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. This failure to assign a value is unrelated to having multiple PWMs, I think I may have horribly worded my statement when I originally replied to you with: > 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. "reporting here" from that quote being the period/duty cycle calculations in the drivers get_state(). By "the checks" I meant making sure that a period where posedge = negedge is not set by the driver. I think I also may have mistakenly assumed the -EINVAL came from my code and not from the core - but I cannot be sure as it has been a few weeks. The check in the core looks to be things "working as intended", and it looks like I am working around it here. Should I just note what the values are on reset in the "limitations" comment and the top & it is up to applications that control the PWMs to first "fix" the duty cycle before changing the period? Hopefully I've done a better job at explaning this time, Conor.
