Loading...
1Kernel driver it87
2==================
3
4Supported chips:
5
6 * IT8603E/IT8623E
7
8 Prefix: 'it8603'
9
10 Addresses scanned: from Super I/O config space (8 I/O ports)
11
12 Datasheet: Not publicly available
13
14 * IT8620E
15
16 Prefix: 'it8620'
17
18 Addresses scanned: from Super I/O config space (8 I/O ports)
19
20 * IT8628E
21
22 Prefix: 'it8628'
23
24 Addresses scanned: from Super I/O config space (8 I/O ports)
25
26 Datasheet: Not publicly available
27
28 * IT8705F
29
30 Prefix: 'it87'
31
32 Addresses scanned: from Super I/O config space (8 I/O ports)
33
34 Datasheet: Once publicly available at the ITE website, but no longer
35
36 * IT8712F
37
38 Prefix: 'it8712'
39
40 Addresses scanned: from Super I/O config space (8 I/O ports)
41
42 Datasheet: Once publicly available at the ITE website, but no longer
43
44 * IT8716F/IT8726F
45
46 Prefix: 'it8716'
47
48 Addresses scanned: from Super I/O config space (8 I/O ports)
49
50 Datasheet: Once publicly available at the ITE website, but no longer
51
52 * IT8718F
53
54 Prefix: 'it8718'
55
56 Addresses scanned: from Super I/O config space (8 I/O ports)
57
58 Datasheet: Once publicly available at the ITE website, but no longer
59
60 * IT8720F
61
62 Prefix: 'it8720'
63
64 Addresses scanned: from Super I/O config space (8 I/O ports)
65
66 Datasheet: Not publicly available
67
68 * IT8721F/IT8758E
69
70 Prefix: 'it8721'
71
72 Addresses scanned: from Super I/O config space (8 I/O ports)
73
74 Datasheet: Not publicly available
75
76 * IT8728F
77
78 Prefix: 'it8728'
79
80 Addresses scanned: from Super I/O config space (8 I/O ports)
81
82 Datasheet: Not publicly available
83
84 * IT8732F
85
86 Prefix: 'it8732'
87
88 Addresses scanned: from Super I/O config space (8 I/O ports)
89
90 Datasheet: Not publicly available
91
92 * IT8771E
93
94 Prefix: 'it8771'
95
96 Addresses scanned: from Super I/O config space (8 I/O ports)
97
98 Datasheet: Not publicly available
99
100 * IT8772E
101
102 Prefix: 'it8772'
103
104 Addresses scanned: from Super I/O config space (8 I/O ports)
105
106 Datasheet: Not publicly available
107
108 * IT8781F
109
110 Prefix: 'it8781'
111
112 Addresses scanned: from Super I/O config space (8 I/O ports)
113
114 Datasheet: Not publicly available
115
116 * IT8782F
117
118 Prefix: 'it8782'
119
120 Addresses scanned: from Super I/O config space (8 I/O ports)
121
122 Datasheet: Not publicly available
123
124 * IT8783E/F
125
126 Prefix: 'it8783'
127
128 Addresses scanned: from Super I/O config space (8 I/O ports)
129
130 Datasheet: Not publicly available
131
132 * IT8786E
133
134 Prefix: 'it8786'
135
136 Addresses scanned: from Super I/O config space (8 I/O ports)
137
138 Datasheet: Not publicly available
139
140 * IT8790E
141
142 Prefix: 'it8790'
143
144 Addresses scanned: from Super I/O config space (8 I/O ports)
145
146 Datasheet: Not publicly available
147
148 * IT8792E/IT8795E
149
150 Prefix: 'it8792'
151
152 Addresses scanned: from Super I/O config space (8 I/O ports)
153
154 Datasheet: Not publicly available
155
156 * IT87952E
157
158 Prefix: 'it87952'
159
160 Addresses scanned: from Super I/O config space (8 I/O ports)
161
162 Datasheet: Not publicly available
163
164 * SiS950 [clone of IT8705F]
165
166 Prefix: 'it87'
167
168 Addresses scanned: from Super I/O config space (8 I/O ports)
169
170 Datasheet: No longer be available
171
172
173Authors:
174 - Christophe Gauthron
175 - Jean Delvare <jdelvare@suse.de>
176
177
178Module Parameters
179-----------------
180
181* update_vbat bool
182 0 if vbat should report power on value, 1 if vbat should be updated after
183 each read. Default is 0. On some boards the battery voltage is provided
184 by either the battery or the onboard power supply. Only the first reading
185 at power on will be the actual battery voltage (which the chip does
186 automatically). On other boards the battery voltage is always fed to
187 the chip so can be read at any time. Excessive reading may decrease
188 battery life but no information is given in the datasheet.
