Hello Guenter, On Wed, Feb 11, 2026 at 10:28:55AM +0100, Richard Weinberger wrote: > The backlight of a board I am working with is controlled via PWM. > Naturally, I thought this would be a straightforward task using the > pwm-backlight driver. > > However, the PWM in question is implemented using an NCT6106D chip. > The associated HWMON driver, nct6775-core.c, does not implement a > standard PWM device interface but rather its own custom one.
Looking around in drivers/hwmon made me a sad. There are four drivers
that handle parsing #pwm-cells:
$ git grep pwm-cell drivers/hwmon/
drivers/hwmon/adt7475.c: ret =
fwnode_property_get_reference_args(fwnode, "pwms", "#pwm-cells", 0, 0, &rargs);
drivers/hwmon/amc6821.c: if (of_parse_phandle_with_args(fan_np,
"pwms", "#pwm-cells", 0, &args))
drivers/hwmon/emc2305.c: ret = of_parse_phandle_with_args(child,
"pwms", "#pwm-cells", 0, &args);
drivers/hwmon/nct7363.c: ret = of_parse_phandle_with_args(child,
"pwms", "#pwm-cells",
instead of using the pwm subsystem. Also the driver mentioned by Richard
above has some self-made PWM handling including a set of driver specific
sysfs files to control the PWMs. I stopped looking at the output of
git grep pwm drivers/hwmon/
after finding some more sad things. (My "favourite" so far was:
dev_dbg(dev, "chmod -w pwm%d failed\n", nr + 1);
.)
> I am a bit puzzled, is there a specific reason why HWMON does not
> utilize the standard PWM framework in this case?
Yes please!
I think that the PWM waveform API that exists since v6.13-rc1 is
flexible enough that hwmon chips should be able to both implement and
use it properly.
Can you please make sure that the next hardware driver for a pwm capable
chip uses a proper PWM chip? Feel free to send patch authors in my
direction for that.
And if I'm wrong and using the pwm subsystem in these cases is a burden,
I want to hear about that and discuss how this can be made better.
Thanks
Uwe
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