linux-kernel - Re: [RFC PATCH] i2c: core: dont change pinmux state to GPIO during recovery setup

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Message-ID: <CA+HBbNG9uXEhYjaKR6ixhN1uESmypgjqmCTayvWknUt03BYQNg@mail.gmail.com>
Date:   Wed, 13 Sep 2023 20:49:25 +0200
From:   Robert Marko <robert.marko@...tura.hr>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     wsa@...nel.org, codrin.ciubotariu@...rochip.com,
        linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
        luka.perkov@...tura.hr
Subject: Re: [RFC PATCH] i2c: core: dont change pinmux state to GPIO during
 recovery setup

On Wed, Sep 6, 2023 at 6:55 PM Russell King (Oracle)
<linux@...linux.org.uk> wrote:
>
> On Wed, Sep 06, 2023 at 04:41:33PM +0200, Robert Marko wrote:
> > On Fri, Sep 1, 2023 at 1:49 PM Robert Marko <robert.marko@...tura.hr> wrote:
> > >
> > > Ever since PXA I2C driver was moved to the generic I2C recovery, I2C has
> > > stopped working completely on Armada 3720 if the pins are specified in DTS.
> > >
> > > After a while it was traced down to the only difference being that PXA
> > > driver did not change the pinmux state to GPIO before trying to acquire the
> > > GPIO pins.
> > > And indeed as soon as this call is removed I2C starts working.
> > >
> > > To me it seems that this call is not required at all as devm_gpiod_get()
> > > will result in the pinmux state being changed to GPIO via the pinmux
> > > set_mux() op.
> > >
> > > Fixes: 0b01392c18b9 ("i2c: pxa: move to generic GPIO recovery")
> > > Signed-off-by: Robert Marko <robert.marko@...tura.hr>
> > > ---
> > > I am aware this probably isnt the correct fix, so I am sending it as RFC
> > > cause I have ran out of ideas.
> >
> > CC-ing Russel as well since I forgot him.
>
> So the generic recovery decided to set the pinmux state before calling
> devm_gpiod_get(), where as the driver (and my code) originally did this
> after calling devm_gpiod_get():
>
> -       /*
> -        * Claiming GPIOs can change the pinmux state, which confuses the
> -        * pinctrl since pinctrl's idea of the current setting is unaffected
> -        * by the pinmux change caused by claiming the GPIO. Work around that
> -        * by switching pinctrl to the GPIO state here. We do it this way to
> -        * avoid glitching the I2C bus.
> -        */
> -       pinctrl_select_state(i2c->pinctrl, i2c->pinctrl_recovery);
> -
> -       return pinctrl_select_state(i2c->pinctrl, i2c->pinctrl_default);
>
> I'd suggest re-implementing my original scheme in the generic code
> because this _does_ work on Armada 3720 hardware.
>
> Removing the pinmux frobbing is likely to break stuff.

Hi Russel,
Sorry for the late reply, its been a busy week.

I have tried doing exactly that and calling:

if (bri->pinctrl)
pinctrl_select_state(bri->pinctrl, bri->pins_gpio);
/* change the state of the pins back to their default state */
if (bri->pinctrl)
pinctrl_select_state(bri->pinctrl, bri->pins_default);

However doing that in the generic code does not work, only thing that has
worked so far is removing the GPIO pinctrl call completely.

Regards,
Robert
>
> --
> RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
> FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last!



-- 
Robert Marko
Staff Embedded Linux Engineer
Sartura Ltd.
Lendavska ulica 16a
10000 Zagreb, Croatia
Email: robert.marko@...tura.hr
Web: www.sartura.hr