linux-kernel - Re: [PATCH v7 5/8] pwm: core: Support new PWM_STAGGERING

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Message-ID: <20210408173637.w26njwystfuyrgan@pengutronix.de>
Date:   Thu, 8 Apr 2021 19:36:37 +0200
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Clemens Gruber <clemens.gruber@...ruber.com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        linux-pwm@...r.kernel.org, Sven Van Asbroeck <TheSven73@...il.com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 5/8] pwm: core: Support new PWM_STAGGERING_ALLOWED flag

On Thu, Apr 08, 2021 at 05:51:36PM +0200, Clemens Gruber wrote:
> On Thu, Apr 08, 2021 at 02:50:40PM +0200, Thierry Reding wrote:
> > Yes, I think that's basically what this is saying. I think we're perhaps
> > getting hung up on the terminology here. PWM_STAGGERING_ALLOWED gives
> > the impression that we're dealing with some provider-specific feature,
> > whereas what we really want to express is that the PWM doesn't care
> > exactly when the active cycle starts and based on that a provider that
> > can support it may optimize the EMI behavior.
> > 
> > Maybe we can find a better name for this? Ultimately what this means is
> > that the consumer is primarily interested in the power output of the PWM
> > rather than the exact shape of the signal. So perhaps something like
> > PWM_USAGE_POWER would be more appropriate.
> 
> Yes, although it would then no longer be obvious that this feature leads
> to improved EMI behavior, as long as we mention that in the docs, I
> think it's a good idea
> 
> Maybe document it as follows?
> PWM_USAGE_POWER - Allow the driver to delay the start of the cycle
> for EMI improvements, as long as the power output stays the same

I don't like both names, because for someone who is only halfway into
PWM stuff it is not understandable. Maybe ALLOW_PHASE_SHIFT?
When a consumer is only interested in the power output than

	.period = 20
	.duty_cycle = 5

would also be an allowed response for the request

	.period = 200
	.duty_cycle = 50

and this is not what is in the focus here.

Best regards
Uwe

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

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