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hwmon: (max31790) Fix pwmX_enable attributes

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[ Upstream commit 148c847c9e5a54b99850617bf9c143af9a344f92 ]

pwmX_enable supports three possible values:

0: Fan control disabled. Duty cycle is fixed to 0%
1: Fan control enabled, pwm mode. Duty cycle is determined by
   values written into Target Duty Cycle registers.
2: Fan control enabled, rpm mode
   Duty cycle is adjusted such that fan speed matches
   the values in Target Count registers

The current code does not do this; instead, it mixes pwm control
configuration with fan speed monitoring configuration. Worse, it
reports that pwm control would be disabled (pwmX_enable==0) when
it is in fact enabled in pwm mode. Part of the problem may be that
the chip sets the "TACH input enable" bit on its own whenever the
mode bit is set to RPM mode, but that doesn't mean that "TACH input
enable" accurately reflects the pwm mode.

Fix it up and only handle pwm control with the pwmX_enable attributes.
In the documentation, clarify that disabling pwm control (pwmX_enable=0)
sets the pwm duty cycle to 0%. In the code, explain why TACH_INPUT_EN
is set together with RPM_MODE.

While at it, only update the configuration register if the configuration
has changed, and only update the cached configuration if updating the
chip configuration was successful.

Cc: Jan Kundrát <[email protected]>
Cc: Václav Kubernát <[email protected]>
Signed-off-by: Guenter Roeck <[email protected]>
Tested-by: Václav Kubernát <[email protected]>
Reviewed-by: Jan Kundrát <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Sasha Levin <[email protected]>
This commit is contained in:
Guenter Roeck 2021-05-26 08:40:18 -07:00 • committed by Greg Kroah-Hartman
commit 2e23607e65
2 changed files with 27 additions and 16 deletions
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2
Documentation/hwmon/max31790.rst
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@ -38,7 +38,7 @@ Sysfs entries
fan[1-12]_input RO fan tachometer speed in RPM
fan[1-12]_fault RO fan experienced fault
fan[1-6]_target RW desired fan speed in RPM
pwm[1-6]_enable RW regulator mode, 0=disabled, 1=manual mode, 2=rpm mode
pwm[1-6]_enable RW regulator mode, 0=disabled (duty cycle=0%), 1=manual mode, 2=rpm mode
pwm[1-6] RW read: current pwm duty cycle,
write: target pwm duty cycle (0-255)
================== === =======================================================