linux-kernel - Re: [RCF PATCH,v2,2/2] pwm: imx: Configure output to GPIO in disabled state

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Date:   Fri, 16 Nov 2018 08:34:30 +0100
From:   Lothar Waßmann <LW@...O-electronics.de>
To:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Vokáč Michal <Michal.Vokac@...ft.com>,
        Mark Rutland <mark.rutland@....com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-pwm@...r.kernel.org" <linux-pwm@...r.kernel.org>,
        Lukasz Majewski <l.majewski@...ess.pl>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        Fabio Estevam <fabio.estevam@....com>,
        Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [RCF PATCH,v2,2/2] pwm: imx: Configure output to GPIO in
 disabled state

Uwe Kleine-König <u.kleine-koenig@...gutronix.de> wrote:

> Hello Thierry,
> 
> On Thu, Nov 15, 2018 at 04:25:45PM +0100, Thierry Reding wrote:
> > On Wed, Nov 14, 2018 at 10:51:20PM +0100, Uwe Kleine-König wrote:  
> > > On Wed, Nov 14, 2018 at 12:34:49PM +0100, Thierry Reding wrote:  
[...]
> > > Also dts writes don't need to lookup the needed GPIO numbers and pinctrl.  
> > 
> > Just to clarify: I don't think that we need to get the GPIO number
> > involved in this case, because we don't have to reconfigure the pin as
> > GPIO to make this work. The only reason that Michal's proposal did that
> > is because that was believed to be necessary. But if the pin can just be
> > configured with a 100k pull-up, that's enough to pull the pin high when
> > we need it.  
> 
> Unless the gpio happens to be configured as output at the wrong value.
> Further I'm not sure if the pwm in disabled state actively pulls to 0
> and if in this state the PU of the pin is good enough to ensure a one
> here. That would need verification first.
> 
No. You can disable the output driver via pinctrl, so that only the
selected pull-up/down is relevant. The pin function and GPIO register
settings don't matter at all in this case.


Lothar Waßmann
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