Re: [PATCH v3 5/5] pwm: airoha: Add support for EN7581 SoC

[Benjamin Larsson <benjamin.larsson@genexis.eu>]

On 2024-09-05 11:30, Uwe Kleine-König wrote:
> 1 second long pulses with a period size of 1 second, so a constant high
> signal?

Hi, I think I was unclear. The SoC documentation is not that detailed. 
But I think I understand how it works now.

One register contains the minimum duration (d_min). And then there is 
one 8 bit register for the signal low period (lp) and then another 8bit 
register for the high period (hp). Per my understanding a change of 
polarity is then just a swap of lp and hp.

The period is d_min * (lp + hp) and duty_cycle (on time) is then 
d_min*hp (per my understanding of the linux api). This means that there 
can be different settings that result in the same pwm signal (if you 
double d_min and halving lp and hp the signal should be the same).

This means that when requesting a period and duty cycle you need to 
search through the configuration space to find the optimal value.

>
> Another thing that would be interesting is, if it can happen that you
> get a mixed signal. That is, if you update from
>
> 	.period = A
> 	.duty_cycle = B
>
> to
>
> 	.period = C
> 	.duty_cycle = D
>
> that you get one period with length C and duty_cycle B when the period
> completes after configuring period but before duty_cycle.
>
> Best regards
> UWe

I will perform this test also.

MvH

Benjamin Larsson