.. SPDX-License-Identifier: GPL-2.0-only
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Kernel driver bt1-pvt
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=====================
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Supported chips:
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* Baikal-T1 PVT sensor (in SoC)
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Prefix: 'bt1-pvt'
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Addresses scanned: -
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Datasheet: Provided by BAIKAL ELECTRONICS upon request and under NDA
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Authors:
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Maxim Kaurkin <maxim.kaurkin@baikalelectronics.ru>
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Serge Semin <Sergey.Semin@baikalelectronics.ru>
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Description
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-----------
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This driver implements support for the hardware monitoring capabilities of the
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embedded into Baikal-T1 process, voltage and temperature sensors. PVT IP-core
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consists of one temperature and four voltage sensors, which can be used to
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monitor the chip internal environment like heating, supply voltage and
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transistors performance. The driver can optionally provide the hwmon alarms
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for each sensor the PVT controller supports. The alarms functionality is made
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compile-time configurable due to the hardware interface implementation
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peculiarity, which is connected with an ability to convert data from only one
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sensor at a time. Additional limitation is that the controller performs the
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thresholds checking synchronously with the data conversion procedure. Due to
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these in order to have the hwmon alarms automatically detected the driver code
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must switch from one sensor to another, read converted data and manually check
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the threshold status bits. Depending on the measurements timeout settings
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(update_interval sysfs node value) this design may cause additional burden on
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the system performance. So in case if alarms are unnecessary in your system
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design it's recommended to have them disabled to prevent the PVT IRQs being
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periodically raised to get the data cache/alarms status up to date. By default
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in alarm-less configuration the data conversion is performed by the driver
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on demand when read operation is requested via corresponding _input-file.
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Temperature Monitoring
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----------------------
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Temperature is measured with 10-bit resolution and reported in millidegree
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Celsius. The driver performs all the scaling by itself therefore reports true
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temperatures that don't need any user-space adjustments. While the data
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translation formulae isn't linear, which gives us non-linear discreteness,
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it's close to one, but giving a bit better accuracy for higher temperatures.
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The temperature input is mapped as follows (the last column indicates the input
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ranges)::
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temp1: CPU embedded diode -48.38C - +147.438C
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In case if the alarms kernel config is enabled in the driver the temperature input
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has associated min and max limits which trigger an alarm when crossed.
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Voltage Monitoring
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------------------
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The voltage inputs are also sampled with 10-bit resolution and reported in
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millivolts. But in this case the data translation formulae is linear, which
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provides a constant measurements discreteness. The data scaling is also
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performed by the driver, so returning true millivolts. The voltage inputs are
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mapped as follows (the last column indicates the input ranges)::
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in0: VDD (processor core) 0.62V - 1.168V
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in1: Low-Vt (low voltage threshold) 0.62V - 1.168V
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in2: High-Vt (high voltage threshold) 0.62V - 1.168V
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in3: Standard-Vt (standard voltage threshold) 0.62V - 1.168V
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In case if the alarms config is enabled in the driver the voltage inputs
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have associated min and max limits which trigger an alarm when crossed.
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Sysfs Attributes
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----------------
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Following is a list of all sysfs attributes that the driver provides, their
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permissions and a short description:
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=============================== ======= =======================================
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Name Perm Description
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=============================== ======= =======================================
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update_interval RW Measurements update interval per
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sensor.
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temp1_type RO Sensor type (always 1 as CPU embedded
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diode).
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temp1_label RO CPU Core Temperature sensor.
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temp1_input RO Measured temperature in millidegree
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Celsius.
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temp1_min RW Low limit for temp input.
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temp1_max RW High limit for temp input.
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temp1_min_alarm RO Temperature input alarm. Returns 1 if
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temperature input went below min limit,
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0 otherwise.
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temp1_max_alarm RO Temperature input alarm. Returns 1 if
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temperature input went above max limit,
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0 otherwise.
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temp1_offset RW Temperature offset in millidegree
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Celsius which is added to the
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temperature reading by the chip. It can
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be used to manually adjust the
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temperature measurements within 7.130
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degrees Celsius.
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in[0-3]_label RO CPU Voltage sensor (either core or
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low/high/standard thresholds).
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in[0-3]_input RO Measured voltage in millivolts.
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in[0-3]_min RW Low limit for voltage input.
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in[0-3]_max RW High limit for voltage input.
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in[0-3]_min_alarm RO Voltage input alarm. Returns 1 if
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voltage input went below min limit,
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0 otherwise.
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in[0-3]_max_alarm RO Voltage input alarm. Returns 1 if
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voltage input went above max limit,
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0 otherwise.
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=============================== ======= =======================================
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