From: Arve Hjønnevåg on
On Sun, May 30, 2010 at 1:04 PM, mark gross <640e9920(a)> 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 Hj�nnev�g
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