Hi Miquèl, On Mon, Jan 20, 2020 at 04:38:22PM +0100, Miquel Raynal wrote: > One dumb question that I still have is: besides any backward > compatibility aspects, do we really care about the period/frequency of > the PWM? Why do we enforce a period and an active duration, while > we could limit ourselves to a ratio and let the driver use the most > suitable frequency if the hardware supports it? There are situations where just fixing the ratio would (nearly) be good enough. For example if you drive an LED just requesting a ratio might look fine at first glance. But .period = 5000 ms, .duty_cycle = 2500 ms has quite a different effect than .period = 500 ns, .duty_cycle = 250 ns while both are valid if you requested 50%. Having said that I think the lowlevel API (i.e. what a device driver has to implement) is sane, as it allows to implement all possible requests, even if there might be a consumer that cares more about the absolute value of duty-cycle than the duty-cycle/period ratio; and it matches what most hardware models implement. There is usually a register to specify the period and one to specify the duty-cycle. And on top of that (at least once there is pwm_round_state()) you can implement all sort of helper functions that implement for example "best effort 50% with a period < 2ms". Best regards Uwe -- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | https://www.pengutronix.de/ |