Date:   Fri, 24 Feb 2023 15:02:32 +0200
From:   Matti Vaittinen <mazziesaccount@...il.com>
To:     Matti Vaittinen <mazziesaccount@...il.com>,
        Matti Vaittinen <matti.vaittinen@...rohmeurope.com>
Cc:     Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Andrea Merello <andrea.merello@....it>,
        Jagath Jog J <jagathjog1996@...il.com>,
        Matti Vaittinen <mazziesaccount@...il.com>,
        linux-kernel@...r.kernel.org
Subject: [RFC PATCH] iio: Add some kerneldoc for channel types

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@...il.com>
---
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@gmail.com/
---
 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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