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

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 11/12/20 7:23 AM, Dmitry Torokhov wrote:
> 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.

Interesting, so 2 questions:

1. So your encoding the location in the sensor's parent-device name
instead of using a new sysfs attribute for this ?

2. Do these sensors just give a boolean value atm, or do they already
report a range ?  IIRC one of the objections from the iio folks in
the Lenovo case was that booleans are not really a good fit for iio
(IIRC they also said we could still use iio for this).

Perhaps you can provide an URL to the kernel code implementing these ?

>> 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.

Right, so going with iio, together with a naming scheme like used
on ChromeOS might indeed be more future proof (and make things
easier for running ChromeOS on non ChromeOS hardware and the other
way around).

Regards,

Hans