hwmon: Add Baikal-T1 PVT sensor driver

.. SPDX-License-Identifier: GPL-2.0-only

Kernel driver bt1-pvt

=====================

Supported chips:

  * Baikal-T1 PVT sensor (in SoC)

    Prefix: 'bt1-pvt'

    Addresses scanned: -

    Datasheet: Provided by BAIKAL ELECTRONICS upon request and under NDA

Authors:

    Maxim Kaurkin <maxim.kaurkin@baikalelectronics.ru>

    Serge Semin <Sergey.Semin@baikalelectronics.ru>

Description

-----------

This driver implements support for the hardware monitoring capabilities of the

embedded into Baikal-T1 process, voltage and temperature sensors. PVT IP-core

consists of one temperature and four voltage sensors, which can be used to

monitor the chip internal environment like heating, supply voltage and

transistors performance. The driver can optionally provide the hwmon alarms

for each sensor the PVT controller supports. The alarms functionality is made

compile-time configurable due to the hardware interface implementation

peculiarity, which is connected with an ability to convert data from only one

sensor at a time. Additional limitation is that the controller performs the

thresholds checking synchronously with the data conversion procedure. Due to

these in order to have the hwmon alarms automatically detected the driver code

must switch from one sensor to another, read converted data and manually check

the threshold status bits. Depending on the measurements timeout settings

(update_interval sysfs node value) this design may cause additional burden on

the system performance. So in case if alarms are unnecessary in your system

design it's recommended to have them disabled to prevent the PVT IRQs being

periodically raised to get the data cache/alarms status up to date. By default

in alarm-less configuration the data conversion is performed by the driver

on demand when read operation is requested via corresponding _input-file.

Temperature Monitoring

----------------------

Temperature is measured with 10-bit resolution and reported in millidegree

Celsius. The driver performs all the scaling by itself therefore reports true

temperatures that don't need any user-space adjustments. While the data

translation formulae isn't linear, which gives us non-linear discreteness,

it's close to one, but giving a bit better accuracy for higher temperatures.

The temperature input is mapped as follows (the last column indicates the input

ranges)::

	temp1: CPU embedded diode	-48.38C - +147.438C

In case if the alarms kernel config is enabled in the driver the temperature input

has associated min and max limits which trigger an alarm when crossed.

Voltage Monitoring

------------------

The voltage inputs are also sampled with 10-bit resolution and reported in

millivolts. But in this case the data translation formulae is linear, which

provides a constant measurements discreteness. The data scaling is also

performed by the driver, so returning true millivolts. The voltage inputs are

mapped as follows (the last column indicates the input ranges)::

	in0: VDD		(processor core)		0.62V - 1.168V

	in1: Low-Vt		(low voltage threshold)		0.62V - 1.168V

	in2: High-Vt		(high voltage threshold)	0.62V - 1.168V

	in3: Standard-Vt	(standard voltage threshold)	0.62V - 1.168V

In case if the alarms config is enabled in the driver the voltage inputs

have associated min and max limits which trigger an alarm when crossed.

Sysfs Attributes

----------------

Following is a list of all sysfs attributes that the driver provides, their

permissions and a short description:

=============================== ======= =======================================

Name				Perm	Description

=============================== ======= =======================================

update_interval			RW	Measurements update interval per

					sensor.

temp1_type			RO	Sensor type (always 1 as CPU embedded

					diode).

temp1_label			RO	CPU Core Temperature sensor.

temp1_input			RO	Measured temperature in millidegree

					Celsius.

temp1_min			RW	Low limit for temp input.

temp1_max			RW	High limit for temp input.

temp1_min_alarm			RO	Temperature input alarm. Returns 1 if

					temperature input went below min limit,

					0 otherwise.

temp1_max_alarm			RO	Temperature input alarm. Returns 1 if

					temperature input went above max limit,

					0 otherwise.

temp1_offset			RW	Temperature offset in millidegree

					Celsius which is added to the

					temperature reading by the chip. It can

					be used to manually adjust the

					temperature measurements within 7.130

					degrees Celsius.

in[0-3]_label			RO	CPU Voltage sensor (either core or

					low/high/standard thresholds).

in[0-3]_input			RO	Measured voltage in millivolts.

in[0-3]_min			RW	Low limit for voltage input.

in[0-3]_max			RW	High limit for voltage input.

in[0-3]_min_alarm		RO	Voltage input alarm. Returns 1 if

					voltage input went below min limit,

					0 otherwise.

in[0-3]_max_alarm		RO	Voltage input alarm. Returns 1 if

					voltage input went above max limit,

					0 otherwise.

=============================== ======= =======================================

   asc7621

   aspeed-pwm-tacho

   bel-pfe

   bt1-pvt

   coretemp

   da9052

   da9055

	  This driver can also be built as a module. If so, the module

	  will be called atxp1.

config SENSORS_BT1_PVT

	tristate "Baikal-T1 Process, Voltage, Temperature sensor driver"

	depends on MIPS_BAIKAL_T1 || COMPILE_TEST

	help

	  If you say yes here you get support for Baikal-T1 PVT sensor

	  embedded into the SoC.

	  This driver can also be built as a module. If so, the module will be

	  called bt1-pvt.

config SENSORS_BT1_PVT_ALARMS

	bool "Enable Baikal-T1 PVT sensor alarms"

	depends on SENSORS_BT1_PVT

	help

	  Baikal-T1 PVT IP-block provides threshold registers for each

	  supported sensor. But the corresponding interrupts might be

	  generated by the thresholds comparator only in synchronization with

	  a data conversion. Additionally there is only one sensor data can

	  be converted at a time. All of these makes the interface impossible

	  to be used for the hwmon alarms implementation without periodic

	  switch between the PVT sensors. By default the data conversion is

	  performed on demand from the user-space. If this config is enabled

	  the data conversion will be periodically performed and the data will be

	  saved in the internal driver cache.

config SENSORS_DRIVETEMP

	tristate "Hard disk drives with temperature sensors"

	depends on SCSI && ATA

obj-$(CONFIG_SENSORS_ASPEED)	+= aspeed-pwm-tacho.o

obj-$(CONFIG_SENSORS_ATXP1)	+= atxp1.o

obj-$(CONFIG_SENSORS_AXI_FAN_CONTROL) += axi-fan-control.o

obj-$(CONFIG_SENSORS_BT1_PVT)	+= bt1-pvt.o

obj-$(CONFIG_SENSORS_CORETEMP)	+= coretemp.o

obj-$(CONFIG_SENSORS_DA9052_ADC)+= da9052-hwmon.o

obj-$(CONFIG_SENSORS_DA9055)+= da9055-hwmon.o