Re: [External] Using IIO to export laptop palm-sensor and lap-mode info to userspace?

[Dmitry Torokhov <dmitry.torokhov@gmail.com>]

On Wed, Oct 07, 2020 at 11:51:05AM +0200, Hans de Goede wrote:
> Hi,
> 
> On 10/7/20 10:36 AM, Jonathan Cameron wrote:
> > On Mon, 5 Oct 2020 22:04:27 -0400
> > Mark Pearson <markpearson@lenovo.com> wrote:
> > 
> > > Adding Nitin, lead for this feature, to the thread
> > 
> > +CC linux-input and Dmitry for reasons that will become clear below.
> > > 
> > > On 2020-10-03 10:02 a.m., Hans de Goede wrote:
> > > > Hi All,
> > > > 
> > > > Modern laptops can have various sensors which are kinda
> > > > like proximity sensors, but not really (they are more
> > > > specific in which part of the laptop the user is
> > > > proximate to).
> > > > 
> > > > Specifically modern Thinkpad's have 2 readings which we
> > > > want to export to userspace, and I'm wondering if we
> > > > could use the IIO framework for this since these readings
> > > > are in essence sensor readings:
> > > > 
> > > > 1. These laptops have a sensor in the palm-rests to
> > > > check if a user is physically proximate to the device's
> > > > palm-rests. This info will be used by userspace for WWAN
> > > > functionality to control the transmission level safely.
> > > > 
> > > > A patch adding a thinkpad_acpi specific sysfs API for this
> > > > is currently pending:
> > > > https://patchwork.kernel.org/patch/11722127/
> > > > 
> > > > But I'm wondering if it would not be better to use
> > > > IIO to export this info.
> > 
> > My first thought on this is it sounds more like a key than a sensor
> > (simple proximity sensors fall into this category as well.)

[ sorry for sitting on this thread for so long ]

So I think the important question here is if we only ever want yes/no
answer, or if we can consider adjusting behavior of the system based on
the "closeness" of an object to the device, in which case I think IIO is
more flexible.

FWIW in Chrome OS land we name IIO proximity sensors using a scheme
"proximity-lte", "proximity-wifi", "proximity-wifi-left",
"proximity-wifi-right", etc, and then userspace implements various
policies (SAR, etc) based off it.

> 
> That is an interesting suggestion. Using the input/evdev API
> would have some advantages such as being able to have a single
> event node for all the proximity switches and then being able
> to pass a fd to that from a privileged process to a non
> privileged one, something which userspace already has
> various infrastructure for.

I am not sure if multiplexing all proximity switches into one evdev node
is that great option, as I am sure we'll soon have devices with 2x
palmrest switches and being capable finely adjusting transmit power,
etc.

Thanks.

-- 
Dmitry