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

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Date:	Fri, 31 Oct 2014 14:59:50 +0100
From:	Bastien Nocera <hadess@...ess.net>
To:	Pavel Machek <pavel@....cz>
Cc:	Theodore Ts'o <tytso@....edu>,
	Andy Lutomirski <luto@...capital.net>,
	John Stultz <john.stultz@...aro.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: A desktop environment[1] kernel wishlist

On Thu, 2014-10-30 at 18:41 +0100, Pavel Machek wrote:
> On Thu 2014-10-30 16:15:15, Bastien Nocera wrote:
> > On Thu, 2014-10-30 at 11:05 -0400, Theodore Ts'o wrote:
> > > On Thu, Oct 30, 2014 at 03:45:02PM +0100, Bastien Nocera wrote:
> > > > > Actually Maemo people (on Nokia N900 and friends) got it right: unlike
> > > > > android devices, it does not suspend to RAM at any point, and still
> > > > > has reasonable battery life.
> > > > 
> > > > Android devices don't suspend to RAM. Neither do Tizen devices AFAIK.
> > > 
> > > Actually, Android devices have historically always suspended the CPU
> > > whenever there wasn't a wakelock keeping the device to suspend.  You
> > > might not consider this "suspend to RAM" but in fact it uses the
> > > identical kernel and hardware facilities as the legacy "suspend to
> > > RAM" mechanism.
> > 
> > I wouldn't consider this "suspend to RAM", but that's because I expect
> > the firmware to implement most of that. Anyway, that's splitting
> > hair.
> 
> Could you rephrase that?
> 
> Anyway, this is "echo mem > /sys/power/state" or
> suspend-to-RAM. Android does the same, with more tricky wakeup logic. 
> 
> > > > I don't think anyone was discussing cell phones in particular in this
> > > > thread, and knowing when user-space got woken up because of the baseband
> > > > processor having information for us would still be useful.
> > > 
> > > It matters because for laptops, what's important is whether the lid is
> > > closed or not.  Whether and how the laptop was "woken" is really
> > > beside the point, as others have argued.  Your counter argument is
> > > that tablets don't have lids.  But tablets are going to be using
> > > schemes similar to Android, Tizen, and Maemo, and they are *not* going
> > > to be using the legacy suspend-to-RAM model, because it's not
> > > sufficiently good at power saving.
> > 
> > There are plenty of tablets around that aren't Android devices. There
> > are plenty of laptops that can be switched to a tablet mode for which
> > this wouldn't apply either.
> 
> Yes, still the right question is "was the power button pressed while
> userland was suspended" not "was the system woken by power
> button"...

"Was the power button pressed while userland was suspended" is
presumably also racy.

>  and yes, I guess kernel should add the "power button" event
> to the input queue, even if that press was used to wake up the system.

And how would one know whether to suspend or resume in this case?

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