189
190* fix_pwm_polarity bool
191 Force PWM polarity to active high (DANGEROUS). Some chips are
192 misconfigured by BIOS - PWM values would be inverted. This option tries
193 to fix this. Please contact your BIOS manufacturer and ask him for fix.
194
195* force_id short, short
196
197 Force multiple chip ID to specified value, separated by ','.
198 For example "force_id=0x8689,0x8633". A value of 0 is ignored
199 for that chip.
200 Note: A single force_id value (e.g. "force_id=0x8689") is used for
201 all chips, to only set the first chip use "force_id=0x8689,0".
202 Should only be used for testing.
203
204* ignore_resource_conflict bool
205
206 Similar to acpi_enforce_resources=lax, but only affects this driver.
207 ACPI resource conflicts are ignored if this parameter is provided and
208 set to 1.
209 Provided since there are reports that system-wide acpi_enfore_resources=lax
210 can result in boot failures on some systems.
211 Note: This is inherently risky since it means that both ACPI and this driver
212 may access the chip at the same time. This can result in race conditions and,
213 worst case, result in unexpected system reboots.
214
215
216Hardware Interfaces
217-------------------
218
219All the chips supported by this driver are LPC Super-I/O chips, accessed
220through the LPC bus (ISA-like I/O ports). The IT8712F additionally has an
221SMBus interface to the hardware monitoring functions. This driver no
222longer supports this interface though, as it is slower and less reliable
223than the ISA access, and was only available on a small number of
224motherboard models.
225
226
227Description
228-----------
229
230This driver implements support for the IT8603E, IT8620E, IT8623E, IT8628E,
231IT8705F, IT8712F, IT8716F, IT8718F, IT8720F, IT8721F, IT8726F, IT8728F, IT8732F,
232IT8758E, IT8771E, IT8772E, IT8781F, IT8782F, IT8783E/F, IT8786E, IT8790E,
233IT8792E/IT8795E, IT87952E and SiS950 chips.
234
235These chips are 'Super I/O chips', supporting floppy disks, infrared ports,
236joysticks and other miscellaneous stuff. For hardware monitoring, they
237include an 'environment controller' with 3 temperature sensors, 3 fan
238rotation speed sensors, 8 voltage sensors, associated alarms, and chassis
239intrusion detection.
240
241The IT8712F and IT8716F additionally feature VID inputs, used to report
242the Vcore voltage of the processor. The early IT8712F have 5 VID pins,
243the IT8716F and late IT8712F have 6. They are shared with other functions
244though, so the functionality may not be available on a given system.
245
246The IT8718F and IT8720F also features VID inputs (up to 8 pins) but the value
247is stored in the Super-I/O configuration space. Due to technical limitations,
248this value can currently only be read once at initialization time, so
249the driver won't notice and report changes in the VID value. The two
250upper VID bits share their pins with voltage inputs (in5 and in6) so you
251can't have both on a given board.
252
253The IT8716F, IT8718F, IT8720F, IT8721F/IT8758E and later IT8712F revisions
254have support for 2 additional fans. The additional fans are supported by the
255driver.
256
257The IT8716F, IT8718F, IT8720F, IT8721F/IT8758E, IT8732F, IT8781F, IT8782F,
258IT8783E/F, and late IT8712F and IT8705F also have optional 16-bit tachometer
259counters for fans 1 to 3. This is better (no more fan clock divider mess) but
260not compatible with the older chips and revisions. The 16-bit tachometer mode
261is enabled by the driver when one of the above chips is detected.
262
263The IT8726F is just bit enhanced IT8716F with additional hardware
264for AMD power sequencing. Therefore the chip will appear as IT8716F
265to userspace applications.
266
267The IT8728F, IT8771E, and IT8772E are considered compatible with the IT8721F,
268until a datasheet becomes available (hopefully.)
269
270The IT8603E/IT8623E is a custom design, hardware monitoring part is similar to
271IT8728F. It only supports 3 fans, 16-bit fan mode, and the full speed mode
272of the fan is not supported (value 0 of pwmX_enable).
273
274The IT8620E and IT8628E are custom designs, hardware monitoring part is similar
275to IT8728F. It only supports 16-bit fan mode. Both chips support up to 6 fans.
