linux-kernel - Re: [linux-pm] [RFC] lp_events: an lternitive to suspend blocker user mode and kernel API

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Date:	Tue, 1 Jun 2010 20:10:15 -0700
From:	Arve Hjønnevåg <arve@...roid.com>
To:	markgross@...gnar.org
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>, mark.gross@...el.com,
	Neil Brown <neilb@...e.de>,
	Brian Swetland <swetland@...gle.com>,
	linux-kernel@...r.kernel.org, Arve@...p1.linux-foundation.org,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-pm@...ts.linux-foundation.org,
	Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [linux-pm] [RFC] lp_events: an lternitive to suspend blocker user 
	mode and kernel API

2010/6/1 mark gross <640e9920@...il.com>:
> On Mon, May 31, 2010 at 10:24:30PM -0700, Arve Hjønnevåg wrote:
>> On Mon, May 31, 2010 at 10:09 PM, mark gross <640e9920@...il.com> wrote:
>> > On Tue, Jun 01, 2010 at 12:45:21AM +0200, Rafael J. Wysocki wrote:
>> >> On Tuesday 01 June 2010, mark gross wrote:
>> >> > On Mon, May 31, 2010 at 09:57:53AM +1000, Neil Brown wrote:
>> >> ...
>> >> > > So I would suggest modifying your proposal to simply create a new 'input'
>> >> > > device.  Any driver that supports wake-from-suspend queues an event to that
>> >> > > device when a wakeup event occurs.  If the device is open and has any queued
>> >> > > events, then a suspend request such as 'echo mem > /sys/power/state' completes
>> >> > > without going into full suspend.
>> >> >
>> >> > /me likes.
>> >> >
>> >> > > Then you just need to convince us that this mechanism can be used without any
>> >> > > race problems.  If it can, then it would certainly be a simple and
>> >> > > unobtrusive approach.
>> >> >
>> >> > Lets find out.
>> >>
>> >> Simple question: how is that better than the Alan Stern's proposed approach?
>> >>
>> > I just saw Alan Stern's proposal, and have gotten some input form some
>> > others.  I can't say my patch represents a better Idea than what Alan
>> > proposed.  However; what Alan (and Thomas) are talking about is
>> > effectively the same as the kenrel mode wakelock/suspend blocker thing,
>> > and although it reuses existing infrastructure, it doesn't solve the
>> > problem of needing overlapping blocking sections of code from ISR to
>> > user mode.
>> >
>>
>> I don't think your solution solves this either.
>
> Why?  my proposal effectively removes the overlapping kernel blocking
> sections uppon wake up by forcing the user mode to ack the wake event
> and re-issue the suspend request explicitly.  That pretty much solves
> that problem.
>

How to you ack the wakeup event in a safe way. Another wakeup event
can come in after you decided to ack the last event. Also when the
user-space power manager reads that there was a wakeup event, how does
it know if the real event has been delivered to user-space, and if the
user-space code that consumed this event has had a chance to block
suspend?

> We can talk about whether or not it can be used effectively with Android
> user mode PM or not, which I still think it can, but I need to try the
> mods to power.c.
>


-- 
Arve Hjønnevåg
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