Re: [PATCH v4 05/11] pwm: add support for sl28cpld PWM controller

On Fri, Jun 5, 2020 at 11:51 AM Lee Jones [off-list ref] wrote:

On Thu, 04 Jun 2020, Michael Walle wrote:

...

quoted

+     cycle = state->duty_cycle * config->max_duty_cycle;
+     do_div(cycle, state->period);

Forgive my ignorance (I'm new here!), but what are these 2 lines
doing?  Here we are multiplying the current duty_cycle with the
maximum value, then dividing by the period.

So in the case of PWM_MODE_1KHZ with a 50% duty cycle, you'd have:

   (500000 * 0x20[16]) / 1000000 = [0x10]16

Thus, the above gives as a proportional representation of the maximum
valid value for placement into the cycle control register(s), right?

Either way (whether I'm correct or not), I think it would be nice to
mention this in a comment.  Maybe even clarify with a simple example.

IIRC PWM has a helper for that (to calc period based on PWM state and
new duty cycle %).

-- 
With Best Regards,
Andy Shevchenko

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel