[RFC PATCH] iio: Add some kerneldoc for channel types

From: Matti Vaittinen
Date: Fri Feb 24 2023 - 08:02:55 EST

For occasional contributor like me navigating the IIO channel types and
modifiers may be a daunting task. One may have hard time finding out
what type of channel should be used for device data and what units the
data should be converted.

There is a great documentation for the sysfs interfaces though. What is
missing is mapping of the channel types and modifiers to the sysfs
documentation (and entries in documentation).

Give a hand to a driver writer by providing some documentation and by
pointing to the sysfs document from the kerneldocs of respective enums.

Signed-off-by: Matti Vaittinen <mazziesaccount@xxxxxxxxx>
---
Please note that this RFC patch should not be applied as is. The docs
have TODO comments regarding units for IIO_ELECTRICALCONDUCTIVITY,
IIO_PHASE and IIO_RESISTANCE. I'll fix these TODOs, remove RFC and respin
if anyone familiar with the values provided via sysfs could provide me the
corret units for these channels. I am also open to any suggestions how
to better link from enum documentation to specific entry at the IIO sysfs
documetation.

Initial discussion about these docs can be found from:
https://lore.kernel.org/all/0e0d45b7-e582-82b2-9bac-1f70f9dad9f7@xxxxxxxxx/
---
include/uapi/linux/iio/types.h | 140 ++++++++++++++++++++++++++++++++-
1 file changed, 139 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/iio/types.h b/include/uapi/linux/iio/types.h
index c79f2f046a0b..e6329d3cc055 100644
--- a/include/uapi/linux/iio/types.h
+++ b/include/uapi/linux/iio/types.h
@@ -10,7 +10,129 @@

