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d206636e76
Expose fanX_target, pwmX and pwmX_enable hwmon sysfs attributes. Fans in a PMBus device are driven by the configuration of two registers, FAN_CONFIG_x_y and FAN_COMMAND_x: FAN_CONFIG_x_y dictates how the fan and the tacho operate (if installed), while FAN_COMMAND_x sets the desired fan rate. The unit of FAN_COMMAND_x is dependent on the operational fan mode, RPM or PWM percent duty, as determined by the corresponding configuration in FAN_CONFIG_x_y. The mapping of fanX_target, pwmX and pwmX_enable onto FAN_CONFIG_x_y and FAN_COMMAND_x is implemented with the addition of virtual registers to facilitate the necessary side-effects of each access: 1. PMBUS_VIRT_FAN_TARGET_x 2. PMBUS_VIRT_PWM_x 3. PMBUS_VIRT_PWM_ENABLE_x Some complexity arises with the fanX_target and pwmX attributes both mapping onto FAN_COMMAND_x: There is no general mapping between PWM percent duty and RPM, so we can't display values in either attribute in terms of the other (which in my mind is the intuitive, if impossible, behaviour). This problem also affects the pwmX_enable attribute which allows userspace to switch between full speed, manual PWM and a number of automatic control modes, possibly including a switch to RPM behaviour (e.g. automatically adjusting PWM duty to reach a RPM target, the behaviour of fanX_target). The next most intuitive behaviour is for fanX_target and pwmX to simply be independent, to retain their most recently set value even if that value is not active on the hardware (due to switching to the alternative control mode). This property of retaining the value independent of the hardware state has useful results for both userspace and the kernel: Userspace always sees a sensible value in the attribute (the last thing it was set to, as opposed to 0 or receiving an error on read), and the kernel can use the attributes as a value cache. This latter point eases the implementation of pwmX_enable, which can look up the associated pmbus_sensor object, take its cached value and apply it to hardware on changing control mode. This ensures we will not arbitrarily set a PWM value as an RPM value or vice versa, and we can assume that the RPM or PWM value set was sensible at least at some point in the past. Finally, the DIRECT mode coefficients of some controllers is different between RPM and PWM percent duty control modes, so PSC_PWM is introduced to capture the necessary coefficients. As pmbus core had no PWM support previously PSC_FAN continues to be used to capture the RPM DIRECT coefficients, but in order to avoid falsely applying RPM scaling to PWM values I have introduced the PMBUS_HAVE_PWM12 and PMB_BUS_HAVE_PWM34 feature bits. These feature bits allow drivers to explicitly declare PWM support in order to have the attributes exposed. Signed-off-by: Andrew Jeffery <andrew@aj.id.au> Signed-off-by: Guenter Roeck <linux@roeck-us.net> |
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Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.