Date:   Tue, 20 Jul 2021 10:22:40 +0300
From:   Alexandru Ardelean <ardeleanalex@...il.com>
To:     Théo Borém Fabris <theobf@....br>
Cc:     Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        linux-iio <linux-iio@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] iio: dac: max5821: convert device register to device
 managed function

On Mon, Jul 19, 2021 at 6:25 PM Théo Borém Fabris <theobf@....br> wrote:
>
> Hi, Alexandru.
>
> Em seg., 19 de jul. de 2021 às 04:33, Alexandru Ardelean
> <ardeleanalex@...il.com> escreveu:
> >
> > On Sun, Jul 18, 2021 at 11:42 PM Théo Borém Fabris <theobf@....br> wrote:
> > >
> > > Add a device managed hook, via devm_add_action_or_reset() and
> > > max5821_regulator_disable(), to disable voltage regulator on device
> > > detach.
> > > Replace iio_device_register() by devm_iio_device_register() and remove
> > > the max5821_remove() function used to unregister the device and disable the
> > > voltage regulator.
> > > Remove i2c_set_clientdata() from the probe function, since
> > > i2c_get_clientdata() is not used anymore.
> >
> > Looks good overall.
> > A few comments inline.
> >
> > >
> > > Signed-off-by: Théo Borém Fabris <theobf@....br>
> > > ---
> > >  drivers/iio/dac/max5821.c | 30 ++++++++++++++++--------------
> > >  1 file changed, 16 insertions(+), 14 deletions(-)
> > >
> > > diff --git a/drivers/iio/dac/max5821.c b/drivers/iio/dac/max5821.c
> > > index bd6e75699a63..44c04ae70b32 100644
> > > --- a/drivers/iio/dac/max5821.c
> > > +++ b/drivers/iio/dac/max5821.c
> > > @@ -294,6 +294,13 @@ static const struct iio_info max5821_info = {
> > >         .write_raw = max5821_write_raw,
> > >  };
> > >
> > > +static void max5821_regulator_disable(void *data)
> > > +{
> > > +       struct regulator *rdata = data;
> > > +
> > > +       regulator_disable(rdata);
> >
> > This can be simplified a bit:
> >
> > static void max5821_regulator_disable(void *reg)
> > {
> >       regulator_disable(reg);
> > }
> >
> > I used to do explicit casting, but then I also figured that it's not necessary.
> >
> Ok.
>
> > > +}
> > > +
> > >  static int max5821_probe(struct i2c_client *client,
> > >                         const struct i2c_device_id *id)
> > >  {
> > > @@ -306,7 +313,6 @@ static int max5821_probe(struct i2c_client *client,
> > >         if (!indio_dev)
> > >                 return -ENOMEM;
> > >         data = iio_priv(indio_dev);
> > > -       i2c_set_clientdata(client, indio_dev);
> > >         data->client = client;
> > >         mutex_init(&data->lock);
> > >
> > > @@ -331,6 +337,14 @@ static int max5821_probe(struct i2c_client *client,
> > >                 goto error_free_reg;
> > >         }
> > >
> > > +       ret = devm_add_action_or_reset(&client->dev, max5821_regulator_disable,
> > > +                                      data->vref_reg);
> > > +       if (ret) {
> > > +               dev_err(&client->dev,
> > > +                       "Failed to add action to managed regulator: %d\n", ret);
> > > +               goto error_disable_reg;
> >
> > return ret;
> >
> > devm_add_action_or_reset() should call max5821_regulator_disable() in
> > case of error
> >
> Ok.
>
> > > +       }
> > > +
> > >         ret = regulator_get_voltage(data->vref_reg);
> > >         if (ret < 0) {
> > >                 dev_err(&client->dev,
> > > @@ -346,7 +360,7 @@ static int max5821_probe(struct i2c_client *client,
> > >         indio_dev->modes = INDIO_DIRECT_MODE;
> > >         indio_dev->info = &max5821_info;
> > >
> > > -       return iio_device_register(indio_dev);
> > > +       return devm_iio_device_register(&client->dev, indio_dev);
> > >
> > >  error_disable_reg:
> >
> > This entire goto block should be removed.
> > The idea of using only devm_ functions is to not have these goto statements.
> >
> I thought the action added via devm_add_action (and devres_add) was called only
> on driver detach, thus the error_disable_reg label would be necessary
> to handle the

devm_add_action() yes
this is devm_add_action_or_reset() which looks like this:

static inline int devm_add_action_or_reset(struct device *dev,
                       void (*action)(void *), void *data)
{
    int ret;

    ret = devm_add_action(dev, action, data);
    if (ret)
        action(data);

    return ret;
}

it can be found in "include/linux/device.h"

> possible error on regulator_get_voltage. Could you please clarify for
> me when does
> a driver detach happen?

a driver detach happens when:
* the kmod is unloaded (assuming the driver is running as a kmod)
* manually unbinding the driver from sysfs ;
   a quick article about this [it's for USB, but other interfaces use
   the same mechanism]:
   https://lwn.net/Articles/143397/
   there should be something under /sys/bus/spi/drivers/xxxx/unbind
* when the system powers down (reboots)
* maybe there is some other new method to do this [that I don't know about]

>
> Thanks for your reply,
> Théo
>
> > >         regulator_disable(data->vref_reg);
> > > @@ -356,17 +370,6 @@ static int max5821_probe(struct i2c_client *client,
> > >         return ret;
> > >  }
> > >
> > > -static int max5821_remove(struct i2c_client *client)
> > > -{
> > > -       struct iio_dev *indio_dev = i2c_get_clientdata(client);
> > > -       struct max5821_data *data = iio_priv(indio_dev);
> > > -
> > > -       iio_device_unregister(indio_dev);
> > > -       regulator_disable(data->vref_reg);
> > > -
> > > -       return 0;
> > > -}
> > > -
> > >  static const struct i2c_device_id max5821_id[] = {
> > >         { "max5821", ID_MAX5821 },
> > >         { }
> > > @@ -386,7 +389,6 @@ static struct i2c_driver max5821_driver = {
> > >                 .pm     = &max5821_pm_ops,
> > >         },
> > >         .probe          = max5821_probe,
> > > -       .remove         = max5821_remove,
> > >         .id_table       = max5821_id,
> > >  };
> > >  module_i2c_driver(max5821_driver);
> > > --
> > > 2.20.1
> > >

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