linux-kernel - Re: [PATCH] iio: light: adjd_s311: convert to device-managed functions

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Date:   Mon, 5 Jul 2021 09:38:21 +0300
From:   Alexandru Ardelean <aardelean@...iqon.com>
To:     Jonathan Cameron <jic23@...nel.org>
Cc:     linux-iio <linux-iio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        pmeerw@...erw.net
Subject: Re: [PATCH] iio: light: adjd_s311: convert to device-managed functions

On Sat, 3 Jul 2021 at 20:47, Jonathan Cameron <jic23@...nel.org> wrote:
>
> On Mon, 28 Jun 2021 16:51:32 +0300
> Alexandru Ardelean <aardelean@...iqon.com> wrote:
>
> > This one is a little easier to convert to device-managed, now with the
> > devm_krealloc() function.
> >
> > The other iio_triggered_buffer_setup() and iio_device_register() can be
> > converted to their devm_ variants. And devm_krealloc() can be used to
> > (re)alloc the buffer. When the driver unloads, this will also be free'd.
> >
> > Signed-off-by: Alexandru Ardelean <aardelean@...iqon.com>
> > ---
> >  drivers/iio/light/adjd_s311.c | 34 +++++-----------------------------
> >  1 file changed, 5 insertions(+), 29 deletions(-)
> >
> > diff --git a/drivers/iio/light/adjd_s311.c b/drivers/iio/light/adjd_s311.c
> > index 17dac8d0e11d..19d60d6986a1 100644
> > --- a/drivers/iio/light/adjd_s311.c
> > +++ b/drivers/iio/light/adjd_s311.c
> > @@ -230,8 +230,8 @@ static int adjd_s311_update_scan_mode(struct iio_dev *indio_dev,
> >  {
> >       struct adjd_s311_data *data = iio_priv(indio_dev);
> >
> > -     kfree(data->buffer);
> > -     data->buffer = kmalloc(indio_dev->scan_bytes, GFP_KERNEL);
> > +     data->buffer = devm_krealloc(indio_dev->dev.parent, data->buffer,
> > +                                  indio_dev->scan_bytes, GFP_KERNEL);
> I got some complaints about exactly this trick in a review recently so I'll
> pass them on.
>
> Whilst devm_krealloc() usage like this won't lose the original reference, its
> not what people expect from a realloc() case, so to not confuse people it is
> better to do a dance where you use a local variable, then only set data->buffer
> to it once we know the realloc succeeded.
>
> That avoids this looking like the anti-pattern it would be if that were a normal
> realloc in which case you would just have leaked the original allocation.
>
> More interestingly, why are we bothering with resizing the buffer dependent on what
> is enabled?  Can't we just allocate a 128 byte buffer and not bother changing it
> as we really aren't wasting that much space?  Just embed it in the adjd_s311_data
> structure directly and don't worry about the allocations.  Will need to be
> aligned(8) though to avoid the push_to_buffer_with_timestamp() issue.
> Using something like
>
> struct {
>         s16 chans[4];
>         s64 ts __aligned(8); /* I hate x86 32 bit */

do you want to me t also add this comment? :p
[just kidding]

> } scan;
>
> Inside the priv structure should work nicely.

i agree; will do it like this;
i hesitated a bit due to the inertia of converting things to devm_

>
>
> >       if (data->buffer == NULL)
> >               return -ENOMEM;
> >
> > @@ -256,7 +256,6 @@ static int adjd_s311_probe(struct i2c_client *client,
> >               return -ENOMEM;
> >
> >       data = iio_priv(indio_dev);
> > -     i2c_set_clientdata(client, indio_dev);
> >       data->client = client;
> >
> >       indio_dev->info = &adjd_s311_info;
> > @@ -265,34 +264,12 @@ static int adjd_s311_probe(struct i2c_client *client,
> >       indio_dev->num_channels = ARRAY_SIZE(adjd_s311_channels);
> >       indio_dev->modes = INDIO_DIRECT_MODE;
> >
> > -     err = iio_triggered_buffer_setup(indio_dev, NULL,
> > -             adjd_s311_trigger_handler, NULL);
> > +     err = devm_iio_triggered_buffer_setup(&client->dev, indio_dev, NULL,
> > +                                           adjd_s311_trigger_handler, NULL);
> >       if (err < 0)
> >               return err;
> >
> > -     err = iio_device_register(indio_dev);
> > -     if (err)
> > -             goto exit_unreg_buffer;
> > -
> > -     dev_info(&client->dev, "ADJD-S311 color sensor registered\n");
> > -
> > -     return 0;
> > -
> > -exit_unreg_buffer:
> > -     iio_triggered_buffer_cleanup(indio_dev);
> > -     return err;
> > -}
> > -
> > -static int adjd_s311_remove(struct i2c_client *client)
> > -{
> > -     struct iio_dev *indio_dev = i2c_get_clientdata(client);
> > -     struct adjd_s311_data *data = iio_priv(indio_dev);
> > -
> > -     iio_device_unregister(indio_dev);
> > -     iio_triggered_buffer_cleanup(indio_dev);
> > -     kfree(data->buffer);
> > -
> > -     return 0;
> > +     return devm_iio_device_register(&client->dev, indio_dev);
> >  }
> >
> >  static const struct i2c_device_id adjd_s311_id[] = {
> > @@ -306,7 +283,6 @@ static struct i2c_driver adjd_s311_driver = {
> >               .name   = ADJD_S311_DRV_NAME,
> >       },
> >       .probe          = adjd_s311_probe,
> > -     .remove         = adjd_s311_remove,
> >       .id_table       = adjd_s311_id,
> >  };
> >  module_i2c_driver(adjd_s311_driver);
>