276
277The IT8790E, IT8792E/IT8795E and IT87952E support up to 3 fans. 16-bit fan
278mode is always enabled.
279
280The IT8732F supports a closed-loop mode for fan control, but this is not
281currently implemented by the driver.
282
283Temperatures are measured in degrees Celsius. An alarm is triggered once
284when the Overtemperature Shutdown limit is crossed.
285
286Fan rotation speeds are reported in RPM (rotations per minute). An alarm is
287triggered if the rotation speed has dropped below a programmable limit. When
28816-bit tachometer counters aren't used, fan readings can be divided by
289a programmable divider (1, 2, 4 or 8) to give the readings more range or
290accuracy. With a divider of 2, the lowest representable value is around
2912600 RPM. Not all RPM values can accurately be represented, so some rounding
292is done.
293
294Voltage sensors (also known as IN sensors) report their values in volts. An
295alarm is triggered if the voltage has crossed a programmable minimum or
296maximum limit. Note that minimum in this case always means 'closest to
297zero'; this is important for negative voltage measurements. On most chips, all
298voltage inputs can measure voltages between 0 and 4.08 volts, with a resolution
299of 0.016 volt. IT8603E, IT8721F/IT8758E and IT8728F can measure between 0 and
3003.06 volts, with a resolution of 0.012 volt. IT8732F can measure between 0 and
3012.8 volts with a resolution of 0.0109 volt. The battery voltage in8 does not
302have limit registers.
303
304On the IT8603E, IT8620E, IT8628E, IT8721F/IT8758E, IT8732F, IT8781F, IT8782F,
305and IT8783E/F, some voltage inputs are internal and scaled inside the chip:
306* in3 (optional)
307* in7 (optional for IT8781F, IT8782F, and IT8783E/F)
308* in8 (always)
309* in9 (relevant for IT8603E only)
310The driver handles this transparently so user-space doesn't have to care.
311
312The VID lines (IT8712F/IT8716F/IT8718F/IT8720F) encode the core voltage value:
313the voltage level your processor should work with. This is hardcoded by
314the mainboard and/or processor itself. It is a value in volts.
315
316If an alarm triggers, it will remain triggered until the hardware register
317is read at least once. This means that the cause for the alarm may already
318have disappeared! Note that in the current implementation, all hardware
319registers are read whenever any data is read (unless it is less than 1.5
320seconds since the last update). This means that you can easily miss
321once-only alarms.
322
323Out-of-limit readings can also result in beeping, if the chip is properly
324wired and configured. Beeping can be enabled or disabled per sensor type
325(temperatures, voltages and fans.)
326
327The IT87xx only updates its values each 1.5 seconds; reading it more often
328will do no harm, but will return 'old' values.
329
330To change sensor N to a thermistor, 'echo 4 > tempN_type' where N is 1, 2,
331or 3. To change sensor N to a thermal diode, 'echo 3 > tempN_type'.
332Give 0 for unused sensor. Any other value is invalid. To configure this at
333startup, consult lm_sensors's /etc/sensors.conf. (4 = thermistor;
3343 = thermal diode)
335
336
337Fan speed control
338-----------------
339
340The fan speed control features are limited to manual PWM mode. Automatic
341"Smart Guardian" mode control handling is only implemented for older chips
342(see below.) However if you want to go for "manual mode" just write 1 to
343pwmN_enable.
344
345If you are only able to control the fan speed with very small PWM values,
346try lowering the PWM base frequency (pwm1_freq). Depending on the fan,
347it may give you a somewhat greater control range. The same frequency is
348used to drive all fan outputs, which is why pwm2_freq and pwm3_freq are
349read-only.
350
351
352Automatic fan speed control (old interface)
353-------------------------------------------
354
355The driver supports the old interface to automatic fan speed control
356which is implemented by IT8705F chips up to revision F and IT8712F
357chips up to revision G.
358
359This interface implements 4 temperature vs. PWM output trip points.
360The PWM output of trip point 4 is always the maximum value (fan running
361at full speed) while the PWM output of the other 3 trip points can be
362freely chosen. The temperature of all 4 trip points can be freely chosen.
363Additionally, trip point 1 has an hysteresis temperature attached, to
364prevent fast switching between fan on and off.
365
366The chip automatically computes the PWM output value based on the input
367temperature, based on this simple rule: if the temperature value is
368between trip point N and trip point N+1 then the PWM output value is
369the one of trip point N. The automatic control mode is less flexible
370than the manual control mode, but it reacts faster, is more robust and
371doesn't use CPU cycles.
