linux-kernel - Re: [RFC PATCH 0/3] pwm: add support for duty

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Date: Fri, 5 Apr 2024 17:14:41 +0200
From: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To: Trevor Gamblin <tgamblin@...libre.com>
Cc: linux-pwm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	michael.hennerich@...log.com, nuno.sa@...log.com, dlechner@...libre.com
Subject: Re: [RFC PATCH 0/3] pwm: add support for duty_offset

Hello Trevor,

On Fri, Apr 05, 2024 at 10:19:20AM -0400, Trevor Gamblin wrote:
> On 2024-04-05 08:23, Uwe Kleine-König wrote:
> > Having said that I don't like the addition of .supports_offset to
> > struct pwm_chip, which only signals a new incomplete evolution of the
> > pwm framework. Better adapt all drivers and then assume all of them
> > support it.
> Can you clarify what you mean here - is the intent to put basic handling of
> duty_offset (even if that means simply setting it to 0) in each driver?

Well, it's a bit more complicated than setting it to 0. It involves
translating a setting with inverted polarity to one using .duty_offset
and make all drivers implement that accordingly.

For drivers that support both polarities the logic in .apply should be:

	if (.duty_offset >= .period - .duty_cycle)
		... set inverted polarity
	else
		... set normal polarity

I'm usure how to do the transformation in reviewable chunks. Maybe the
easiest option is a new .apply callback that honors .duty_offset?

Best regards
Uwe

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

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