Re: [PATCH v10 3/4] pwm: add microchip soft ip corePWM driver

Conor Dooley
2022-09-30T13:49:55Z

On Fri, Sep 30, 2022 at 03:39:33PM +0200, Uwe Kleine-König wrote:
> On Fri, Sep 30, 2022 at 10:45:56AM +0100, Conor Dooley wrote:
> > On Fri, Sep 30, 2022 at 11:13:16AM +0200, Uwe Kleine-König wrote:
> > > On Mon, Sep 19, 2022 at 03:29:19PM +0100, Conor Dooley wrote:
> > > > Hey Uwe,
> > > >
> > > > On Mon, Sep 19, 2022 at 03:50:08PM +0200, Uwe Kleine-König wrote:
> > > > > On Mon, Sep 19, 2022 at 01:53:56PM +0100, Conor Dooley wrote:
> > > > > > Because I was running into conflicts between the reporting here and some
> > > > > > of the checks that I have added to prevent the PWM being put into an
> > > > > > invalid state. On boot both negedge and posedge will be zero & this was
> > > > > > preventing me from setting the period at all.
> > > > >
> > > > > I don't understood that.
> > > >
> > > > On startup, (negedge == posedge) is true as both are zero, but the reset
> > > > values for prescale and period are actually 0x8. If on reset I try to
> > > > set a small period, say "echo 1000 > period" apply() returns -EINVAL
> > > > because of a check in the pwm core in pwm_apply_state() as I am
> > > > attempting to set the period to lower than the out-of-reset duty cycle.
> > >
> > > You're supposed to keep the period for pwm#1 untouched while configuring
> > > pwm#0 only if pwm#1 already has a consumer. So if pwm#1 isn't requested,
> > > you can change the period for pwm#0.
> >
> > I must have done a bad job of explaining here, as I don't think this is
> > an answer to my question.
> >
> > On reset, the prescale and period_steps registers are set to 0x8. If I
> > attempt to set the period to do "echo 1000 > period", I get -EINVAL back
> > from pwm_apply_state() (in next-20220928 it's @ L562 in pwm/core.c) as
> > the duty cycle is computed as twice the period as, on reset, we have
> > posedge = negedge = 0x0. The check of state->duty_cycle > state->period
> > fails in pwm_apply_state() as a result.
>
> So set duty_cycle to 0 first?
>
> A problem of the sysfs interface is that you can only set one parameter
> after the other. So there you have to find a sequence of valid
> pwm_states that only differ in a single parameter between the initial
> and the desired state.
>
> That's nothing a "normal" pwm consumer would be affected by. (IMHO we
> should have a userspace API that benefits from the properties of
> pwm_apply().)

Right, so I guess I will drop the check so. That's good to know, thanks.

Would you rather I waited until after the mw to send v11?

Thanks,
Conor.