372
373Trip points must be set properly before switching to automatic fan speed
374control mode. The driver will perform basic integrity checks before
375actually switching to automatic control mode.
376
377
378Temperature offset attributes
379-----------------------------
380
381The driver supports temp[1-3]_offset sysfs attributes to adjust the reported
382temperature for thermal diodes or diode-connected thermal transistors.
383If a temperature sensor is configured for thermistors, the attribute values
384are ignored. If the thermal sensor type is Intel PECI, the temperature offset
385must be programmed to the critical CPU temperature.
1Kernel driver it87
2==================
3
4Supported chips:
5
6 * IT8603E/IT8623E
7
8 Prefix: 'it8603'
9
10 Addresses scanned: from Super I/O config space (8 I/O ports)
11
12 Datasheet: Not publicly available
13
14 * IT8620E
15
16 Prefix: 'it8620'
17
18 Addresses scanned: from Super I/O config space (8 I/O ports)
19
20 * IT8628E
21
22 Prefix: 'it8628'
23
24 Addresses scanned: from Super I/O config space (8 I/O ports)
25
26 Datasheet: Not publicly available
27
28 * IT8705F
29
30 Prefix: 'it87'
31
32 Addresses scanned: from Super I/O config space (8 I/O ports)
33
34 Datasheet: Once publicly available at the ITE website, but no longer
35
36 * IT8712F
37
38 Prefix: 'it8712'
39
40 Addresses scanned: from Super I/O config space (8 I/O ports)
41
42 Datasheet: Once publicly available at the ITE website, but no longer
43
44 * IT8716F/IT8726F
45
46 Prefix: 'it8716'
47
48 Addresses scanned: from Super I/O config space (8 I/O ports)
49
50 Datasheet: Once publicly available at the ITE website, but no longer
51
52 * IT8718F
53
54 Prefix: 'it8718'
55
56 Addresses scanned: from Super I/O config space (8 I/O ports)
57
58 Datasheet: Once publicly available at the ITE website, but no longer
59
60 * IT8720F
61
62 Prefix: 'it8720'
63
64 Addresses scanned: from Super I/O config space (8 I/O ports)
65
66 Datasheet: Not publicly available
67
68 * IT8721F/IT8758E
69
70 Prefix: 'it8721'
71
72 Addresses scanned: from Super I/O config space (8 I/O ports)
73
74 Datasheet: Not publicly available
75
76 * IT8728F
77
78 Prefix: 'it8728'
79
80 Addresses scanned: from Super I/O config space (8 I/O ports)
81
82 Datasheet: Not publicly available
83
84 * IT8732F
85
86 Prefix: 'it8732'
87
88 Addresses scanned: from Super I/O config space (8 I/O ports)
89
90 Datasheet: Not publicly available
91
92 * IT8771E
93
94 Prefix: 'it8771'
95
96 Addresses scanned: from Super I/O config space (8 I/O ports)
97
98 Datasheet: Not publicly available
99
100 * IT8772E
101
102 Prefix: 'it8772'
103
104 Addresses scanned: from Super I/O config space (8 I/O ports)
105
106 Datasheet: Not publicly available
107
108 * IT8781F
109
110 Prefix: 'it8781'
111
112 Addresses scanned: from Super I/O config space (8 I/O ports)
113
114 Datasheet: Not publicly available
115
116 * IT8782F
117
118 Prefix: 'it8782'
119
120 Addresses scanned: from Super I/O config space (8 I/O ports)
121
122 Datasheet: Not publicly available
123
124 * IT8783E/F
125
126 Prefix: 'it8783'
127
128 Addresses scanned: from Super I/O config space (8 I/O ports)
129
130 Datasheet: Not publicly available
131
132 * IT8786E
133
134 Prefix: 'it8786'
135
136 Addresses scanned: from Super I/O config space (8 I/O ports)
137
138 Datasheet: Not publicly available
139
140 * IT8790E
141
142 Prefix: 'it8790'
143
144 Addresses scanned: from Super I/O config space (8 I/O ports)
145
146 Datasheet: Not publicly available
147
148 * SiS950 [clone of IT8705F]
149
150 Prefix: 'it87'
151
152 Addresses scanned: from Super I/O config space (8 I/O ports)
153
154 Datasheet: No longer be available
155
156
157Authors:
158 - Christophe Gauthron
159 - Jean Delvare <jdelvare@suse.de>
160
161
162Module Parameters
163-----------------
164
165* update_vbat: int
166 0 if vbat should report power on value, 1 if vbat should be updated after
167 each read. Default is 0. On some boards the battery voltage is provided
168 by either the battery or the onboard power supply. Only the first reading
169 at power on will be the actual battery voltage (which the chip does
170 automatically). On other boards the battery voltage is always fed to
171 the chip so can be read at any time. Excessive reading may decrease
172 battery life but no information is given in the datasheet.
