linux-kernel - Re: [PATCH 3/5] toshiba_acpi: Add accelerometer input polled device

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Date:	Tue, 9 Sep 2014 20:35:20 -0700
From:	Darren Hart <dvhart@...radead.org>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Azael Avalos <coproscefalo@...il.com>,
	Jonathan Cameron <jic23@...nel.org>,
	Matthew Garrett <matthew.garrett@...ula.com>,
	"platform-driver-x86@...r.kernel.org" 
	<platform-driver-x86@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-iio@...r.kernel.org
Subject: Re: [PATCH 3/5] toshiba_acpi: Add accelerometer input polled device

On Mon, Sep 08, 2014 at 06:35:53PM -0700, Greg Kroah-Hartman wrote:
> On Mon, Sep 08, 2014 at 05:04:30PM -0700, Darren Hart wrote:
> > On Fri, Sep 05, 2014 at 11:04:18PM -0600, Azael Avalos wrote:
> > > Hi there,
> > > 
> > > 2014-09-05 20:42 GMT-06:00 Darren Hart <dvhart@...radead.org>:
> > > > On Fri, Sep 05, 2014 at 11:14:05AM -0600, Azael Avalos wrote:
> > > >> The accelerometer sensor is very sensitive, and having userspace
> > > >> poll the sysfs position entry is not very battery friendly.
> > > >>
> > > >> This patch removes the sysfs entry and instead, it creates an
> > > >> input polled device (joystick) for the built-in accelerometer.
> > > >
> > > > Hrm, while sysfs details can change across kernel versions, usually due to
> > > > driver core changes, we try to keep them as consistent as possible so as not to
> > > > break userspace.
> > > >
> > > > That said, if we are going to try and come up with a better model for
> > > > representing an accelerometer, wouldn't treating it as an IIO device be the more
> > > > logical approach?
> > > 
> > > Yes of course, but the actual accelerometer device (sensor?) is not
> > > really exposed,
> > > only certain "functions" it provides, and they are divided across two
> > > different ACPI devices,
> > > TOS620A exposes the protection, and the TOS1900 (and et. al.) only
> > > exposes the axes.
> > 
> > As I understand it, IIO defines an interface to a device, a standard sysfs set
> > of properties. I should think we could provide the appropriate callbacks even
> > for a partially implemented (or a pair of) accelerometer.
> > 
> > Jonathan, what are your thoughts here. Is such a "device" (ACPI accessors to
> > axis and threshold) a candidate for IIO, or is this input polled device more
> > appropriate?
> > 
> > > 
> > > I see your point in breaking userspace, but given the fact that it was
> > > recently introduced,
> > > I didn't thought it was already "adopted", that's why I decided to
> > > remove the sysfs entry.
> > 
> > Looks like since 3.15 if I read the log correctly. That is fairly recent and
> > this is not one of the "defined interfaces" in the sysfs documentation.
> > 
> > Greg, can you weigh in here - does this change count as "breaking userspace", or
> > is this more inline with the scheduler knobs in /proc/sched_debug which can
> > change from version to version.
> > 
> > > 
> > > Then we might as well keep the sysfs entry and have the input polled
> > > device as well.
> > 
> > Let's see what Greg has to say. If he isn't bothered by the change, I won't push
> > the issue.
> 
> If it should be an IIO device, great, make it an IIO device, and move
> away from a custom sysfs interface that matches nothing else.
> 
> But I really doubt it should be a joystick device, that just doesn't
> make sense at all.

I immediately went to a tablet with a marble maze game and it didn't seem too
crazy, but I don't suppose that is what people are actually doing with it...

What are people actually doing with this thing Azael?

-- 
Darren Hart
Intel Open Source Technology Center
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