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hwmon: (nct6775) Add support for pwm, pwm_mode, and pwm_enable
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1Note
2====
3
4This driver supersedes the NCT6775F and NCT6776F support in the W83627EHF
5driver.
6
7Kernel driver NCT6775
8=====================
9
10Supported chips:
11 * Nuvoton NCT6775F/W83667HG-I
12 Prefix: 'nct6775'
13 Addresses scanned: ISA address retrieved from Super I/O registers
14 Datasheet: Available from Nuvoton upon request
15 * Nuvoton NCT6776F
16 Prefix: 'nct6776'
17 Addresses scanned: ISA address retrieved from Super I/O registers
18 Datasheet: Available from Nuvoton upon request
19 * Nuvoton NCT6779D
20 Prefix: 'nct6779'
21 Addresses scanned: ISA address retrieved from Super I/O registers
22 Datasheet: Available from Nuvoton upon request
23
24Authors:
25 Guenter Roeck <linux@roeck-us.net>
26
27Description
28-----------
29
30This driver implements support for the Nuvoton NCT6775F, NCT6776F, and NCT6779D
31super I/O chips.
32
33The chips support up to 25 temperature monitoring sources. Up to 6 of those are
34direct temperature sensor inputs, the others are special sources such as PECI,
35PCH, and SMBUS. Depending on the chip type, 2 to 6 of the temperature sources
36can be monitored and compared against minimum, maximum, and critical
37temperatures. The driver reports up to 10 of the temperatures to the user.
38There are 4 to 5 fan rotation speed sensors, 8 to 15 analog voltage sensors,
39one VID, alarms with beep warnings (control unimplemented), and some automatic
40fan regulation strategies (plus manual fan control mode).
41
42The temperature sensor sources on all chips are configurable. The configured
43source for each of the temperature sensors is provided in tempX_label.
44
45Temperatures are measured in degrees Celsius and measurement resolution is
46either 1 degC or 0.5 degC, depending on the temperature source and
47configuration. An alarm is triggered when the temperature gets higher than
48the high limit; it stays on until the temperature falls below the hysteresis
49value. Alarms are only supported for temp1 to temp6, depending on the chip type.
50
51Fan rotation speeds are reported in RPM (rotations per minute). An alarm is
52triggered if the rotation speed has dropped below a programmable limit. On
53NCT6775F, fan readings can be divided by a programmable divider (1, 2, 4, 8,
5416, 32, 64 or 128) to give the readings more range or accuracy; the other chips
55do not have a fan speed divider. The driver sets the most suitable fan divisor
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56itself; specifically, it increases the divider value each time a fan speed
57reading returns an invalid value, and it reduces it if the fan speed reading
58is lower than optimal. Some fans might not be present because they share pins
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59with other functions.
60
61Voltage sensors (also known as IN sensors) report their values in millivolts.
62An alarm is triggered if the voltage has crossed a programmable minimum
63or maximum limit.
64
65The driver supports automatic fan control mode known as Thermal Cruise.
66In this mode, the chip attempts to keep the measured temperature in a
67predefined temperature range. If the temperature goes out of range, fan
68is driven slower/faster to reach the predefined range again.
69
70The mode works for fan1-fan5.
71
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72sysfs attributes
73----------------
74
75pwm[1-5] - this file stores PWM duty cycle or DC value (fan speed) in range:
76 0 (lowest speed) to 255 (full)
77
78pwm[1-5]_enable - this file controls mode of fan/temperature control:
79 * 0 Fan control disabled (fans set to maximum speed)
80 * 1 Manual mode, write to pwm[0-5] any value 0-255
81 * 2 "Thermal Cruise" mode
82 * 3 "Fan Speed Cruise" mode
83 * 4 "Smart Fan III" mode (NCT6775F only)
84 * 5 "Smart Fan IV" mode
85
86pwm[1-5]_mode - controls if output is PWM or DC level
87 * 0 DC output
88 * 1 PWM output
89
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90Usage Notes
91-----------
92
93On various ASUS boards with NCT6776F, it appears that CPUTIN is not really
94connected to anything and floats, or that it is connected to some non-standard
95temperature measurement device. As a result, the temperature reported on CPUTIN
96will not reflect a usable value. It often reports unreasonably high
97temperatures, and in some cases the reported temperature declines if the actual
98temperature increases (similar to the raw PECI temperature value - see PECI
99specification for details). CPUTIN should therefore be be ignored on ASUS
100boards. The CPU temperature on ASUS boards is reported from PECI 0.