linux-kernel - Re: [RFC PATCH 01/06] input/rmi4: Public header and documentation

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Date:	Thu, 11 Oct 2012 17:22:45 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Christopher Heiny <Cheiny@...aptics.com>,
	Anton Vorontsov <anton.vorontsov@...aro.org>
Cc:	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Jean Delvare <khali@...ux-fr.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Linux Input <linux-input@...r.kernel.org>,
	Allie Xiong <axiong@...aptics.com>,
	Vivian Ly <vly@...aptics.com>,
	Daniel Rosenberg <daniel.rosenberg@...aptics.com>,
	Joerie de Gram <j.de.gram@...il.com>,
	Wolfram Sang <w.sang@...gutronix.de>,
	Mathieu Poirier <mathieu.poirier@...aro.org>,
	Linus Walleij <linus.walleij@...ricsson.com>,
	Naveen Kumar Gaddipati <naveen.gaddipati@...ricsson.com>,
	Alexandra Chin <alexandra.chin@...synaptics.com>
Subject: Re: [RFC PATCH 01/06] input/rmi4: Public header and documentation

On Thu, Oct 11, 2012 at 5:41 AM, Christopher Heiny <Cheiny@...aptics.com> wrote:
> Linus Walleij wrote:
>> On Sat, Oct 6, 2012 at 6:09 AM, Christopher Heiny <cheiny@...aptics.com> wrote:

>> > +          chargerinput ... (rw) User space programs can use this to tell
>> > the +                  sensor that the system is plugged into an external
>> > power +                  source (as opposed to running on
>> > batteries).  This allows +                  the sensor firmware to make
>> > necessary adjustments for the +                  current capacitence
>> > regime.  Write 1 to this when the +                  system is using
>> > external power, write 0 to this when the +                  system is
>> > running on batteries.  See spec for full details.
>> I remember discussing in-kernel notifiers for this. I don't
>> really see the point in tunnelling a notification from the drivers/power
>> subsystem to the drivers/input subsystem through userspace for
>> no good.
>>
>> It's no blocker though, I don't expect you to fix this as part of
>> this driver submission.
>>
>> Maybe Anton can comment?
>
> Hmmm.  I agree that it'd be good to avoid looping through userspace.  But....
>
> I found ways to notfiy the kernel that the charger is plugged/unplugged,
> but that's only useful if you're a battery charger device driver.  I also
> found ways for userspace to get notification of charger events.  I
> didn't spot any way for in-kernel drivers to get notification of such
> events.  Perhaps I'm not looking the right places, though - can you
> provide a pointer?

So my point was that there is indeed no such in-kernel
notification mechanism.

Maybe something engineered similar to this:
http://www.spinics.net/lists/lm-sensors/msg33834.html

Yours,
Linus Walleij
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