docs: hwmon: add max31760 documentation

Adding documentation for max31760 fan speed controller

Signed-off-by: Ibrahim Tilki <Ibrahim.Tilki@analog.com>
Link: https://lore.kernel.org/r/20220910171945.48088-3-Ibrahim.Tilki@analog.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Documentation/hwmon/index.rst

@@ -133,6 +133,7 @@ Hardware Monitoring Kernel Drivers
    max20751
    max31722
    max31730
+   max31760
    max31785
    max31790
    max34440

Documentation/hwmon/max31760.rst

@@ -0,0 +1,77 @@
+.. SPDX-License-Identifier: GPL-2.0-or-later
+
+Kernel driver max31760
+======================
+
+Supported chips:
+  * Analog Devices MAX31760
+
+    Prefix: 'max31760'
+
+    Addresses scanned: none
+
+    Datasheet: https://datasheets.maximintegrated.com/en/ds/MAX31760.pdf
+
+
+Author: Ibrahim Tilki <Ibrahim.Tilki@analog.com>
+
+Description
+-----------
+
+The MAX31760 integrates temperature sensing along with precision PWM fan
+control. It accurately measures its local die temperature and the remote
+temperature of a discrete diode-connected transistor, such as a 2N3906,
+or a thermal diode commonly found on CPUs, graphics processor units (GPUs),
+and other ASICs. Multiple temperature thresholds, such as local
+high/overtemperature (OT) and remote high/overtemperature, can be set by an
+I2C-compatible interface. Fan speed is controlled based on the temperature
+reading as an index to a 48-byte lookup table (LUT) containing
+user-programmed PWM values. The flexible LUT-based architecture enables
+the user to program a smooth nonlinear fan speed vs. temperature transfer
+function to minimize acoustic fan noise. Two tachometer inputs allow
+measuring the speeds of two fans independently. When the local or remote
+OT threshold is exceeded, the SHDN pin is asserted low and can be used to
+shut down the system. A dedicated ALERT pin reports that either a local or
+remote high-temperature threshold has been exceeded.
+
+Temperature measurement range: from -55°C to 125°C
+
+Temperature Resolution: 11 Bits, ±0.125°C
+
+Please refer how to instantiate this driver: Documentation/i2c/instantiating-devices.rst
+
+Lookup table for auto fan control
+---------------------------------
+
+========= =================================
+LUT Index Name
+========= =================================
+1         PWM value for T < +18°C
+2         PWM value for +18°C ≤ T < +20°C
+3         PWM value for +20°C ≤ T < +22°C
+...       ...
+47        PWM value for +108°C ≤ T < +110°C
+48        PWM value for T ≥ +110°C
+========= =================================
+
+Sysfs entries
+-------------
+
+=============================== =================================================================================
+fan[1-2]_input                  Fan speed (in RPM)
+fan[1-2]_enable                 Enable fan readings and fan fault alarms
+fan[1-2]_fault                  Fan fault status
+temp[1-2]_label                 "Remote" and "Local" temperature channel labels
+temp[1-2]_input                 Temperature sensor readings (in millidegrees Celsius)
+temp1_fault                     Remote temperature sensor fault status
+temp[1-2]_max                   Temperature max value. Asserts "ALERT" pin when exceeded
+temp[1-2]_max_alarm             Temperature max alarm status
+temp[1-2]_crit                  Temperature critical value. Asserts "SHDN" pin when exceeded
+temp[1-2]_crit_alarm            Temperature critical alarm status
+pwm1                            PWM value for direct fan control
+pwm1_enable                     1: direct fan control, 2: temperature based auto fan control
+pwm1_freq                       PWM frequency in hertz
+pwm1_auto_channels_temp         Temperature source for auto fan control. 1: temp1, 2: temp2, 3: max(temp1, temp2)
+pwm1_auto_point[1-48]_pwm       PWM value for LUT point
+pwm1_auto_point_temp_hyst       Temperature hysteresis for auto fan control. Can be either 2000mC or 4000mC
+=============================== =================================================================================