173
174* fix_pwm_polarity int
175 Force PWM polarity to active high (DANGEROUS). Some chips are
176 misconfigured by BIOS - PWM values would be inverted. This option tries
177 to fix this. Please contact your BIOS manufacturer and ask him for fix.
178
179
180Hardware Interfaces
181-------------------
182
183All the chips supported by this driver are LPC Super-I/O chips, accessed
184through the LPC bus (ISA-like I/O ports). The IT8712F additionally has an
185SMBus interface to the hardware monitoring functions. This driver no
186longer supports this interface though, as it is slower and less reliable
187than the ISA access, and was only available on a small number of
188motherboard models.
189
190
191Description
192-----------
193
194This driver implements support for the IT8603E, IT8620E, IT8623E, IT8628E,
195IT8705F, IT8712F, IT8716F, IT8718F, IT8720F, IT8721F, IT8726F, IT8728F, IT8732F,
196IT8758E, IT8771E, IT8772E, IT8781F, IT8782F, IT8783E/F, IT8786E, IT8790E, and
197SiS950 chips.
198
199These chips are 'Super I/O chips', supporting floppy disks, infrared ports,
200joysticks and other miscellaneous stuff. For hardware monitoring, they
201include an 'environment controller' with 3 temperature sensors, 3 fan
202rotation speed sensors, 8 voltage sensors, associated alarms, and chassis
203intrusion detection.
204
205The IT8712F and IT8716F additionally feature VID inputs, used to report
206the Vcore voltage of the processor. The early IT8712F have 5 VID pins,
207the IT8716F and late IT8712F have 6. They are shared with other functions
208though, so the functionality may not be available on a given system.
209
210The IT8718F and IT8720F also features VID inputs (up to 8 pins) but the value
211is stored in the Super-I/O configuration space. Due to technical limitations,
212this value can currently only be read once at initialization time, so
213the driver won't notice and report changes in the VID value. The two
214upper VID bits share their pins with voltage inputs (in5 and in6) so you
215can't have both on a given board.
216
217The IT8716F, IT8718F, IT8720F, IT8721F/IT8758E and later IT8712F revisions
218have support for 2 additional fans. The additional fans are supported by the
219driver.
220
221The IT8716F, IT8718F, IT8720F, IT8721F/IT8758E, IT8732F, IT8781F, IT8782F,
222IT8783E/F, and late IT8712F and IT8705F also have optional 16-bit tachometer
223counters for fans 1 to 3. This is better (no more fan clock divider mess) but
224not compatible with the older chips and revisions. The 16-bit tachometer mode
225is enabled by the driver when one of the above chips is detected.
226
227The IT8726F is just bit enhanced IT8716F with additional hardware
228for AMD power sequencing. Therefore the chip will appear as IT8716F
229to userspace applications.
230
231The IT8728F, IT8771E, and IT8772E are considered compatible with the IT8721F,
232until a datasheet becomes available (hopefully.)
233
234The IT8603E/IT8623E is a custom design, hardware monitoring part is similar to
235IT8728F. It only supports 3 fans, 16-bit fan mode, and the full speed mode
236of the fan is not supported (value 0 of pwmX_enable).
237
238The IT8620E and IT8628E are custom designs, hardware monitoring part is similar
239to IT8728F. It only supports 16-bit fan mode. Both chips support up to 6 fans.
240
241The IT8790E supports up to 3 fans. 16-bit fan mode is always enabled.
242
243The IT8732F supports a closed-loop mode for fan control, but this is not
244currently implemented by the driver.
245
246Temperatures are measured in degrees Celsius. An alarm is triggered once
247when the Overtemperature Shutdown limit is crossed.
248
249Fan rotation speeds are reported in RPM (rotations per minute). An alarm is
250triggered if the rotation speed has dropped below a programmable limit. When
25116-bit tachometer counters aren't used, fan readings can be divided by
252a programmable divider (1, 2, 4 or 8) to give the readings more range or
253accuracy. With a divider of 2, the lowest representable value is around
2542600 RPM. Not all RPM values can accurately be represented, so some rounding
255is done.
