Re: A desktop environment[1] kernel wishlist

[Bastien Nocera <hadess@hadess.net>]

On Thu, 2014-10-30 at 19:23 +0100, Pavel Machek wrote:
> On Thu 2014-10-30 16:07:35, Bastien Nocera wrote:
> > On Thu, 2014-10-30 at 07:53 -0700, Andy Lutomirski wrote:
> > > On Thu, Oct 30, 2014 at 7:45 AM, Bastien Nocera <hadess@hadess.net> wrote:
> > > > On Wed, 2014-10-29 at 22:16 +0100, Pavel Machek wrote:
> > > >> On Wed 2014-10-29 16:26:16, Theodore Ts'o wrote:
> > > >> > On Wed, Oct 29, 2014 at 12:19:56PM -0700, Andy Lutomirski wrote:
> > > >> > > For a tablet, isn't the relevant piece of information whether the power
> > > >> > > button was recently pressed, not whether the power button caused the wakeup?
> > > >> >
> > > >> > For Android L devices, it has been reported that the device might
> > > >> > power up its screen fully (note I didn't say 'wake up') automatically
> > > >> > when it detects that you are picking it up, or when you double-tap the
> > > >> > screen.  It also reportedly has a low power black and white "ambient
> > > >> > display" (ala the Android Wear devics) which allows you to see
> > > >> > notifications without waking up the phone all the way[1].  (All of
> > > >> > this assuming appropriate hardware support, of course.)
> > > >> >
> > > >> > [1] http://www.androidauthority.com/ambient-display-lollipop-541198/
> > > >> >
> > > >> > Which goes back to the concept of having a "suspend" mode is legacy
> > > >> > thinking.  Modern devices will soon have not just a "awake" and a
> > > >> > "asleep" modes; there will be (well, is now) a much wider spectrum of
> > > >> > modes, with the goal of using the minimum amount of power while still
> > > >> > providing use functionality to the user.
> > > >>
> > > >> 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.
> > > >
> > > >> So I agree -- using suspend to RAM on "active" cell phone is just a
> > > >> bad design.
> > > >
> > > > 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.
> > > >
> > > 
> > > You still haven't addressed what problem this solves that isn't solved
> > > by merely knowing whether the baseband processor has useful
> > > information.
> > 
> > We don't know that the baseband processor has useful information if
> > we're not in the "path" for the interrupt that it would send. This event
> > might end up dying somewhere inside the kernel for all we know.
> 
> See, that would be something to fix. If baseband has incoming data,
> and kernel fails to notify userspace about that data after resume,
> that is a kernel bug.

It might notify through a specific socket, through a specific service,
but the outside observer, one that's not directly in the path to that
event, will be unaware. Coalescing all the information taking different
routes from the harwdare to user-space can be very difficult, and it's
already difficult to observe the reason for wakeup without being part of
that event's path.

Having drivers export that information would allow us to know why
something was woken up.