1.. SPDX-License-Identifier: GPL-2.0-only
  2
  3Kernel driver bt1-pvt
  4=====================
  5
  6Supported chips:
  7
  8  * Baikal-T1 PVT sensor (in SoC)
  9
 10    Prefix: 'bt1-pvt'
 11
 12    Addresses scanned: -
 13
 14    Datasheet: Provided by BAIKAL ELECTRONICS upon request and under NDA
 15
 16Authors:
 17    Maxim Kaurkin <maxim.kaurkin@baikalelectronics.ru>
 18    Serge Semin <Sergey.Semin@baikalelectronics.ru>
 19
 20Description
 21-----------
 22
 23This driver implements support for the hardware monitoring capabilities of the
 24embedded into Baikal-T1 process, voltage and temperature sensors. PVT IP-core
 25consists of one temperature and four voltage sensors, which can be used to
 26monitor the chip internal environment like heating, supply voltage and
 27transistors performance. The driver can optionally provide the hwmon alarms
 28for each sensor the PVT controller supports. The alarms functionality is made
 29compile-time configurable due to the hardware interface implementation
 30peculiarity, which is connected with an ability to convert data from only one
 31sensor at a time. Additional limitation is that the controller performs the
 32thresholds checking synchronously with the data conversion procedure. Due to
 33these in order to have the hwmon alarms automatically detected the driver code
 34must switch from one sensor to another, read converted data and manually check
 35the threshold status bits. Depending on the measurements timeout settings
 36(update_interval sysfs node value) this design may cause additional burden on
 37the system performance. So in case if alarms are unnecessary in your system
 38design it's recommended to have them disabled to prevent the PVT IRQs being
 39periodically raised to get the data cache/alarms status up to date. By default
 40in alarm-less configuration the data conversion is performed by the driver
 41on demand when read operation is requested via corresponding _input-file.
 42
 43Temperature Monitoring
 44----------------------
 45
 46Temperature is measured with 10-bit resolution and reported in millidegree
 47Celsius. The driver performs all the scaling by itself therefore reports true
 48temperatures that don't need any user-space adjustments. While the data
 49translation formulae isn't linear, which gives us non-linear discreteness,
 50it's close to one, but giving a bit better accuracy for higher temperatures.
 51The temperature input is mapped as follows (the last column indicates the input
 52ranges)::
 53
 54	temp1: CPU embedded diode	-48.38C - +147.438C
 55
 56In case if the alarms kernel config is enabled in the driver the temperature input
 57has associated min and max limits which trigger an alarm when crossed.
 58
 59Voltage Monitoring
 60------------------
 61
 62The voltage inputs are also sampled with 10-bit resolution and reported in
 63millivolts. But in this case the data translation formulae is linear, which
 64provides a constant measurements discreteness. The data scaling is also
 65performed by the driver, so returning true millivolts. The voltage inputs are
 66mapped as follows (the last column indicates the input ranges)::
 67
 68	in0: VDD		(processor core)		0.62V - 1.168V
 69	in1: Low-Vt		(low voltage threshold)		0.62V - 1.168V
 70	in2: High-Vt		(high voltage threshold)	0.62V - 1.168V
 71	in3: Standard-Vt	(standard voltage threshold)	0.62V - 1.168V
 72
 73In case if the alarms config is enabled in the driver the voltage inputs
 74have associated min and max limits which trigger an alarm when crossed.
 75
 76Sysfs Attributes
 77----------------
 78
 79Following is a list of all sysfs attributes that the driver provides, their
 80permissions and a short description:
 81
 82=============================== ======= =======================================
 83Name				Perm	Description
 84=============================== ======= =======================================
 85update_interval			RW	Measurements update interval per
 86					sensor.
 87temp1_type			RO	Sensor type (always 1 as CPU embedded
 88					diode).
 89temp1_label			RO	CPU Core Temperature sensor.
 90temp1_input			RO	Measured temperature in millidegree
 91					Celsius.
 92temp1_min			RW	Low limit for temp input.
 93temp1_max			RW	High limit for temp input.
 94temp1_min_alarm			RO	Temperature input alarm. Returns 1 if
 95					temperature input went below min limit,
 96					0 otherwise.
 97temp1_max_alarm			RO	Temperature input alarm. Returns 1 if
 98					temperature input went above max limit,
 99					0 otherwise.
100temp1_offset			RW	Temperature offset in millidegree
101					Celsius which is added to the
102					temperature reading by the chip. It can
103					be used to manually adjust the
104					temperature measurements within 7.130
105					degrees Celsius.
106in[0-3]_label			RO	CPU Voltage sensor (either core or
107					low/high/standard thresholds).
108in[0-3]_input			RO	Measured voltage in millivolts.
109in[0-3]_min			RW	Low limit for voltage input.
110in[0-3]_max			RW	High limit for voltage input.
111in[0-3]_min_alarm		RO	Voltage input alarm. Returns 1 if
112					voltage input went below min limit,
113					0 otherwise.
114in[0-3]_max_alarm		RO	Voltage input alarm. Returns 1 if
115					voltage input went above max limit,
116					0 otherwise.
117=============================== ======= =======================================