1Kernel driver adt7475
2=====================
3
4Supported chips:
5
6  * Analog Devices ADT7473
7
8    Prefix: 'adt7473'
9
10    Addresses scanned: I2C 0x2C, 0x2D, 0x2E
11
12    Datasheet: Publicly available at the On Semiconductors website
13
14  * Analog Devices ADT7475
15
16    Prefix: 'adt7475'
17
18    Addresses scanned: I2C 0x2E
19
20    Datasheet: Publicly available at the On Semiconductors website
21
22  * Analog Devices ADT7476
23
24    Prefix: 'adt7476'
25
26    Addresses scanned: I2C 0x2C, 0x2D, 0x2E
27
28    Datasheet: Publicly available at the On Semiconductors website
29
30  * Analog Devices ADT7490
31
32    Prefix: 'adt7490'
33
34    Addresses scanned: I2C 0x2C, 0x2D, 0x2E
35
36    Datasheet: Publicly available at the On Semiconductors website
37
38Authors:
39	- Jordan Crouse
40	- Hans de Goede
41	- Darrick J. Wong (documentation)
42	- Jean Delvare
43
44
45Description
46-----------
47
48This driver implements support for the Analog Devices ADT7473, ADT7475,
49ADT7476 and ADT7490 chip family. The ADT7473 and ADT7475 differ only in
50minor details. The ADT7476 has additional features, including extra voltage
51measurement inputs and VID support. The ADT7490 also has additional
52features, including extra voltage measurement inputs and PECI support. All
53the supported chips will be collectively designed by the name "ADT747x" in
54the rest of this document.
55
56The ADT747x uses the 2-wire interface compatible with the SMBus 2.0
57specification. Using an analog to digital converter it measures three (3)
58temperatures and two (2) or more voltages. It has four (4) 16-bit counters
59for measuring fan speed. There are three (3) PWM outputs that can be used
60to control fan speed.
61
62A sophisticated control system for the PWM outputs is designed into the
63ADT747x that allows fan speed to be adjusted automatically based on any of the
64three temperature sensors. Each PWM output is individually adjustable and
65programmable. Once configured, the ADT747x will adjust the PWM outputs in
66response to the measured temperatures without further host intervention.
67This feature can also be disabled for manual control of the PWM's.
68
69Each of the measured inputs (voltage, temperature, fan speed) has
70corresponding high/low limit values. The ADT747x will signal an ALARM if
71any measured value exceeds either limit.
72
73The ADT747x samples all inputs continuously. The driver will not read
74the registers more often than once every other second. Further,
75configuration data is only read once per minute.
76
77Chip Differences Summary
78------------------------
79
80ADT7473:
81  * 2 voltage inputs
82  * system acoustics optimizations (not implemented)
83
84ADT7475:
85  * 2 voltage inputs
86
87ADT7476:
88  * 5 voltage inputs
89  * VID support
90
91ADT7490:
92  * 6 voltage inputs
93  * 1 Imon input (not implemented)
94  * PECI support (not implemented)
95  * 2 GPIO pins (not implemented)
96  * system acoustics optimizations (not implemented)
97
98Sysfs Mapping
99-------------
100
101==== =========== =========== ========= ==========
102in   ADT7490     ADT7476     ADT7475   ADT7473
103==== =========== =========== ========= ==========
104in0  2.5VIN (22) 2.5VIN (22) -         -
105in1  VCCP   (23) VCCP   (23) VCCP (14) VCCP (14)
106in2  VCC    (4)  VCC    (4)  VCC  (4)  VCC  (3)
107in3  5VIN   (20) 5VIN   (20)
108in4  12VIN  (21) 12VIN  (21)
109in5  VTT    (8)
110==== =========== =========== ========= ==========
111
112Special Features
113----------------
114
115The ADT747x has a 10-bit ADC and can therefore measure temperatures
116with a resolution of 0.25 degree Celsius. Temperature readings can be
117configured either for two's complement format or "Offset 64" format,
118wherein 64 is subtracted from the raw value to get the temperature value.
119
120The datasheet is very detailed and describes a procedure for determining
121an optimal configuration for the automatic PWM control.
122
123Fan Speed Control
124-----------------
125
126The driver exposes two trip points per PWM channel.
127
128- point1: Set the PWM speed at the lower temperature bound
129- point2: Set the PWM speed at the higher temperature bound
130
131The ADT747x will scale the PWM linearly between the lower and higher PWM
132speed when the temperature is between the two temperature boundaries.
133Temperature boundaries are associated to temperature channels rather than
134PWM outputs, and a given PWM output can be controlled by several temperature
135channels. As a result, the ADT747x may compute more than one PWM value
136for a channel at a given time, in which case the maximum value (fastest
137fan speed) is applied. PWM values range from 0 (off) to 255 (full speed).
138
139Fan speed may be set to maximum when the temperature sensor associated with
140the PWM control exceeds temp#_max.
141
142At Tmin - hysteresis the PWM output can either be off (0% duty cycle) or at the
143minimum (i.e. auto_point1_pwm). This behaviour can be configured using the
144`pwm[1-*]_stall_disable sysfs attribute`. A value of 0 means the fans will shut
145off. A value of 1 means the fans will run at auto_point1_pwm.
146
147The responsiveness of the ADT747x to temperature changes can be configured.
148This allows smoothing of the fan speed transition. To set the transition time
149set the value in ms in the `temp[1-*]_smoothing` sysfs attribute.
150
151Notes
152-----
153
154The nVidia binary driver presents an ADT7473 chip via an on-card i2c bus.
155Unfortunately, they fail to set the i2c adapter class, so this driver may
156fail to find the chip until the nvidia driver is patched.
157