linux-kernel - Re: [PATCH v5 2/5] tick: Add freeze timer events

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Message-ID: <20170713073200.uh3oxqowei6vxvwy@hirez.programming.kicks-ass.net>
Date:   Thu, 13 Jul 2017 09:32:00 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Derek Basehore <dbasehore@...omium.org>
Cc:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        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 2/5] tick: Add freeze timer events

On Fri, Jul 07, 2017 at 05:03:00PM -0700, Derek Basehore wrote:
> Adds a new feature to tick to schedule wakeups on a CPU during freeze.
> This won't fully wake up the system (devices are not resumed), but
> allow simple platform functionality to be run during freeze with
> little power impact.
> 
> This implementation allows an idle driver to setup a timer event with
> the clock event device when entering freeze by calling
> tick_set_freeze_event. Only one caller should exist for the function.
> 
> tick_freeze_event_expired is used to check if the timer went off when
> the CPU wakes.
> 
> The event is cleared by tick_clear_freeze_event.

Why? What's wrong with using the RTC stuff? RTC should be able to wake
suspended systems, see RTCWAKE(8).