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

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

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"

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";
        };

> 
> 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

Also sx932x - https://lore.kernel.org/patchwork/patch/1005708/

Thanks.

-- 
Dmitry