obj-y += processor.o
>  obj-y += psci.o
>  obj-y += setup.o
>  obj-y += shutdown.o
> -obj-y += smc.o
>  obj-y += smp.o
>  obj-y += smpboot.o
>  obj-y += sysctl.o
> diff --git a/xen/arch/arm/platforms/exynos5.c 
> b/xen/arch/arm/platforms/exynos5.c
> index c15ecf80f5..e2c0b7b878 100644
> --- a/xen/arch/arm/platforms/exynos5.c
> +++ b/xen/arch/arm/platforms/exynos5.c
> @@ -26,6 +26,7 @@
>  #include <asm/platforms/exynos5.h>
>  #include <asm/platform.h>
>  #include <asm/io.h>
> +#include <asm/smccc.h>
>  
>  static bool secure_firmware;
>  
> @@ -249,7 +250,7 @@ static int exynos5_cpu_up(int cpu)
>      iounmap(power);
>  
>      if ( secure_firmware )
> -        call_smc(SMC_CMD_CPU1BOOT, cpu, 0, 0);
> +        arm_smccc_smc(SMC_CMD_CPU1BOOT, cpu, NULL);
>  
>      return cpu_up_send_sgi(cpu);
>  }
> diff --git a/xen/arch/arm/platforms/seattle.c 
> b/xen/arch/arm/platforms/seattle.c
> index 893cc17972..64cc1868c2 100644
> --- a/xen/arch/arm/platforms/seattle.c
> +++ b/xen/arch/arm/platforms/seattle.c
> @@ -33,12 +33,12 @@ static const char * const seattle_dt_compat[] __initconst 
> =
>   */
>  static void seattle_system_reset(void)
>  {
> -    call_smc(PSCI_0_2_FN32_SYSTEM_RESET, 0, 0, 0);
> +    arm_smccc_smc(PSCI_0_2_FN32_SYSTEM_RESET, NULL);
>  }
>  
>  static void seattle_system_off(void)
>  {
> -    call_smc(PSCI_0_2_FN32_SYSTEM_OFF, 0, 0, 0);
> +    arm_smccc_smc(PSCI_0_2_FN32_SYSTEM_OFF, NULL);
>  }
>  
>  PLATFORM_START(seattle, "SEATTLE")
> diff --git a/xen/arch/arm/psci.c b/xen/arch/arm/psci.c
> index 941eec921b..4ae6504f3e 100644
> --- a/xen/arch/arm/psci.c
> +++ b/xen/arch/arm/psci.c
> @@ -42,42 +42,53 @@ uint32_t smccc_ver;
>  
>  static uint32_t psci_cpu_on_nr;
>  
> +#define PSCI_RET(res)   ((int32_t)(res).a0)
> +
>  int call_psci_cpu_on(int cpu)
>  {
> -    return call_smc(psci_cpu_on_nr, cpu_logical_map(cpu), 
> __pa(init_secondary), 0);
> +    struct arm_smccc_res res;
> +
> +    arm_smccc_smc(psci_cpu_on_nr, cpu_logical_map(cpu), __pa(init_secondary),
> +                  &res);
> +
> +    return PSCI_RET(res.a0);
>  }

Sorry if I'm jumping into the middle of a conversation, but why force
all callers to manually extract the return value when it is a fixed
register?

Wouldn't it be far easier to do this:

#define arcm_smccc_smc(...)                         \
    ({                                              \
        struct arm_smccc_res res;                   \
                                                    \
        if ( cpus_have_const_cap(ARM_SMCCC_1_1) )   \
            res = arm_smccc_1_1_smc(__VA_ARGS__);   \
        else                                        \
            res = arm_smccc_1_0_smc(__VA_ARGS__);   \
                                                    \
        (int)res.a0;                                \
    })

Which also allows the compiler to optimise out the structure if it isn't
read, and also avoids the caller needing to pass a NULL pointer for "I
don't want the result".

~Andrew

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