On Mon, Oct 15, 2018 at 3:57 PM Atish Patra [off-list ref] wrote:

quoted

quoted

+SiFive PWM controller
+
+Unlike most other PWM controllers, the SiFive PWM controller currently only
+supports one period for all channels in the PWM. This is set globally in DTS.
+The period also has significant restrictions on the values it can achieve,
+which the driver rounds to the nearest achievable frequency.

What restrictions are these? If "nearest achievable" is too far off the
target period it might be preferable to error out.

@Wes: Any comments?

When I last looked at this driver and hardware, I briefly considered
throwing up my hands and pretending that this PWM device had no period
control at all, only duty-cycle. There are several examples of PWM
controllers in linux already that behave that way.

Most of the uses of this PWM are only going to care about the
duty-cycle, not the period. So failing when the period is unachievable
seems worse to me than just completely eliminating access to period
control.

I think yes. Since fu540 is the first Linux capable RISC-V core, SiFive
Guys decided mark it as version 0.

@Wesly: Please correct me if I am wrong.

Correct.