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

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Message-ID: <20140917183809.GA7517@vmdeb7>
Date:	Wed, 17 Sep 2014 11:38:09 -0700
From:	Darren Hart <dvhart@...radead.org>
To:	Jonathan Cameron <jic23@...nel.org>
Cc:	Azael Avalos <coproscefalo@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.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 Wed, Sep 17, 2014 at 05:36:31PM +0100, Jonathan Cameron wrote:
> 
> 
> On September 9, 2014 1:04:30 AM GMT+01:00, Darren Hart <dvhart@...radead.org> 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?
> Absolutely fine in IIO.
> 
> Sorry I took so long to reply. Read the title and expected more detailed issue so queued
>  it up for when I had more time. Oops.
> 
> Only slight gotcha is that there is some debate over the iio timer trigger
>  configuration interface which would be equivalent of a polled input device.
> 
> Hence it hasn't merged yet.
> Comes down to how these are instantiated. Lars-Peter Clausen is planning a configfs
>  proposal rather than how we do the user space trigger creation currently.
> 
> A user space trigger would work but then you loose lack of hitting sysfs files.

Thanks Jonathan,

Azael, please follow-up with the IIO folks and if you want to modify the
interface, please do so via IIO so it uses a consistent interface and we can
eliminate these custom sysfs files.

Thanks,

-- 
Darren Hart
Intel Open Source Technology Center
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