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

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Message-ID: <20210703185007.2c2283f4@jic23-huawei>
Date:   Sat, 3 Jul 2021 18:50:07 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Alexandru Ardelean <aardelean@...iqon.com>
Cc:     linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
        pmeerw@...erw.net
Subject: Re: [PATCH] iio: light: adjd_s311: convert to device-managed
 functions

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 */
} scan;

Inside the priv structure should work nicely.


>  	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);