On Friday, July 18, 2014 04:16:50 PM Dmitry Torokhov wrote:

On Saturday, July 19, 2014 12:55:09 AM Rafael J. Wysocki wrote:

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On Saturday, July 19, 2014 12:19:39 AM Rafael J. Wysocki wrote:

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On Friday, July 18, 2014 02:45:40 PM Dmitry Torokhov wrote:

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On Friday, July 18, 2014 11:59:18 PM Rafael J. Wysocki wrote:

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On Friday, July 18, 2014 02:26:21 PM Dmitry Torokhov wrote:

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On Friday, July 18, 2014 04:09:46 PM Alan Stern wrote:

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On Fri, 18 Jul 2014, Patrik Fimml wrote:

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On Fri, Jul 18, 2014 at 03:00:46PM -0400, Alan Stern wrote:

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I'm not sure what the appropriate action for a video camera is
anyway.
Should it go away completely, including its device? Should it be
there,
but certainly not be the default choice when there is an
external
camera? I'm thinking along the lines of some application's
settings
dialog here, where it might be desirable to still be able to
select
the
internal camera for future recordings.

Of course, userspace could still decide simply not to
quiesce|deactivate|inhibit the device if that was desired.

There's some question about how much of userspace needs to get
involved.  Just the daemon that manages these configuration
changes, or
other programs as well?  I guess that's not really our problem...

We need to provide means of implementing policy; the policy itself
is not
really our concern ;)

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In the end, it sounds like you're suggesting a new pair of PM
callbacks: ->deactivate() and ->reactivate(), or ->inhibit() and
->uninhibit().  Plus an optional (?) sysfs interface for invoking
the
callbacks.

We do need sysfs interface so that userspace can talk to the devices
in
question; and we also need to make sure that PM core is aware of the
new
callbacks and provides guarantees about their interactions with
system-
and
runtime-PM callbacks so that individual drivers do not have to sort
it out
on their own.

A step back, please.

I have no idea why those need to be PM callbacks.

What you need really seems to be a way to tell a driver "ignore input
from
this device from now on as it is most likely bogus".  A natural
reaction of
the driver to that might be to stop processing input from the device
and
then runtime suspend it (and prevent it from generating remote wakeup
as
that may be bogus as well), but I don't see why the PM core needs to
be
involved in that at all.

So that we do not need to handle cases like:

- I am already in idle state and request comes to inhibit, what do I do
(in

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driver) or:

I'm not sure why being "suspended" or not matters here.  The PM core
doesn't know what physical state the device is in anyway and the driver
or subsystem (or another layer such as ACPI) has to track that.

Also it seems that it should be perfectly fine to ignore input from the
device without suspending it as well as it is perfectly fine to be
suspended while you are generally not ignoring the input (just because
there is no input at the moment, for example).

Yes, it make sense to suspend the device when you know you'll ignore input
going forward, but then if the real goal is to prevent bogus input from
reaching applications, then this isn't a power management problem even.

The area where it must interact with power management is wakeup, both remote
wakeup at run time and wakeup from system suspend.  In particular, there's
the question whether or not a device ignoring its input should be regarded
as a wakeup source.

I'd say no.

Anyway, even though it is very tempting to declare inhibit a "deeper" state of 
runtime suspend maybe you are right and inhibit should really be separate from 
PM and drivers would have to sort out all the possible state permutations.

Considering input devices:

input_open(): check if device is inhibited, if so do nothing. Otherwise try 
waking up itself and parent (via pm_runtime_get_sync() on itself), this will 
power up the device. Do additional configuration if needed.

input_close(): check if device is inhibited, if not do pm_runtime_put (_sync? 
to make sure we power off properly and not leave device up and running? or 
should we power down manually not waiting for runtime PM)?

pm_runtime_put_sync() should be sufficient here I think.

inhibit(): check if device is opened, if opened do pm_runtime_put_sync().

uninhibit(): if device is opened do pm_runtime_get_sync(), let runtime PM 
bring up the device. Do additional config if needed -> very similar to 
input_open(), different condition.

runtime_suspend(): power down the device. If not inhibited enable as wakeup 
source.

User space may not want it to be a wakeup source even if not inhibited
(it may not want it to wake up from system suspend, for example, like I do
with my cordless mouse).

runtime_resume(): power up the device if device is opened and not inhibited.

system_suspend(): check if device is opened, not inhibited and not in 
runtimesuspend  already; power down.

I think you only need to know if the device has been powered down already
here regardless of the reason.

system_resume(): power up the device if it is opened and not inhibited. I 
guess it's OK to wake up device that shoudl be runtime-PM-idle since it will 
go to back sleep shortly.

Ugh.. This is complicated...

If runtime PM and system suspend shared the status, we might simplify this
somewhat.  Problem is, there are drivers that don't support runtime PM, but
support system suspend.

Rafael