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

Jeff LaBundy
2020-01-10T04:29:14Z

Hi Uwe,

On Tue, Jan 07, 2020 at 12:19:40PM +0100, Uwe Kleine-König wrote:
> 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.
>

Agreed in full. We should be covered here since we report the (fixed)
period in all cases.

> Best regards
> Uwe
>
> --
> Pengutronix e.K. | Uwe Kleine-König |
> Industrial Linux Solutions | https://www.pengutronix.de/ |

I managed to send out v3 this past weekend; please let me know if you
have any further feedback or you find it to be satisfactory.

Kind regards,
Jeff LaBundy