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

[Artem Bityutskiy <dedekind1@gmail.com>]

On Wed, 2009-12-09 at 10:03 -0800, Dmitry Torokhov wrote:
> On Wed, Dec 09, 2009 at 09:31:00AM +0200, Artem Bityutskiy wrote:
> > 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.
> 
> But the semantics are different - if done on driver level you'd be
> affecting _all_  consumers of the device; what I want to be done only
> affects owner of the file descriptor.

OK, makes sense. I'm convinced, thanks!

-- 
Best Regards,
Artem Bityutskiy (Артём Битюцкий)

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