Re: [PATCH v2 4/7] pwm: Add support for Azoteq IQS620A PWM generator

Uwe Kleine-König
2020-01-07T11:19:51Z

Hi Jeff,

On Wed, Jan 01, 2020 at 10:39:36PM +0000, Jeff LaBundy wrote:
> On Sun, Dec 22, 2019 at 10:48:51PM +0100, Uwe Kleine-König wrote:
> > On Sat, Dec 21, 2019 at 03:28:01AM +0000, Jeff LaBundy wrote:
> > > Based on your other feedback, I'm moving forward under the impression that
> > > you'll still accept option (2); please let me know if I have misunderstood
> > > (thank you for being flexible).
> >
> > Yeah, that's fine. If in the end it shows that this is a bad idea we can
> > still change to (3).
>
> Sounds great. As soon as 5.5-rc5 lands this weekend, I'll rebase v3 and
> send it out.
>
> I failed to catch this in my previous reply, but the comment I've added
> to iqs620_pwm_get_state actually reads as follows:
>
> /*
> * Since the device cannot generate a 0% duty cycle, requests to do so
> * force subsequent calls to iqs620_pwm_get_state to report the output
> * as disabled with duty cycle equal to that which was in use prior to
> * the request. This is not ideal, but is the best compromise based on
> * the capabilities of the device.
> */
>
> This matches the present implementation, not your proposed comment that
> claims duty cycle is clamped to 1 / 256 ms following a request for a 0%
> duty cycle.

Yeah, if that's the mechanism that is actually implemented, that's fine
of course.

> This seems OK since the concept of a duty cycle or period aren't really
> relevant if the output is disabled in my opinion. However if you prefer
> I update iqs620_pwm_apply to clamp duty cycle to 1 / 256 ms (instead of
> leaving it untouched) in this case, please let me know.

For a disabled PWM the duty_cycle and period are not relevant, for an
enabled PWM running with 0% the period matters (at least in theory)
however.

Best regards
Uwe

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