Messages in this thread | | | Date | Fri, 17 Mar 2023 12:33:57 +0100 | From | Lorenz Brun <> | Subject | Re: [PATCH] hwmon: pwm-fan: set usage_power on PWM state |
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Am Mi, 15. Mär 2023 um 19:26:26 -07:00:00 schrieb Guenter Roeck <linux@roeck-us.net>: > This doesn't seem to be used anywhere else. I do not understand the > rationale, and I do not understand the practical impact of this > change. > This needs to be confirmed by someone who understands what the flag is > supposed to be used for, its impact, and if it is indeed appropriate > in this context. > > Also, since in practice there is no such "less flexible hardware" > in the upstream kernel, please describe the use case in more detail. > The only pwm driver that supports usage_power is pwm-pca9685, > and that driver uses the flag for EMI reasons, not because it is > "less flexible hardware". I am not inclined to accept such a change > without specific use case or need.
The reason for this is that I have a PWM-driven fan on a Mediatek MT7986a whose PWM signal is inverted by a MOSFET. The PWM peripheral of the MT7986a however doesn't support inverted output, at least not in a strict sense (i.e. if inverted mathematically it is out of phase). The maintainer of the PWM subsystem recommended that I only mathematically invert if usage_power is set as this means that phase doesn't matter.
See https://lore.kernel.org/linux-pwm/20230309010410.2106525-1-lorenz@brun.one/ for the PWM-side patch.
Regards, Lorenz
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