Re: [linux-pm] [RFC] input: syfs switches for SKE keypad

["Rafael J. Wysocki" <rjw@sisk.pl>]

On Wednesday, October 06, 2010, Dmitry Torokhov wrote:
> On Wed, Oct 06, 2010 at 02:19:03PM -0400, Alan Stern wrote:
> > On Wed, 6 Oct 2010, Dmitry Torokhov wrote:
> > 
> > > > > I think last time Rafael mentioned that runtime PM did not allow for
> > > > > forcing power state from userspace but I wonder if it would be possible
> > > > > for userspace to signal and "accelerate" the idle state for a device and
> > > > > then standard runtime PM framework would kick in...
> > > > 
> > > > Yes; drivers can implement their runtime power policy any way they
> > > > want.  For example, a driver could create a sysfs attribute file which
> > > > userspace could use to ask for changes in the power state.
> > > > 
> > > > The real question is whether the driver is platform-specific.  If it is
> > > > then fine, it can do whatever it wants.  If it isn't then it should
> > > > try to avoid doing things that are tied to a specific platform.
> > > >
> > > 
> > > No, I really think it is wrong. This what leads us to the situation we
> > > are in at the moment. Every device [re]implements  its own little knobs
> > > to do power management. Accelerometers export their (often tailored to a
> > > specific platform) attributes in sysfs in nonstandard way. And so on,
> > > and so forth.
> > > 
> > > Here I'd like to see these (PM) hooks done on device core level, i.e.
> > > the knobs should be unified and live in /sys/devices/.../deviceX/power/
> > 
> > I haven't followed this thread in detail.  What sort of knobs are you 
> > talking about?  That is, what needs to be done?  Maybe the PM core 
> > already provides these features.
> > 
> 
> Mobile folks wish to power down some devices (most often input -
> touchscreen, keypad) under certain circumstances to save power.
> So far they were doing that by adding "disable" hook to individual
> drivers and while I did allow that in for some devices I feel that we
> need more standardised solution, preferably one that could re-use
> existing PM hooks in drivers.

There's no interface for that at the PM core level, but I think we should
add it, perhaps in analogy to the autosuspend one.  Namely, we can add a
flag for drivers who want to make their suspend/resume callbacks to be
reachable directly from user space.  Setting that flag would enable a sysfs
attribute in /sys/devices/.../power/ allowing user space to invoke
pm_runtime_suspend() and pm_runtime_resume() for the given device.

Thanks,
Rafael