linux-kernel - Re: [PATCH v2] pwm: Introduce single-PWM of

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Date:   Mon, 26 Apr 2021 10:24:27 -0500
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Uwe Kleine-K?nig <u.kleine-koenig@...gutronix.de>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Lee Jones <lee.jones@...aro.org>, linux-pwm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] pwm: Introduce single-PWM of_xlate function

On Sat 24 Apr 06:32 CDT 2021, Uwe Kleine-K?nig wrote:

> Hello,
> 
> On Fri, Apr 23, 2021 at 04:33:04PM -0500, Bjorn Andersson wrote:
> > The existing pxa driver and the upcoming addition of PWM support in the
> > TI sn565dsi86 DSI/eDP bridge driver both has a single PWM channel and
> > thereby a need for a of_xlate function with the period as its single
> > argument.
> > 
> > Introduce a common helper function in the core that can be used as
> > of_xlate by such drivers and migrate the pxa driver to use this.
> > 
> > Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
> 
> I'm OK with the idea as such. I'd like to see the semantic expanded a
> bit however such that the function can parse
> 
> 	pwms = <&mypwm 50000>;
> 
> and also
> 
> 	pwms = <&mypwm 500000 PWM_POLARITY_INVERTED>;
> 
> . You suggetion only covers the former.

One concern though is that a single-channel pwm with the optional flag
would syntactically be indistinguishable from a multi-channel property
without flags. Presumably the values are out of range though, so I
suppose there's no problem in practice.

Please let me know if you think there's any merit to this concern and
I'll respin the patch accordingly.

Thanks,
Bjorn

> 
> See
> https://lore.kernel.org/r/20210315111124.2475274-2-u.kleine-koenig@pengutronix.de
> for my first attempt to unify of_pwm_xlate_with_flags and
> of_pwm_simple_xlate accordingly.
> 
> Best regards
> Uwe
> 
> -- 
> Pengutronix e.K.                           | Uwe Kleine-König            |
> Industrial Linux Solutions                 | https://www.pengutronix.de/ |