linux-kernel - Re: [linux-pm] [PATCH 8/9] Input: Block suspend while event queue is not empty.

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Message-Id: <201004250430.31054.rjw@sisk.pl>
Date:	Sun, 25 Apr 2010 04:30:30 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Arve Hjønnevåg <arve@...roid.com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	Márton Németh <nm127@...email.hu>,
	Thadeu Lima de Souza Cascardo <cascardo@...oscopio.com>,
	linux-input@...r.kernel.org, Sven Neumann <s.neumann@...mfeld.com>,
	linux-kernel@...r.kernel.org, Henrik Rydberg <rydberg@...omail.se>,
	Jiri Kosina <jkosina@...e.cz>,
	linux-pm@...ts.linux-foundation.org,
	Tero Saarni <tero.saarni@...il.com>,
	Matthew Garrett <mjg@...hat.com>
Subject: Re: [linux-pm] [PATCH 8/9] Input: Block suspend while event queue is not empty.

On Saturday 24 April 2010, Alan Stern wrote:
> On Fri, 23 Apr 2010, Arve Hjønnevåg wrote:
> 
> > On Fri, Apr 23, 2010 at 2:08 PM, Dmitry Torokhov
> > <dmitry.torokhov@...il.com> wrote:
> > > On Friday 23 April 2010 01:56:25 pm Randy Dunlap wrote:
> > >> On Thu, 22 Apr 2010 18:08:57 -0700 Arve Hjønnevåg wrote:
> > >> > Add an ioctl, EVIOCSSUSPENDBLOCK, to enable a suspend_blocker that will
> > >> > block suspend while the event queue is not empty. This allows userspace
> > >> > code to process input events while the device appears to be asleep.
> > >>
> > >> All new ioctls need to be added to Documentation/ioctl/ioctl-number.txt,
> > >> please.
> > >
> > > I do not see the reason for it to be in the kernel still. Have a process
> > > that listens to all input devices (or subset of them), once events stop
> > > coming initiate suspend.

This solution is not practical with the Android user space AFAICT.
 
> > I think the document added by the first patch explains this. The
> > solution you propose above will ignore a wakeup key pressed right
> > after user space decides to initiate suspend.
> 
> Is there some reason why this feature needs to be enabled by an 
> ioctl?  Why not make this suspend blocker permanently enabled?

The ioctl is there so that user space can use suspend blockers, which is
needed because only user space know that some activities are going to continue
and therefore the system should not be suspended (like playing music "in the
background").

>From all of the interfaces that could be used for this purpose ioctl appears to
be the most convenient (we need something that is per process and allows us
to carry out four operations: creat, destroy, activate, deactivate).

Rafael
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