625ee7d267
[ 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 <jan.kundrat@cesnet.cz> Cc: Václav Kubernát <kubernat@cesnet.cz> Signed-off-by: Guenter Roeck <linux@roeck-us.net> Tested-by: Václav Kubernát <kubernat@cesnet.cz> Reviewed-by: Jan Kundrát <jan.kundrat@cesnet.cz> Link: https://lore.kernel.org/r/20210526154022.3223012-4-linux@roeck-us.net Signed-off-by: Sasha Levin <sashal@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.