linux-kernel - Re: [PATCH 1/2] drivers: firmware: psci: Add psci_is

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Date:   Thu, 12 Oct 2017 08:58:42 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Jisheng Zhang <Jisheng.Zhang@...aptics.com>
Cc:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Mark Rutland <mark.rutland@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/2] drivers: firmware: psci: Add psci_is_available()

Hi Jisheng,

On Thu, Oct 12, 2017 at 4:58 AM, Jisheng Zhang
<Jisheng.Zhang@...aptics.com> wrote:
> On Wed, 11 Oct 2017 10:03:01 +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.
>>
>> 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.
>
> the psci_ops is a global var, why not check psci_ops.mmnn members
> individually in each drivers? check IS_ENABLED(CONFIG_ARM_PSCI_FW) for
> building time ennoblement.

While psci_ops is a global var, it only exists if CONFIG_ARM_PSCI_FW=y,
so typical code like

    if (IS_ENABLED(CONFIG_ARM_PSCI_FW) && psci_ops.cpu_suspend) {
            ...
    }

won't link. So having a helper is useful.
The alternative is #ifdef.

>> 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;
>
> IIRC, for PSCI 0.1, cpu_suspend is optional, we can't say the PSCI isn't
> available if cpu_suspend is missing.

Hmm...

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds