linux-kernel - Re: [linux-pm] suspend blockers & Android integration

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Message-ID: <AANLkTilrJYg-z6mbRfhhrDdhpWUYSXGQEMCGgBj24xZs@mail.gmail.com>
Date:	Wed, 9 Jun 2010 21:51:38 -0700
From:	Arve Hjønnevåg <arve@...roid.com>
To:	david@...g.hm
Cc:	Alan Stern <stern@...land.harvard.edu>, tytso@....edu,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Florian Mickler <florian@...kler.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Brian Swetland <swetland@...gle.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	LKML <linux-kernel@...r.kernel.org>, Neil Brown <neilb@...e.de>,
	James Bottomley <James.Bottomley@...e.de>,
	Linux PM <linux-pm@...ts.linux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Felipe Balbi <felipe.balbi@...ia.com>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [linux-pm] suspend blockers & Android integration

2010/6/9  <david@...g.hm>:
> On Wed, 9 Jun 2010, Arve Hj?nnev?g wrote:
>
>>
>> The power may not see the event, the process that reads the event will
>> always see it. If the power manager is not in the poll call when the
>> event happens, the process that reads the event can read the event
>> before the power manager calls poll.
>>
>
>>
>> All input events that can wake the system are handled by one
>> user-space suspend blocker. Input devices come and go so we would need
>> to add and remove the fds dynamically.
>
>
>>
>> For that to work the wakeup events would have to be reported to the
>> power manager in a reliable way in the first place. Passing the file
>> descriptor that the app uses to the power manager does not work for
>> this, since the app could read the event while the power manager was
>> not in the poll call and the power manager would never see it. Also,
>> existing apps don't pass their file descriptors to the power manager,
>> so it has the get the event from somewhere else.
>>
>
> why could the suspend blocker process see all events, but the power manager
> process not see the events?
>

Because in this proposal the power manager only looks for the events
(on the same queue) when no user space suspend blockers are active.

> have the userspace talk to the power manager the way it does to the suspend
> blocker now and what's the difference?
>
> effectivly think s/suspend blocker/power manager/ (with the power manager
> doing all the other things that are proposed instead of grabbing the
> wakelock), the difference should be hidden to the rest of userspace.
>
> what am I missing here?
>

The current user space interface does not require that clients
register the file descriptors that they get wakeup events from with
another process.

-- 
Arve Hjønnevåg
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