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

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Message-ID: <20181126115123.GA15164@ulmo>
Date:   Mon, 26 Nov 2018 12:51:23 +0100
From:   Thierry Reding <thierry.reding@...il.com>
To:     Vokáč Michal <Michal.Vokac@...ft.com>
Cc:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Lothar Waßmann <LW@...o-electronics.de>,
        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

On Fri, Nov 23, 2018 at 03:15:11PM +0000, Vokáč Michal wrote:
> On 22.11.2018 20:03, Uwe Kleine-König wrote:
> > 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.
> 
> Yeah, the NXP documentation sometimes does not really match reality.
> My use case is based on the fact that I configure the pin as input in
> the driver. Then it works just fine.
> 
> >>> 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?)
> 
> My test setup is as follows:
> - SoC is i.MX6DL or i.MX6S - I have three board variants in total.
> - Pin used for PWM/GPIO is PAD_GPIO9.
> - The pin is not connected to any circuit. Just a test point.
> - pinctrl setup in DT:
>    - for "pwm":
>      - fsl,pins = <MX6QDL_PAD_GPIO_9__PWM1_OUT 0x8>
>      - IOMUXC_SW_MUX_CTL_PAD_GPIO09 = 0x00000004
>      - IOMUXC_SW_PAD_CTL_PAD_GPIO09 = 0x00000008
> 
>    - for "gpio":
>     - fsl,pins = <MX6QDL_PAD_GPIO_9__GPIO1_IO09 0xb000>
>     - IOMUXC_SW_MUX_CTL_PAD_GPIO09 = 0x00000005
>     - IOMUXC_SW_PAD_CTL_PAD_GPIO09 = 0x0000b000

Does it help if you additionally set the ODE bit (bit 11) here?

Thierry

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