linux-kernel - Re: A desktop environment[1] kernel wishlist

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Date:	Tue, 5 May 2015 13:58:12 -0700
From:	Chirantan Ekbote <chirantan@...omium.org>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	John Stultz <john.stultz@...aro.org>,
	Olof Johansson <olof@...om.net>,
	Bastien Nocera <hadess@...ess.net>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	snanda@...omium.org, Tomeu Vizoso <tomeu.vizoso@...labora.com>,
	Linux PM list <linux-pm@...r.kernel.org>
Subject: Re: A desktop environment[1] kernel wishlist

On Tue, May 5, 2015 at 12:35 PM, Alan Stern <stern@...land.harvard.edu> wrote:
> On Tue, 5 May 2015, Chirantan Ekbote wrote:
>
>> This is our plan for the next version (see my email earlier in this
>> thread).  Keeping a hybrid power state with hacks in the drivers isn't
>> really maintainable, scalable, or upstream-able and has caused us some
>> headaches already.  Unfortunately we were working with the 3.14 kernel
>> at the time, which didn't have the framework necessary to do anything
>> else.  The new version of lucid sleep will have the power manager
>> runtime suspend power-hungry devices before a suspend so that they
>> remain powered off at resume time.  The power manager can then decide
>> to resume those devices based on whether the wakeup event was
>> user-triggered.
>>
>> Being able to determine the wakeup type from userspace is the only
>> functionality we need from the kernel that doesn't already exist in
>> mainline.
>
> Maybe you can simplify the problem.  You don't really need to know the
> wakeup type, or to determine which device was responsible for the
> wakeup.  All you really need to know is whether the wakeup was
> user-triggered.  That may be much easier to discover.
>

You are, of course, correct.  Ultimately the only requirement we have
is that there exists a way for userspace to determine if the system
woke up because of a user-triggered event.  The actual mechanism by
which this determination is made isn't something I feel strongly
about.  The reason I had been focusing on exposing the actual wakeup
event to userspace is because classifying wakeup events as
user-triggered or not feels to me like a policy decision that should
be left to userspace.  If the kernel maintainers are ok with doing
this work in the kernel instead and only exposing a binary yes/no bit
to userspace for user-triggered wakeups, that's perfectly fine because
it still meets our requirements.

> Alan Stern
>
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