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Subject: Re: [PATCH v2 resend 2/2] iio: documentation: Document accelerometer
 label use
To:     Bastien Nocera <hadess@hadess.net>,
        Marcel Holtmann <marcel@holtmann.org>,
        Johan Hedberg <johan.hedberg@gmail.com>,
        Luiz Augusto von Dentz <luiz.dentz@gmail.com>
Cc:     linux-bluetooth@vger.kernel.org,
        Dmitry Torokhov <dmitry.torokhov@gmail.com>,
        Mark Pearson <mpearson@lenovo.com>
References: <20210405203933.17282-1-hdegoede@redhat.com>
 <20210405203933.17282-3-hdegoede@redhat.com>
 <dcd78309d7bbbdad511e10a63eb0e73f01934e8b.camel@hadess.net>
From:   Hans de Goede <hdegoede@redhat.com>
Message-ID: <871895f8-b85e-e8b0-83f1-de91636ce572@redhat.com>
Date:   Fri, 16 Apr 2021 13:05:38 +0200
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Hi,

On 4/16/21 12:56 PM, Bastien Nocera wrote:
> On Mon, 2021-04-05 at 22:39 +0200, Hans de Goede wrote:
>> Some 2-in-1 laptops / convertibles with 360° (yoga-style) hinges,
>> have 2 accelerometers, 1 in their base and 1 in their display.
>>
>> In many cases the kernel can detect the location of each
>> accelerometer
>> based on e.g. information from the ACPI tables.
>>
>> It is important for userspace to know the location of the 2
>> accelerometers.
>> Rather then adding a new sysfs-attribute for this we can relay this
>> information to userspace by using standardized label strings for
>> this.
>> This mirrors how this is done for proximity sensors.
>>
>> This commit documents 2 new standardized label strings for this
>> purpose:
>> "accel-base"
>> "accel-display"
> 
> If we have a combined proximity and accelerometer sensor (which
> wouldn't be unheard off with sensor hubs being used), how are multiple
> labels, say "proximity-wifi" and "accel-base" documented?

Sensor hubs typically use one iio device per sensor, see e.g.
how HID-sensors work. And if a device which does not use separate
iio-devices per sensor shows up then the plan is to use per
channel-labels which are already supported by iio.

Regards,

Hans


>> Note the "base" and "display" suffixes were chosen to match the
>> values
>> used for the systemd/udev hwdb.d/60-sensor.hwdb file's ACCEL_LOCATION
>> property.
>>
>> Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
>> Cc: Mark Pearson <mpearson@lenovo.com>
>> Cc: Bastien Nocera <hadess@hadess.net>
>> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
>> ---
>>  Documentation/ABI/testing/sysfs-bus-iio | 7 +++++++
>>  1 file changed, 7 insertions(+)
>>
>> diff --git a/Documentation/ABI/testing/sysfs-bus-iio
>> b/Documentation/ABI/testing/sysfs-bus-iio
>> index 7379e40d862d..b7529bca83f5 100644
>> --- a/Documentation/ABI/testing/sysfs-bus-iio
>> +++ b/Documentation/ABI/testing/sysfs-bus-iio
>> @@ -72,6 +72,13 @@ Description:
>>                 calculated by firmware from other sensor readings,
>> rather then
>>                 being a raw sensor reading.
>>  
>> +               For accelerometers used in 2-in-1s with 360° (yoga-
>> style) hinges,
>> +               which have an accelerometer in both their base and
>> their display,
>> +               the following standardized labels are used:
>> +
>> +               * "accel-base"
>> +               * "accel-display"
>> +
>>  What:          /sys/bus/iio/devices/iio:deviceX/current_timestamp_cl
>> ock
>>  KernelVersion: 4.5
>>  Contact:       linux-iio@vger.kernel.org
> 
>