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

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Message-ID: <20141028225740.2cd0ea5f@alan.etchedpixels.co.uk>
Date:	Tue, 28 Oct 2014 22:57:40 +0000
From:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
To:	John Stultz <john.stultz@...aro.org>
Cc:	Bastien Nocera <hadess@...ess.net>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: A desktop environment[1] kernel wishlist

> If the firmware eats that button (which I hope it wouldn't, but I
> probably should know better then to expect sane behavior), how does
> the kernel know anything more?

The firmware is generally going to do whatever it believes is "correct",
which may nor may not be determined by what the hardware itself does
(if wakeup is a GPIO off the controller then it'll be determined by the
widget the other end what is eaten)
 
> button). If those button presses don't reliably get communicated, I
> think that's a better problem to solve in the kernel.

You'd have to solve it in the firmware.

> But the other part of why I'm pushing back is that on future hardware,
> we may not have a "suspend" mode, and systems may just be in a deep
> idle, with selected interrupts disabled 

Nothing future about this. Some ARM devices have had that kind of mindset
for a long time, some x86 platforms can run that way but don't currently
do so under Linux (eg Baytrail/T). On those x86 platforms 'suspend' and
'resume' are in fact entirely Linux constructs to fake legacy behaviour
on top of an ultra low power idle.

If you are planning for the future then I wouldn't be too hooked on ideas
like "suspend", "lid switches" or assumptions that a "closed" device
should be kept suspended. It's a broken model. It's bad enough that
systemd tries to do magic hackery to fake this up and gets it wrong in
some case (despite making a very good effort) without propogating the mess
further.

- S3 has already gone away on some Intel SoC devices
- Suspend/Resume on such machines are a Linux fake to keep legacy code
  happy
- In such an environment your "wakeup" model changes entirely because you
  drop into deep idle whever there isn't stuff annoying the CPU
  regularly. With the right kinds of video and audio that could even mean
  doing it between keypresses (feature parity approaching 1980s 8bit
  laptops ;-) )

Instead think long term that

- There may be no such thing as suspend or resume, just make your code
  very well behaved on wakeup events, and closing unneeded
  devices/resources whenever it can.
- On/off is an extreme action rarely taken (feature parity with 1970s
  VAXen ;-) )
- The "blob with a lid" model of construction is no longer useful. Even a
  keyboarded device is quite likely have a removable keyboard.

Alan
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