linux-kernel - Re: [PATCH] media: st-mipid02: add a check for devm_gpiod_get

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Message-ID: <CANhBUQ0MvXYm4iLcx5gWyq=0VMmafRAJ7TsTtUuOT0YwgBcAOA@mail.gmail.com>
Date:   Thu, 17 Oct 2019 15:48:19 +0800
From:   Chuhong Yuan <hslester96@...il.com>
To:     Mickael GUENE <mickael.guene@...com>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] media: st-mipid02: add a check for devm_gpiod_get_optional

On Thu, Oct 17, 2019 at 1:43 PM Mickael GUENE <mickael.guene@...com> wrote:
>
> Hello Chuhong,
>
>  Is this check necessary ?
> since looking into code it seems to me devm_gpiod_get_optional() can only
> return NULL in case of error due to following check in devm_gpiod_get_index_optional()
>         if (IS_ERR(desc)) {
>                 if (PTR_ERR(desc) == -ENOENT)
>                         return NULL;
>         }
>  And in that case reset_gpio is not used
>

The problem may not be a null return value, but a returned error,
which is a minus value,
like -EPROBE_DEFER or -EINVAL returned by gpiod_find in gpiod_get_index.
In these cases, devm_gpiod_get_index_optional will not return null but
return the error.
Therefore, this check is necessary.

> Regards
> Mickael
>
> On 10/16/19 12:56, Chuhong Yuan wrote:
> > mipid02_probe misses a check for devm_gpiod_get_optional and may miss
> > the failure.
> > Add a check to fix the problem.
> >
> > Signed-off-by: Chuhong Yuan <hslester96@...il.com>
> > ---
> >  drivers/media/i2c/st-mipid02.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/drivers/media/i2c/st-mipid02.c b/drivers/media/i2c/st-mipid02.c
> > index 81285b8d5cfb..d38e888b0a43 100644
> > --- a/drivers/media/i2c/st-mipid02.c
> > +++ b/drivers/media/i2c/st-mipid02.c
> > @@ -971,6 +971,9 @@ static int mipid02_probe(struct i2c_client *client)
> >       bridge->reset_gpio = devm_gpiod_get_optional(dev, "reset",
> >                                                    GPIOD_OUT_HIGH);
> >
> > +     if (IS_ERR(bridge->reset_gpio))
> > +             return PTR_ERR(bridge->reset_gpio);
> > +
> >       ret = mipid02_get_regulators(bridge);
> >       if (ret) {
> >               dev_err(dev, "failed to get regulators %d", ret);
> >