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

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Message-ID: <20181122190321.ktqegs7kpvhcemvi@pengutronix.de>
Date:   Thu, 22 Nov 2018 20:03:21 +0100
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Vokáč Michal <Michal.Vokac@...ft.com>
Cc:     Lothar Waßmann <LW@...O-electronics.de>,
        Thierry Reding <thierry.reding@...il.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>,
        viresh kumar <viresh.kumar@...aro.org>
Subject: Re: [RCF PATCH,v2,2/2] pwm: imx: Configure output to GPIO in
 disabled state

Hello Michal,

On Thu, Nov 22, 2018 at 04:46:39PM +0000, Vokáč Michal wrote:
> On 22.11.2018 17:23, Uwe Kleine-König wrote:
> > On Thu, Nov 22, 2018 at 03:42:14PM +0000, Vokáč Michal wrote:
> >> On 16.11.2018 09:25, Uwe Kleine-König wrote:
> >>> On Fri, Nov 16, 2018 at 08:34:30AM +0100, Lothar Waßmann wrote:
> >>>> 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, please can you be more specific how would you do that? IFAIK the
> >> pull-up/down internal resistors have effect only if the pin is configured
> >> as GPIO *input* (on i.MX6 at least). See the TRM, 29.4.2.2 Output driver:
> >>
> >>    "Internal pull-up, pull-down resistors, and pad keeper are disabled in
> >>     output mode."

This would mean you'd have to rely on an external pull up for your use
case. I wouldn't be surprised however if DSE=0 wouldn't count as "output
mode". Given the reliability of NXP documentation I wouldn't bet neither
on one nor the other possibility.

> > So I'd expect this to really work on i.MX6 but not the earlier SoCs
> > without a gpio specifier.
> 
> Maybe you would expect it to work but I already tested and measured
> that weeks ago ;) It did not work.

Which pin/gpio do we talk about? Which i.MX6 variant did you test this
on? (Assuming i.MX6D or i.MX6Q and PAD_DISP0_DATA09, did you try setting

	IOMUXC_SW_MUX_CTL_PAD_DISP0_DATA09 (0x020E0194) = 0x00000005
	IOMUXC_SW_PAD_CTL_PAD_DISP0_DATA09 (0x020E04A8) = 0x0000b080

and then play with GPIO 4.30 direction and output value?)

Best regards
Uwe

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