linux-kernel - Re: [PATCH 2/3] ASoC: codec: wcd938x: Convert to GPIO descriptors

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Message-ID: <CACRpkdZ_f2EHjTJtkOdAmdAOUsh2Xi0hsToCWuTGkoh1aCZwtA@mail.gmail.com>
Date: Mon, 24 Mar 2025 10:57:53 +0100
From: Linus Walleij <linus.walleij@...aro.org>
To: Peng Fan <peng.fan@....com>
Cc: Johan Hovold <johan@...nel.org>, Steev Klimaszewski <steev@...i.org>, 
	"Peng Fan (OSS)" <peng.fan@....nxp.com>, Liam Girdwood <lgirdwood@...il.com>, 
	Mark Brown <broonie@...nel.org>, Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>, 
	Bartosz Golaszewski <brgl@...ev.pl>, Srinivas Kandagatla <srinivas.kandagatla@...aro.org>, 
	"linux-sound@...r.kernel.org" <linux-sound@...r.kernel.org>, 
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, 
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>, 
	"linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>
Subject: Re: [PATCH 2/3] ASoC: codec: wcd938x: Convert to GPIO descriptors

On Mon, Mar 24, 2025 at 9:34 AM Peng Fan <peng.fan@....com> wrote:

> > Subject: Re: [PATCH 2/3] ASoC: codec: wcd938x: Convert to GPIO
> > descriptors
> >
> > On Mon, Mar 24, 2025 at 9:09 AM Peng Fan <peng.fan@....com>
> > wrote:
> >
> > > ok, then the only suspecting point is
> > > wcd938x->reset_gpio = devm_gpiod_get(dev, "reset", GPIOD_ASIS);
> > >
> > > I may need to use GPIOD_OUT_LOW to configure it to output as set
> > raw
> > > set value as 1.
> >
> > I think there may be a bug in gpiod_configure_flags() in gpiolib.c:
> >
> >         /* Process flags */
> >         if (dflags & GPIOD_FLAGS_BIT_DIR_OUT)
> >                 ret = gpiod_direction_output_nonotify(desc,
> >                                 !!(dflags & GPIOD_FLAGS_BIT_DIR_VAL));
> >         else
> >                 ret = gpiod_direction_input_nonotify(desc);
> >
> > Shouldn't this be:
> >
> >         if (dflags & GPIOD_FLAGS_BIT_DIR_OUT)
> >                 ret = gpiod_direction_output_nonotify(desc,
> >                                 !!(dflags & GPIOD_FLAGS_BIT_DIR_VAL));
> >         else if (dflags & GPIOD_FLAGS_BIT_DIR_SET)
> >                 ret = gpiod_direction_input_nonotify(desc);
>
> Using GPIO_ASIS should not change direction.
> This change makes sense.

Actually when looking closer at it I was wrong.

>From <linux/gpio/consumer.h>:

enum gpiod_flags {
    GPIOD_ASIS    = 0,
    GPIOD_IN    = GPIOD_FLAGS_BIT_DIR_SET,
    GPIOD_OUT_LOW    = GPIOD_FLAGS_BIT_DIR_SET | GPIOD_FLAGS_BIT_DIR_OUT,
    GPIOD_OUT_HIGH    = GPIOD_FLAGS_BIT_DIR_SET | GPIOD_FLAGS_BIT_DIR_OUT |
              GPIOD_FLAGS_BIT_DIR_VAL,
    GPIOD_OUT_LOW_OPEN_DRAIN = GPIOD_OUT_LOW | GPIOD_FLAGS_BIT_OPEN_DRAIN,
    GPIOD_OUT_HIGH_OPEN_DRAIN = GPIOD_OUT_HIGH | GPIOD_FLAGS_BIT_OPEN_DRAIN,
};

So GPIOD_ASIS does not set GPIOD_FLAGS_BIT_DIR_SET.

Then gpiod_configure_flags() has:

    /* No particular flag request, return here... */
    if (!(dflags & GPIOD_FLAGS_BIT_DIR_SET)) {
        gpiod_dbg(desc, "no flags found for GPIO %s\n", name);
        return 0;
    }

    /* Process flags */
    if (dflags & GPIOD_FLAGS_BIT_DIR_OUT)
        ret = gpiod_direction_output_nonotify(desc,
                !!(dflags & GPIOD_FLAGS_BIT_DIR_VAL));
    else
        ret = gpiod_direction_input_nonotify(desc);

So the function bails out right above (you could check the debug
print there if in doubt.)

So the behaviour is correct.

So now I have no idea what is going on again :/

But I would suggest trying to set GPIOD_OUT_LOW when requesting
the line and just check if that solves Steev:s problem
(trial-and-error).

Yours,
Linus Walleij