Am Mi, 15. Mär 2023 um 19:26:26 -07:00:00 schrieb Guenter Roeck
<linux@xxxxxxxxxxxx>:
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@xxxxxxxx/
for the PWM-side patch.
Regards,
Lorenz
