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Date:   Wed, 25 Oct 2017 16:45:37 +0100
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Geert Uytterhoeven <geert+renesas@...der.be>
Cc:     Mark Rutland <mark.rutland@....com>,
        linux-renesas-soc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [1/2] drivers: firmware: psci: Add psci_is_available()

On Wed, Oct 11, 2017 at 10:03:01AM +0200, Geert Uytterhoeven wrote:
> PSCI support may be disabled at build time (by configuration) or at
> run-time (PSCI firmware not present).  While CONFIG_ARM_PSCI_FW can be
> used to check for build time enablement, there is currently no simple
> way to check if PSCI is actually available and used.
> 
> Hence add a helper function to check if PSCI is available.

Hi Geert,

excuse us the delay in responding. I think it would be better if the
check just carries out a DT/ACPI matching check rather than being based
on PSCI ops initialization but before doing that I would like first to
understand what this function can be actually used for (ie I do not
think the usage in the PSCI checker is relevant to this discussion).

Thanks,
Lorenzo

> This is useful for e.g. drivers that are used on platforms with and
> without PSCI.  Such drivers may need to take provisions for proper
> operation when PSCI is used, and/or to implement functionality that is
> usually provided by PSCI.
> 
> Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
> ---
>  drivers/firmware/psci.c | 5 +++++
>  include/linux/psci.h    | 2 ++
>  2 files changed, 7 insertions(+)
> 
> diff --git a/drivers/firmware/psci.c b/drivers/firmware/psci.c
> index da469c972b503f83..a3a11e2d8ffffaaa 100644
> --- a/drivers/firmware/psci.c
> +++ b/drivers/firmware/psci.c
> @@ -670,6 +670,11 @@ int __init psci_dt_init(void)
>  	return init_fn(np);
>  }
>  
> +bool psci_is_available(void)
> +{
> +	return psci_ops.cpu_off && psci_ops.cpu_on && psci_ops.cpu_suspend;
> +}
> +
>  #ifdef CONFIG_ACPI
>  /*
>   * We use PSCI 0.2+ when ACPI is deployed on ARM64 and it's
> diff --git a/include/linux/psci.h b/include/linux/psci.h
> index bdea1cb5e1db142b..2bdee325aeb80cf6 100644
> --- a/include/linux/psci.h
> +++ b/include/linux/psci.h
> @@ -39,8 +39,10 @@ extern struct psci_operations psci_ops;
>  
>  #if defined(CONFIG_ARM_PSCI_FW)
>  int __init psci_dt_init(void);
> +bool psci_is_available(void);
>  #else
>  static inline int psci_dt_init(void) { return 0; }
> +static inline bool psci_is_available(void) { return false; }
>  #endif
>  
>  #if defined(CONFIG_ARM_PSCI_FW) && defined(CONFIG_ACPI)

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