Re: [linux-pm] [PATCH v2 1/2] Input: gpio-keys - allow platform to specify exact irq flags

[Artem Bityutskiy <dedekind1@gmail.com>]

On Tue, 2009-12-08 at 09:42 -0800, Dmitry Torokhov wrote:
> > > I also see that gpio-keys is quite different in the sence that it can
> > > shut off buttons selectively. I fact, at the moment every button can be
> > > considered a separate device... But that would be too much overhead.
> > > 
> > > They could probably split the keys into 2 groups (critical that should
> > > be always active) and not critical, that could be shut off, but I think
> > > they want teh flexibility of controlling this at runtime instead of
> > > doing it in board data.
> > 
> > I suggested including this into the "abstract input device" model, but
> > you refuse this. But I still think it is a good idea.
> > 
> > Indeed, if we look at an input device as at something abstract which has
> > many keys, why we cannot assume that separate keys can be
> > enabled/disabled? Just imagine you have a very advanced keybord :-) And
> > we simply implement an ioctl which enables/disables a specific key. The
> > generic layers just pass this ioctl down to the lower lever drivers. If
> > the specific input device or driver support it - fine, if not - it
> > returns -EINVAL or something like that.
> 
> I refuse it because it will be supported by exactly 1 driver in the
> kernel - gpio-keys. It is the only driver that allows shut half of the
> "device" (because in reality it is a group of disjoint devices). It is
> the only case when "muting" a button means that IRQ is shut off abnd
> thus CPU can continue to sleep if that button is pressed. For all other
> devices that have 1 inettrupt per device, you still have to wake up,
> because you don't know whether the button that generated event is
> "important" or not.

Fair enough.

> Now, there is a issue of waking up userspace task, additional scheduling
> and keeping CPU running longer than necessary for "uninteresting" keys.
> This can be solved by implementing a subscription model which allows
> filtering uninteresing events on a per-client basis at evdev level.

Right. And for gpio_keys, this would be dine on the driver level.

> This, if implemented properly, would work for _all_ input devices out
> there. You were not interested into looking into it (because for your
> particular and only device the otehr approach promises bigger savings)
> but I think we'll get there eventually.

Well, we can (and have to, if this approach is taken) look into this in
a sense of implementing our particular task in a way that it could be
extended with this generic stuff. We might as well implement something
generic, but may be not too comprehensive, feature-full, and well-tested
(simply because we do not need it, so cannot prove usefulness on real
applications).

> And the third topic - shutting (or putting into low power) entire device
> upon request from userspace. This again has much wider auditory than
> gpio-keys, or input devices layer for that matter. We may want to do so
> for other types of devices as well. That is why the question when to
> general PM list.

Yeah.

-- 
Best Regards,
Artem Bityutskiy (Артём Битюцкий)

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