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

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Date:	Mon, 31 May 2010 02:55:16 -0700
From:	Arve Hjønnevåg <arve@...roid.com>
To:	markgross@...gnar.org
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Brian Swetland <swetland@...gle.com>,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	"Rafael J. Wysocki" <rjw@...k.pl>, mark.gross@...el.com
Subject: Re: [RFC] lp_events: an lternitive to suspend blocker user mode and 
	kernel API

On Sun, May 30, 2010 at 1:04 PM, mark gross <640e9920@...il.com> wrote:
> Low Power Events is a possible alternative to suspend blocker / wake
> lock API used by Android.
>
> It provides comparable power state notification and kernel mode critical
> section definition.  It differs from suspend blocker in that:
> 1) it is a platform and device independent implementation.  Device
> specific code is register as lp_ops, similar to pm_ops.  Drivers use
> the platform independent functions.
>
How is this more platform independent than suspend blockers?

> 2) it forces a user mode transition coming out of a LP state.
> Notification of wake up sources go to the user mode process managing the
> lp states.  Notification of blocked LP state entry is through an
> error return, and notification of un-blocking is through a file node as
> well.
>
If you want a user mode transition for every resume, you can easily
get this with the opportunistic suspend patchset by sending an input
event (or other a custom event with that blocks suspend) from a
driver's resume hook.

> I think the change need to the Google Android user mode power handling
> code can be limited to changes to _only_
> "hardware/libhardware_legacy/power/power.c"
>
> This code is still just a prototype of the platform independent code,
> and I'm implementing it on Eclair for the Intel Moorestown platform this
> weekend.  I'll have patches to eclair and updated kernel patches that
> enable this sometime Monday, after I bring it up on my target device.
> Hopefully by the end of next week I think I'll have it working well with
> Android.
>
> At this time the following patch is only known to compile.  I send it to
> help with the discussion.
>
> FWTW I do work on Android at Intel and I think I can make this work.
> (well, today I do.)
>
> --mgross
>
> Draft kernel patch :
>
...
> +
> +/dev/lpe_wake_event:
> +reads from this returns a list of wake events that happened between entry
> +into the LP state and the return from the read of the low_power_enter device
> +node.  User mode is expected to do something with these events before
> +re-trying to enter low power mode.
> +

I don't think this will work very well. Multiple input events can be
pending at the same time. If you register a single wake-event for an
input device, you don't know if all the events have been read when you
try to clear this wake-event.


-- 
Arve Hjønnevåg
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