lkml.org 
[lkml]   [2023]   [Mar]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] hwmon: pwm-fan: set usage_power on PWM state
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


\
 
 \ /
  Last update: 2023-03-27 01:05    [W:0.061 / U:0.232 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site