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1.. SPDX-License-Identifier: GPL-2.02 3Kernel driver max318274======================5 6Supported chips:7 8 * Maxim MAX318279 10 Prefix: 'max31827'11 12 Addresses scanned: I2C 0x40 - 0x5f13 14 Datasheet: Publicly available at the Analog Devices website15 16 * Maxim MAX3182817 18 Prefix: 'max31828'19 20 Addresses scanned: I2C 0x40 - 0x5f21 22 Datasheet: Publicly available at the Analog Devices website23 24 * Maxim MAX3182925 26 Prefix: 'max31829'27 28 Addresses scanned: I2C 0x40 - 0x5f29 30 Datasheet: Publicly available at the Analog Devices website31 32 33Authors:34 - Daniel Matyas <daniel.matyas@analog.com>35 36Description37-----------38 39The chips supported by this driver are quite similar. The only difference40between them is found in the default power-on behaviour of the chips. While the41MAX31827's fault queue is set to 1, the other two chip's fault queue is set to424. Besides this, the MAX31829's alarm active state is high, while the other two43chip's alarms are active on low. It is important to note that the chips can be44configured to operate in the same manner with 1 write operation to the45configuration register. From here on, we will refer to all these chips as46MAX31827.47 48MAX31827 implements a temperature sensor with a 6 WLP packaging scheme. This49sensor measures the temperature of the chip itself.50 51MAX31827 has low and over temperature alarms with an effective value and a52hysteresis value: -40 and -30 degrees for under temperature alarm and +100 and53+90 degrees for over temperature alarm.54 55The alarm can be configured in comparator and interrupt mode from the56devicetree. In Comparator mode, the OT/UT status bits have a value of 1 when the57temperature rises above the TH value or falls below TL, which is also subject to58the Fault Queue selection. OT status returns to 0 when the temperature drops59below the TH_HYST value or when shutdown mode is entered. Similarly, UT status60returns to 0 when the temperature rises above TL_HYST value or when shutdown61mode is entered.62 63In interrupt mode exceeding TH also sets OT status to 1, which remains set until64a read operation is performed on the configuration/status register (max or min65attribute); at this point, it returns to 0. Once OT status is set to 1 from66exceeding TH and reset, it is set to 1 again only when the temperature drops67below TH_HYST. The output remains asserted until it is reset by a read. It is68set again if the temperature rises above TH, and so on. The same logic applies69to the operation of the UT status bit.70 71Putting the MAX31827 into shutdown mode also resets the OT/UT status bits. Note72that if the mode is changed while OT/UT status bits are set, an OT/UT status73reset may be required before it begins to behave normally. To prevent this,74it is recommended to perform a read of the configuration/status register to75clear the status bits before changing the operating mode.76 77The conversions can be manual with the one-shot functionality and automatic with78a set frequency. When powered on, the chip measures temperatures with 1 conv/s.79The conversion rate can be modified with update_interval attribute of the chip.80Conversion/second = 1/update_interval. Thus, the available options according to81the data sheet are:82 83- 64000 (ms) = 1 conv/64 sec84- 32000 (ms) = 1 conv/32 sec85- 16000 (ms) = 1 conv/16 sec86- 4000 (ms) = 1 conv/4 sec87- 1000 (ms) = 1 conv/sec (default)88- 250 (ms) = 4 conv/sec89- 125 (ms) = 8 conv/sec90 91Enabling the device when it is already enabled has the side effect of setting92the conversion frequency to 1 conv/s. The conversion time varies depending on93the resolution.94 95The conversion time doubles with every bit of increased resolution. The96available resolutions are:97 98- 8 bit -> 8.75 ms conversion time99- 9 bit -> 17.5 ms conversion time100- 10 bit -> 35 ms conversion time101- 12 bit (default) -> 140 ms conversion time102 103There is a temp1_resolution attribute which indicates the unit change in the104input temperature in milli-degrees C.105 106- 1000 mC -> 8 bit107- 500 mC -> 9 bit108- 250 mC -> 10 bit109- 62 mC -> 12 bit (default) - actually this is 62.5, but the fil returns 62110 111When chip is in shutdown mode and a read operation is requested, one-shot is112triggered, the device waits for <conversion time> ms, and only after that is113the temperature value register read. Note that the conversion times are rounded114up to the nearest possible integer.115 116The LSB of the temperature values is 0.0625 degrees Celsius, but the values of117the temperatures are displayed in milli-degrees. This means, that some data is118lost. The step between 2 consecutive values is 62 or 63. This effect can be seen119in the writing of alarm values too. For positive numbers the user-input value120will always be rounded down to the nearest possible value, for negative numbers121the user-input will always be rounded up to the nearest possible value.122 123Bus timeout resets the I2C-compatible interface when SCL is low for more than12430ms (nominal).125 126Alarm polarity determines if the active state of the alarm is low or high. The127behavior for both settings is dependent on the Fault Queue setting. The ALARM128pin is an open-drain output and requires a pullup resistor to operate.129 130The Fault Queue bits select how many consecutive temperature faults must occur131before overtemperature or undertemperature faults are indicated in the132corresponding status bits.133 134PEC Support135-----------136 137When reading a register value, the PEC byte is computed and sent by the chip.138 139PEC on word data transaction respresents a signifcant increase in bandwitdh140usage (+33% for both write and reads) in normal conditions.141 142Since this operation implies there will be an extra delay to each143transaction, PEC can be disabled or enabled through sysfs.144Just write 1 to the "pec" file for enabling PEC and 0 for disabling it.145