hwmon: (pmbus) Add support for MPS Multi-phase mp2975 controller

Add support for mp295 device from Monolithic Power Systems, Inc. (MPS)
vendor. This is a dual-loop, digital, multi-phase controller.
This device:
- Supports two power rail.
- Provides 8 pulse-width modulations (PWMs), and can be configured up
  to 8-phase operation for rail 1 and up to 4-phase operation for rail
  2.
- Supports two pages 0 and 1 for telemetry and also pages 2 and 3 for
  configuration.
- Can configured VOUT readout in direct or VID format and allows
  setting of different formats on rails 1 and 2. For VID the following
  protocols are available: VR13 mode with 5-mV DAC; VR13 mode with
  10-mV DAC, IMVP9 mode with 5-mV DAC.
Signed-off-by: Vadim Pasternak <vadimp@nvidia.com>
Link: https://lore.kernel.org/r/20200926204957.10268-2-vadimp@nvidia.com
[groeck: Cleaned up a couple of error returns; fixed up API changes]
Signed-off-by: Guenter Roeck <linux@roeck-us.net>

Documentation/hwmon/mp2975.rst

+.. SPDX-License-Identifier: GPL-2.0
+
+Kernel driver mp2975
+====================
+
+Supported chips:
+
+  * MPS MP12254
+
+    Prefix: 'mp2975'
+
+Author:
+
+	Vadim Pasternak <vadimp@nvidia.com>
+
+Description
+-----------
+
+This driver implements support for Monolithic Power Systems, Inc. (MPS)
+vendor dual-loop, digital, multi-phase controller MP2975.
+
+This device:
+- Supports up to two power rail.
+- Provides 8 pulse-width modulations (PWMs), and can be configured up
+  to 8-phase operation for rail 1 and up to 4-phase operation for rail
+  2.
+- Supports two pages 0 and 1 for telemetry and also pages 2 and 3 for
+  configuration.
+- Can configured VOUT readout in direct or VID format and allows
+  setting of different formats on rails 1 and 2. For VID the following
+  protocols are available: VR13 mode with 5-mV DAC; VR13 mode with
+  10-mV DAC, IMVP9 mode with 5-mV DAC.
+
+Device supports:
+- SVID interface.
+- AVSBus interface.
+
+Device complaint with:
+- PMBus rev 1.3 interface.
+
+Device supports direct format for reading output current, output voltage,
+input and output power and temperature.
+Device supports linear format for reading input voltage and input power.
+Device supports VID and direct formats for reading output voltage.
+The below VID modes are supported: VR12, VR13, IMVP9.
+
+The driver provides the next attributes for the current:
+- for current in: input, maximum alarm;
+- for current out input, maximum alarm and highest values;
+- for phase current: input and label.
+attributes.
+The driver exports the following attributes via the 'sysfs' files, where
+- 'n' is number of telemetry pages (from 1 to 2);
+- 'k' is number of configured phases (from 1 to 8);
+- indexes 1, 1*n for "iin";
+- indexes n+1, n+2 for "iout";
+- indexes 2*n+1 ... 2*n + k for phases.
+
+**curr[1-{2n}]_alarm**
+
+**curr[{n+1}-{n+2}]_highest**
+
+**curr[1-{2n+k}]_input**
+
+**curr[1-{2n+k}]_label**
+
+The driver provides the next attributes for the voltage:
+- for voltage in: input, high critical threshold, high critical alarm, all only
+  from page 0;
+- for voltage out: input, low and high critical thresholds, low and high
+  critical alarms, from pages 0 and 1;
+The driver exports the following attributes via the 'sysfs' files, where
+- 'n' is number of telemetry pages (from 1 to 2);
+- indexes 1 for "iin";
+- indexes n+1, n+2 for "vout";
+
+**in[1-{2n+1}]_crit**
+
+**in[1-{2n+1}]_crit_alarm**
+
+**in[1-{2n+1}]_input**
+
+**in[1-{2n+1}]_label**
+
+**in[2-{n+1}]_lcrit**
+
+**in[2-{n+1}1_lcrit_alarm**
+
+The driver provides the next attributes for the power:
+- for power in alarm and input.
+- for power out: highest and input.
+The driver exports the following attributes via the 'sysfs' files, where
+- 'n' is number of telemetry pages (from 1 to 2);
+- indexes 1 for "pin";
+- indexes n+1, n+2 for "pout";
+
+**power1_alarm**
+
+**power[2-{n+1}]_highest**
+
+**power[1-{2n+1}]_input**
+
+**power[1-{2n+1}]_label**
+
+The driver provides the next attributes for the temperature (only from page 0):
+
+
+**temp1_crit**
+
+**temp1_crit_alarm**
+
+**temp1_input**
+
+**temp1_max**
+
+**temp1_max_alarm**

drivers/hwmon/pmbus/Kconfig

@@ -211,6 +211,15 @@ config SENSORS_MAX8688
 	  This driver can also be built as a module. If so, the module will
 	  be called max8688.
 
+config SENSORS_MP2975
+	tristate "MPS MP2975"
+	help
+	  If you say yes here you get hardware monitoring support for MPS
+	  MP2975 Dual Loop Digital Multi-Phase Controller.
+
+	  This driver can also be built as a module. If so, the module will
+	  be called mp2975.
+
 config SENSORS_PXE1610
 	tristate "Infineon PXE1610"
 	help

drivers/hwmon/pmbus/Makefile

@@ -24,6 +24,7 @@ obj-$(CONFIG_SENSORS_MAX20751)	+= max20751.o
 obj-$(CONFIG_SENSORS_MAX31785)	+= max31785.o
 obj-$(CONFIG_SENSORS_MAX34440)	+= max34440.o
 obj-$(CONFIG_SENSORS_MAX8688)	+= max8688.o
+obj-$(CONFIG_SENSORS_MP2975)	+= mp2975.o
 obj-$(CONFIG_SENSORS_PXE1610)	+= pxe1610.o
 obj-$(CONFIG_SENSORS_TPS40422)	+= tps40422.o
 obj-$(CONFIG_SENSORS_TPS53679)	+= tps53679.o