diff options
| author | Andrew Jeffery <andrew@aj.id.au> | 2017-11-20 05:42:06 +0100 |
|---|---|---|
| committer | Guenter Roeck <linux@roeck-us.net> | 2018-01-03 00:05:34 +0100 |
| commit | cf583b4275761754638c946ff777546d1a9b6744 (patch) | |
| tree | 1148c9ee65f4f716352c7d9d2a8b5f79611d9453 /Documentation/hwmon | |
| parent | hwmon: (pmbus) Add virtual page config bit (diff) | |
| download | linux-cf583b4275761754638c946ff777546d1a9b6744.tar.xz linux-cf583b4275761754638c946ff777546d1a9b6744.zip | |
hwmon: (pmbus/max31785) Add dual tachometer support
The dual tachometer feature is implemented in hardware with a TACHSEL
input to indicate the rotor under measurement, and exposed on the device
by extending the READ_FAN_SPEED_1 word with two extra bytes*. The need
to read the non-standard four-byte response leads to a cut-down
implementation of i2c_smbus_xfer_emulated() included in the driver.
Further, to expose the second rotor tachometer value to userspace the
values are exposed through virtual pages. We re-route accesses to
FAN_CONFIG_1_2 and READ_FAN_SPEED_1 on pages 23-28 (not defined by the
hardware) to the same registers on pages 0-5, and with the latter command
we extract the value from the second word of the four-byte response.
* The documentation recommends the slower rotor be associated with
TACHSEL=0, which corresponds to the first word of the response. The
TACHSEL=0 measurement is used by the controller's closed-loop fan
management to judge target fan rate.
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Diffstat (limited to 'Documentation/hwmon')
| -rw-r--r-- | Documentation/hwmon/max31785 | 8 |
1 files changed, 5 insertions, 3 deletions
diff --git a/Documentation/hwmon/max31785 b/Documentation/hwmon/max31785 index 7b0a0a8cdb6b..270c5f865261 100644 --- a/Documentation/hwmon/max31785 +++ b/Documentation/hwmon/max31785 @@ -17,8 +17,9 @@ management with temperature and remote voltage sensing. Various fan control features are provided, including PWM frequency control, temperature hysteresis, dual tachometer measurements, and fan health monitoring. -For dual rotor fan configuration, the MAX31785 exposes the slowest rotor of the -two in the fan[1-4]_input attributes. +For dual-rotor configurations the MAX31785A exposes the second rotor tachometer +readings in attributes fan[5-8]_input. By contrast the MAX31785 only exposes +the slowest rotor measurement, and does so in the fan[1-4]_input attributes. Usage Notes ----------- @@ -31,7 +32,8 @@ Sysfs attributes fan[1-4]_alarm Fan alarm. fan[1-4]_fault Fan fault. -fan[1-4]_input Fan RPM. +fan[1-8]_input Fan RPM. On the MAX31785A, inputs 5-8 correspond to the + second rotor of fans 1-4 fan[1-4]_target Fan input target in[1-6]_crit Critical maximum output voltage |