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authorAndrew Jeffery <andrew@aj.id.au>2017-11-20 07:42:06 +0300
committerGuenter Roeck <linux@roeck-us.net>2018-01-03 02:05:34 +0300
commitcf583b4275761754638c946ff777546d1a9b6744 (patch)
tree1148c9ee65f4f716352c7d9d2a8b5f79611d9453 /Documentation/hwmon
parent464df6fa3766784b85b00d56cd4d7c706aee5375 (diff)
downloadlinux-cf583b4275761754638c946ff777546d1a9b6744.tar.xz
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/max317858
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