linux-kernel - Re: [PATCH v5 3/5] x86, apic: Add freeze event support

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Date:   Thu, 13 Jul 2017 07:13:05 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Derek Basehore <dbasehore@...omium.org>
cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Rajneesh Bhardwaj <rajneesh.bhardwaj@...el.com>,
        x86@...nel.org, platform-driver-x86@...r.kernel.org,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Len Brown <len.brown@...el.com>, linux-pm@...r.kernel.org
Subject: Re: [PATCH v5 3/5] x86, apic: Add freeze event support

On Fri, 7 Jul 2017, Derek Basehore wrote:

> This adds support to the clock event devices created by apic to use
> freeze events. The apic is able to run a timer during freeze with near
> zero power impact on modern CPUs such as skylake. This will allow
> S0ix, suspend-to-idle, to be validated on Intel CPUs that support it.
> 
> This is needed because bugs with power settings on the SoC can prevent
> S0ix entry. There is also no way to check this before idling all of
> the CPUs.
> 
> Signed-off-by: Derek Basehore <dbasehore@...omium.org>
> ---
>  arch/x86/kernel/apic/apic.c | 24 +++++++++++++++++++++++-
>  1 file changed, 23 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
> index 98b3dd8cf2bf..adc69d2f11ce 100644
> --- a/arch/x86/kernel/apic/apic.c
> +++ b/arch/x86/kernel/apic/apic.c
> @@ -480,6 +480,26 @@ static int lapic_next_deadline(unsigned long delta,
>  	return 0;
>  }
>  
> +static int lapic_event_expired(struct clock_event_device *evt)

That want's to have a boolean return.

> +{
> +	u32 cct;
> +
> +	cct = apic_read(APIC_TMCCT);
> +	return cct == 0 ? 1 : 0;

which makes that:

      	return !cct;

> +}

Thanks,

	tglx