256
257Voltage sensors (also known as IN sensors) report their values in volts. An
258alarm is triggered if the voltage has crossed a programmable minimum or
259maximum limit. Note that minimum in this case always means 'closest to
260zero'; this is important for negative voltage measurements. On most chips, all
261voltage inputs can measure voltages between 0 and 4.08 volts, with a resolution
262of 0.016 volt. IT8603E, IT8721F/IT8758E and IT8728F can measure between 0 and
2633.06 volts, with a resolution of 0.012 volt. IT8732F can measure between 0 and
2642.8 volts with a resolution of 0.0109 volt. The battery voltage in8 does not
265have limit registers.
266
267On the IT8603E, IT8620E, IT8628E, IT8721F/IT8758E, IT8732F, IT8781F, IT8782F,
268and IT8783E/F, some voltage inputs are internal and scaled inside the chip:
269* in3 (optional)
270* in7 (optional for IT8781F, IT8782F, and IT8783E/F)
271* in8 (always)
272* in9 (relevant for IT8603E only)
273The driver handles this transparently so user-space doesn't have to care.
274
275The VID lines (IT8712F/IT8716F/IT8718F/IT8720F) encode the core voltage value:
276the voltage level your processor should work with. This is hardcoded by
277the mainboard and/or processor itself. It is a value in volts.
278
279If an alarm triggers, it will remain triggered until the hardware register
280is read at least once. This means that the cause for the alarm may already
281have disappeared! Note that in the current implementation, all hardware
282registers are read whenever any data is read (unless it is less than 1.5
283seconds since the last update). This means that you can easily miss
284once-only alarms.
285
286Out-of-limit readings can also result in beeping, if the chip is properly
287wired and configured. Beeping can be enabled or disabled per sensor type
288(temperatures, voltages and fans.)
289
290The IT87xx only updates its values each 1.5 seconds; reading it more often
291will do no harm, but will return 'old' values.
292
293To change sensor N to a thermistor, 'echo 4 > tempN_type' where N is 1, 2,
294or 3. To change sensor N to a thermal diode, 'echo 3 > tempN_type'.
295Give 0 for unused sensor. Any other value is invalid. To configure this at
296startup, consult lm_sensors's /etc/sensors.conf. (4 = thermistor;
2973 = thermal diode)
298
299
300Fan speed control
301-----------------
302
303The fan speed control features are limited to manual PWM mode. Automatic
304"Smart Guardian" mode control handling is only implemented for older chips
305(see below.) However if you want to go for "manual mode" just write 1 to
306pwmN_enable.
307
308If you are only able to control the fan speed with very small PWM values,
309try lowering the PWM base frequency (pwm1_freq). Depending on the fan,
310it may give you a somewhat greater control range. The same frequency is
311used to drive all fan outputs, which is why pwm2_freq and pwm3_freq are
312read-only.
313
314
315Automatic fan speed control (old interface)
316-------------------------------------------
317
318The driver supports the old interface to automatic fan speed control
319which is implemented by IT8705F chips up to revision F and IT8712F
320chips up to revision G.
321
322This interface implements 4 temperature vs. PWM output trip points.
323The PWM output of trip point 4 is always the maximum value (fan running
324at full speed) while the PWM output of the other 3 trip points can be
325freely chosen. The temperature of all 4 trip points can be freely chosen.
326Additionally, trip point 1 has an hysteresis temperature attached, to
327prevent fast switching between fan on and off.
328
329The chip automatically computes the PWM output value based on the input
330temperature, based on this simple rule: if the temperature value is
331between trip point N and trip point N+1 then the PWM output value is
332the one of trip point N. The automatic control mode is less flexible
333than the manual control mode, but it reacts faster, is more robust and
334doesn't use CPU cycles.
335
336Trip points must be set properly before switching to automatic fan speed
337control mode. The driver will perform basic integrity checks before
338actually switching to automatic control mode.
339
340
341Temperature offset attributes
342-----------------------------
343
344The driver supports temp[1-3]_offset sysfs attributes to adjust the reported
345temperature for thermal diodes or diode-connected thermal transistors.
346If a temperature sensor is configured for thermistors, the attribute values
347are ignored. If the thermal sensor type is Intel PECI, the temperature offset
348must be programmed to the critical CPU temperature.