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

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Thu, 19 Nov 2020 16:39:07 +0100
Hans de Goede <hdegoede@redhat.com> wrote:

> Hi,
> 
> On 11/13/20 7:58 AM, Dmitry Torokhov wrote:
> > On Thu, Nov 12, 2020 at 10:50:12AM +0100, Hans de Goede wrote:  
> >> 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 ?  
> > 
> > I think it depends on the kernel we use and architecture. On x86 I think
> > we rely on udev, like this:
> > 
> > https://chromium.googlesource.com/chromiumos/overlays/board-overlays/+/master/overlay-nocturne/chromeos-base/chromeos-bsp-nocturne/files/udev/99-cros-sx-proximity.rules
> > 
> > DEVPATH=="*/pci0000:00/0000:00:15.1/*", SYMLINK+="proximity-wifi-right"
> > DEVPATH=="*/pci0000:00/0000:00:19.1/*", SYMLINK+="proximity-wifi-left"
> > ATTR{events/in_proximity1_USE_CS1_thresh_either_en}="1"  
> 
> So that results in a symlink under /dev, right ? That seems like
> it is not really compatible with how most modern userspace discovers
> hw (through udev). Although I guess code using udev could still
> lookup the symlink in the udev per device data, this just not feel
> like a good way forward.
> 
> > On newer ARM we use "label" attribute in DTS:
> > 
> > arch/arm64/boot/dts/qcom/sc7180-trogdor.dtsi
> > 
> >         ap_sar_sensor: proximity@28 {
> >                 compatible = "semtech,sx9310";
> >                 reg = <0x28>;
> >                 #io-channel-cells = <1>;
> >                 pinctrl-names = "default";
> >                 pinctrl-0 = <&p_sensor_int_l>;
> > 
> >                 interrupt-parent = <&tlmm>;
> >                 interrupts = <24 IRQ_TYPE_LEVEL_LOW>;
> > 
> >                 vdd-supply = <&pp3300_a>;
> >                 svdd-supply = <&pp1800_prox>;
> > 
> >                 status = "disabled";
> >                 label = "proximity-wifi";
> >         };  
> 
> Hmm, interesting. I did not know iio-devices could
> have a label sysfs attribute (nor that that could be
> set through device-tree). I was thinking about adding
> an in_proximity_location sysfs attribute. But using
> labels (and standardizing a set of label names) will
> work nicely too.

It's fairly new.   Note we also have per channel labels
though they are 'very new'.  Might be handy if the sensors
appear as a single device despite being spread over the
laptop.

> 
> I have no real preference for this either way, so
> I guess we might as well go with labels to avoid
> having any unnecessary discrepancies between ChromeOS
> and whatever we do for the Thinkpad sensors.
> 
> Is there a know set of labels which ChromeOS is currently
> using? If we are going to use labels for this it would
> be good IMHO to define a set of standard labels for
> this in say Documentation/ABI/testing/sysfs-bus-iio-labels.

If you do want to do this, please just put it under sysfs-bus-iio
doc.  I want this to be in the top level doc and there is an issue
we are currently trying to sort out with autogenerated docs and
repeats of a given filename in the ABI docs.
(basically it doesn't work and generates lots of warnings!)

Thanks,

Jonathan

> 
> >> 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).  
> > 
> > One of the sensors we use is sx9310 that I believe can report range, but
> > I think we configure them to trigger when a threshold is crossed.
> > 
> > Events are handled by our powerd:
> > 
> > https://chromium.googlesource.com/chromiumos/platform2/+/master/power_manager/powerd/system/sar_watcher.cc
> >   
> >>
> >> Perhaps you can provide an URL to the kernel code implementing these ?  
> > 
> > drivers/iio/proximity/sx9310.c  
> 
> If I'm reading that correctly the it exports a raw "distance"
> reading and a suggested threshold value for the code interpreting
> the reading to use.
> 
> So that would be a bit different then the Thinkpad sensors, but
> exporting just a 0-1 range for the in_proximity_raw value for the
> Thinkpad case should not be a problem. Or we could just make it
> repot 0 and 100 and export a fixed in_proximity_nearlevel of 50,
> that would make the userspace API more like other proximity sensors.
> 
> Regards,
> 
> Hans
> 
> 
> 
>