linux-kernel - Re: [PATCH v3] power: add an API to log wakeup reasons

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Date:	Thu, 13 Mar 2014 17:43:20 -0700
From:	Ruchi Kandoi <kandoiruchi@...gle.com>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	Greg Hackmann <ghackmann@...gle.com>,
	John Stultz <john.stultz@...aro.org>,
	Todd Poynor <toddpoynor@...gle.com>
Subject: Re: [PATCH v3] power: add an API to log wakeup reasons

This should be true most of the times.

But there might be cases otherwise too.

For instance, there was a bug earlier with wi-fi which would cause the
system to wake up but not get hold of a wakeup source because there
wasn't any work for it to do. In that case, the wakeup sources would
not log such an event.

Additionally, there could be a situation where an IRQ caused the
system to resume from suspend. And since the system was up, a driver
could take a wakeup source. In this case we would assume that the
driver would have woken the system, but in reality the driver held the
wakeup source only because the system was up and did not cause the
wake up to happen.

Regards,
Ruchi Kandoi

On Thu, Mar 13, 2014 at 3:18 PM, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> Hi,
>
> I saw the v4, but I don't have it handy, so replying here.
>
> On Wednesday, March 12, 2014 12:46:38 PM Ruchi Kandoi wrote:
>> For power management diagnostic purposes, it is often useful to know
>> what interrupts are frequently waking the system from low power
>> suspend mode, especially on battery-powered consumer electronics
>> devices that are expected to spend much of their time in low-power
>> suspend while not in active use.  For example, reduced battery life on
>> a mobile phone may be caused in part by frequent wakeups by broadcast
>> traffic on a busy wireless LAN even while the screen is off and the
>> phone not in active use.
>>
>> Add API log_wakeup_reason() exposes it to userspace via the sysfs path
>> /sys/kernel/wakeup_reasons/last_resume_reason. This API would be called
>> from the paltform specific, or from the driver for the interrupt controller,
>> when the system resumes because of an IRQ. It logs the reasons which caused
>> the system to wakeup from the low-power mode.
>
> So what exactly is wrong with using wakeup sources for this purpose?
>
> --
> I speak only for myself.
> Rafael J. Wysocki, Intel Open Source Technology Center.
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