| xj | b04a402 | 2021-11-25 15:01:52 +0800 | [diff] [blame] | 1 | Kernel driver adt7475 |
| 2 | ===================== |
| 3 | |
| 4 | Supported chips: |
| 5 | * Analog Devices ADT7473 |
| 6 | Prefix: 'adt7473' |
| 7 | Addresses scanned: I2C 0x2C, 0x2D, 0x2E |
| 8 | Datasheet: Publicly available at the On Semiconductors website |
| 9 | * Analog Devices ADT7475 |
| 10 | Prefix: 'adt7475' |
| 11 | Addresses scanned: I2C 0x2E |
| 12 | Datasheet: Publicly available at the On Semiconductors website |
| 13 | * Analog Devices ADT7476 |
| 14 | Prefix: 'adt7476' |
| 15 | Addresses scanned: I2C 0x2C, 0x2D, 0x2E |
| 16 | Datasheet: Publicly available at the On Semiconductors website |
| 17 | * Analog Devices ADT7490 |
| 18 | Prefix: 'adt7490' |
| 19 | Addresses scanned: I2C 0x2C, 0x2D, 0x2E |
| 20 | Datasheet: Publicly available at the On Semiconductors website |
| 21 | |
| 22 | Authors: |
| 23 | Jordan Crouse |
| 24 | Hans de Goede |
| 25 | Darrick J. Wong (documentation) |
| 26 | Jean Delvare |
| 27 | |
| 28 | |
| 29 | Description |
| 30 | ----------- |
| 31 | |
| 32 | This driver implements support for the Analog Devices ADT7473, ADT7475, |
| 33 | ADT7476 and ADT7490 chip family. The ADT7473 and ADT7475 differ only in |
| 34 | minor details. The ADT7476 has additional features, including extra voltage |
| 35 | measurement inputs and VID support. The ADT7490 also has additional |
| 36 | features, including extra voltage measurement inputs and PECI support. All |
| 37 | the supported chips will be collectively designed by the name "ADT747x" in |
| 38 | the rest of this document. |
| 39 | |
| 40 | The ADT747x uses the 2-wire interface compatible with the SMBus 2.0 |
| 41 | specification. Using an analog to digital converter it measures three (3) |
| 42 | temperatures and two (2) or more voltages. It has four (4) 16-bit counters |
| 43 | for measuring fan speed. There are three (3) PWM outputs that can be used |
| 44 | to control fan speed. |
| 45 | |
| 46 | A sophisticated control system for the PWM outputs is designed into the |
| 47 | ADT747x that allows fan speed to be adjusted automatically based on any of the |
| 48 | three temperature sensors. Each PWM output is individually adjustable and |
| 49 | programmable. Once configured, the ADT747x will adjust the PWM outputs in |
| 50 | response to the measured temperatures without further host intervention. |
| 51 | This feature can also be disabled for manual control of the PWM's. |
| 52 | |
| 53 | Each of the measured inputs (voltage, temperature, fan speed) has |
| 54 | corresponding high/low limit values. The ADT747x will signal an ALARM if |
| 55 | any measured value exceeds either limit. |
| 56 | |
| 57 | The ADT747x samples all inputs continuously. The driver will not read |
| 58 | the registers more often than once every other second. Further, |
| 59 | configuration data is only read once per minute. |
| 60 | |
| 61 | Chip Differences Summary |
| 62 | ------------------------ |
| 63 | |
| 64 | ADT7473: |
| 65 | * 2 voltage inputs |
| 66 | * system acoustics optimizations (not implemented) |
| 67 | |
| 68 | ADT7475: |
| 69 | * 2 voltage inputs |
| 70 | |
| 71 | ADT7476: |
| 72 | * 5 voltage inputs |
| 73 | * VID support |
| 74 | |
| 75 | ADT7490: |
| 76 | * 6 voltage inputs |
| 77 | * 1 Imon input (not implemented) |
| 78 | * PECI support (not implemented) |
| 79 | * 2 GPIO pins (not implemented) |
| 80 | * system acoustics optimizations (not implemented) |
| 81 | |
| 82 | Special Features |
| 83 | ---------------- |
| 84 | |
| 85 | The ADT747x has a 10-bit ADC and can therefore measure temperatures |
| 86 | with a resolution of 0.25 degree Celsius. Temperature readings can be |
| 87 | configured either for two's complement format or "Offset 64" format, |
| 88 | wherein 64 is subtracted from the raw value to get the temperature value. |
| 89 | |
| 90 | The datasheet is very detailed and describes a procedure for determining |
| 91 | an optimal configuration for the automatic PWM control. |
| 92 | |
| 93 | Fan Speed Control |
| 94 | ----------------- |
| 95 | |
| 96 | The driver exposes two trip points per PWM channel. |
| 97 | |
| 98 | point1: Set the PWM speed at the lower temperature bound |
| 99 | point2: Set the PWM speed at the higher temperature bound |
| 100 | |
| 101 | The ADT747x will scale the PWM linearly between the lower and higher PWM |
| 102 | speed when the temperature is between the two temperature boundaries. |
| 103 | Temperature boundaries are associated to temperature channels rather than |
| 104 | PWM outputs, and a given PWM output can be controlled by several temperature |
| 105 | channels. As a result, the ADT747x may compute more than one PWM value |
| 106 | for a channel at a given time, in which case the maximum value (fastest |
| 107 | fan speed) is applied. PWM values range from 0 (off) to 255 (full speed). |
| 108 | |
| 109 | Fan speed may be set to maximum when the temperature sensor associated with |
| 110 | the PWM control exceeds temp#_max. |
| 111 | |
| 112 | At Tmin - hysteresis the PWM output can either be off (0% duty cycle) or at the |
| 113 | minimum (i.e. auto_point1_pwm). This behaviour can be configured using the |
| 114 | pwm[1-*]_stall_disable sysfs attribute. A value of 0 means the fans will shut |
| 115 | off. A value of 1 means the fans will run at auto_point1_pwm. |
| 116 | |
| 117 | The responsiveness of the ADT747x to temperature changes can be configured. |
| 118 | This allows smoothing of the fan speed transition. To set the transition time |
| 119 | set the value in ms in the temp[1-*]_smoothing sysfs attribute. |
| 120 | |
| 121 | Notes |
| 122 | ----- |
| 123 | |
| 124 | The nVidia binary driver presents an ADT7473 chip via an on-card i2c bus. |
| 125 | Unfortunately, they fail to set the i2c adapter class, so this driver may |
| 126 | fail to find the chip until the nvidia driver is patched. |