#ifndef _UAPI_IIO_TYPES_H_
#define _UAPI_IIO_TYPES_H_
-
+/**
+ * iio_chan_type - Type of data transferred via IIO channel.
+ *
+ * The 'main' type of data transferred via channel. Please note that most
+ * devices need to specify also a more accurate 'sub category'. See the
+ * enum iio_modifier for this. (For example, IIO_ACCEL channel often needs to
+ * specify the direction. IIO_CONCENTRATION specifies the type of substance
+ * it measures etc).
+ *
+ * Use of correct units is required but scale and offset that user must apply
+ * to channel values can be advertised.
+ *
+ * Please find the detailed documentation for reported values from the
+ * Documentation/ABI/testing/sysfs-bus-iio.
+ *
+ * IIO_ACCEL: Acceleration, m/s^2
+ * Doc keyword: in_accel_x_raw
+ *
+ * IIO_ACTIVITY: Activity state. For example a pedometer signaling
+ * jogging, walking or staying still.
+ * Doc keyword: in_activity_still_thresh_rising_en
+ *
+ * IIO_ALTVOLTAGE:
+ *
+ * IIO_ANGL: Angle of rotation, radians.
+ * Doc keyword: in_angl_raw
+ *
+ * IIO_ANGL_VEL: Angular velocity, rad/s
+ * Doc keyword: in_anglvel_x_raw
+ *
+ * IIO_CAPACITANCE: Capacitance, nanofarads.
+ * Doc keyword: in_capacitanceY_raw
+ *
+ * IIO_CCT:
+ *
+ * IIO_CURRENT: Current, milliamps
+ * Doc keyword: in_currentY_raw
+ *
+ * IIO_CONCENTRATION: Reading of a substance, percents. Used for example by
+ * deviced measuring amount of CO2, O2, ethanol...
+ * Doc keyword: in_concentration_raw
+ *
+ * IIO_COUNT: Deprecated, please use counter subsystem.
+ *
+ * IIO_DISTANCE: Distance in meters. Typically used to report measured
+ * distance to an object or the distance covered by the
+ * user
+ * Doc keyword: in_distance_input
+ *
+ * IIO_ELECTRICALCONDUCTIVITY: electric conductivity, siemens per meter
+ * Doc keyword: in_electricalconductivity_raw
+ * TODO: What does "can be processed to siemens per meter"
+ * mean? Do we have unit requirement?
+ *
+ * IIO_ENERGY: Energy in Joules. Typically reported by a device
+ * measuring energy burnt by the user.
+ * Doc keyword: in_energy_input
+ *
+ * IIO_GRAVITY: Gravity, m/s^2
+ * Doc keyword: in_gravity_x_raw
+ *
+ * IIO_HUMIDITYRELATIVE: Relative humidity, percents
+ * Doc keyword: in_humidityrelative_raw
+ *
+ * IIO_INCLI: Inclination, degrees
+ * Doc keyword: in_incli_x_raw
+ *
+ * IIO_INDEX: Deprecated, please use Counter subsystem
+ *
+ * IIO_INTENSITY: Unitless intensity.
+ * Doc keyword: in_intensityY_raw
+ *
+ * IIO_LIGHT: Visible light intensity, lux
+ * Doc keyword: in_illuminance_raw
+ *
+ * IIO_MAGN: Magnetic field, Gauss.
+ * Doc keyword: in_magn_x_raw
+ *
+ * IIO_MASSCONCENTRATION: Mass concentration, ug / m3
+ * Doc keyword: in_massconcentration_pm1_input
+ *
+ * IIO_PH: pH reading, negative base-10 logarithm of hydrodium
+ * ions in a litre of water
+ * Doc keyword: in_ph_raw
+ *
+ * IIO_PHASE: Phase difference, radians
+ * Doc keyword: in_phaseY_raw
+ * TODO: What does "can be processed to radians" mean? Do
+ * we have unit requirement?
+ *
+ * IIO_POSITIONRELATIVE: Relative position.
+ * Doc keyword: in_positionrelative_x_raw
+ *
+ * IIO_POWER: Power, milliwatts
+ * Doc keyword: in_powerY_raw
+ *
+ * IIO_PRESSURE: Pressure, kilopascal
+ * Doc keyword: in_pressureY_raw
+ *
+ * IIO_RESISTANCE: Resistance, ohms
+ * Doc keyword: in_resistance_raw
+ * TODO: What means "can be processed..." Do we have unit
+ * requirement?
+ *
+ * IIO_ROT: Euler angles, deg
+ * Doc keyword: in_rot_yaw_raw
+ *
+ * IIO_STEPS: Steps taken by the user
+ * Doc keyword: in_steps_input
+ *
+ * IIO_TEMP: Temperature, milli degrees Celsius
+ * Doc keyword: in_temp_raw
+ *
+ * IIO_UVINDEX: UV light intensity index
+ * Doc keyword: in_uvindex_input
+ *
+ * IIO_VELOCITY: Current speed (norm or magnitude of the velocity
+ * vector), m/s
+ * Doc keyword: in_velocity_sqrt(x^2+y^2+z^2)_input
+ *
+ * IIO_VOLTAGE: Voltage, millivolts
+ * Doc keyword: in_voltageY_raw
+ */
enum iio_chan_type {
IIO_VOLTAGE,
IIO_CURRENT,
@@ -49,6 +171,22 @@ enum iio_chan_type {
IIO_MASSCONCENTRATION,
};

+/**
+ * iio_modifier - accurate class for channel data
+ *
+ * IIO_MOD_<X,Y,Z>: Value represents <X,Y,Z>-axis data.
+ * Typically used by channels of type:
+ * IIO_ACCEL, IIO_TEMP, IIO_GRAVITY, IIO_POSITIONRELATIVE,
+ * IIO_ANGL_VEL, IIO_INCLI, IIO_MAGN
+ * IIO_MOD_LIGHT_BOTH: Value contains visible and infra red light components
+ * IIO_MOD_LIGHT_IR: Value represents infra-red radiation
+ * IIO_MOD_LIGHT_<RED, GREEN, BLUE>:
+ * Value represents visible <red, green, blue> light
+ * IIO_MOD_LIGHT_CLEAR: Value represents all visible light frequencies
+ *
+ * Please find the detailed documentation for reported values from the
+ * Documentation/ABI/testing/sysfs-bus-iio.
+ */
enum iio_modifier {
IIO_NO_MOD,
IIO_MOD_X,

base-commit: c9c3395d5e3dcc6daee66c6908354d47bf98cb0c
--
2.39.2


--
Matti Vaittinen, Linux device drivers
ROHM Semiconductors, Finland SWDC
Kiviharjunlenkki 1E
90220 OULU
FINLAND

~~~ "I don't think so," said Rene Descartes. Just then he vanished ~~~
Simon says - in Latin please.
~~~ "non cogito me" dixit Rene Descarte, deinde evanescavit ~~~
Thanks to Simon Glass for the translation =]

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