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Date:   Sun, 3 May 2020 16:39:26 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Alexandru Ardelean <alexandru.ardelean@...log.com>
Cc:     <linux-iio@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <lars@...afoo.de>, <pmeerw@...erw.net>
Subject: Re: [PATCH v6 3/6] iio: core: register chardev only if needed

On Mon, 27 Apr 2020 16:10:57 +0300
Alexandru Ardelean <alexandru.ardelean@...log.com> wrote:

> The final intent is to localize all buffer ops into the
> industrialio-buffer.c file, to be able to add support for multiple buffers
> per IIO device.
> 
> We only need a chardev if we need to support buffers and/or events.
> 
> With this change, a chardev will be created only if an IIO buffer is
> attached OR an event_interface is configured.
> 
> Otherwise, no chardev will be created, and the IIO device will get
> registered with the 'device_add()' call.
> 
> Quite a lot of IIO devices don't really need a chardev, so this is a minor
> improvement to the IIO core, as the IIO device will take up (slightly)
> fewer resources.
> 
> Signed-off-by: Alexandru Ardelean <alexandru.ardelean@...log.com>
> ---
>  drivers/iio/industrialio-core.c | 25 ++++++++++++++++++++++---
>  1 file changed, 22 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
> index 32c489139cd2..51e279c60793 100644
> --- a/drivers/iio/industrialio-core.c
> +++ b/drivers/iio/industrialio-core.c
> @@ -1682,6 +1682,15 @@ static int iio_check_unique_scan_index(struct iio_dev *indio_dev)
>  
>  static const struct iio_buffer_setup_ops noop_ring_setup_ops;
>  
> +static const struct file_operations iio_event_fileops = {
> +	.owner = THIS_MODULE,
> +	.llseek = noop_llseek,
> +	.unlocked_ioctl = iio_event_ioctl_wrapper,

Unfortunately this doesn't exist until the next patch...

> +	.compat_ioctl = compat_ptr_ioctl,
> +	.open = iio_chrdev_open,
> +	.release = iio_chrdev_release,
> +};
> +
>  int __iio_device_register(struct iio_dev *indio_dev, struct module *this_mod)
>  {
>  	int ret;
> @@ -1732,11 +1741,18 @@ int __iio_device_register(struct iio_dev *indio_dev, struct module *this_mod)
>  		indio_dev->setup_ops == NULL)
>  		indio_dev->setup_ops = &noop_ring_setup_ops;
>  
> -	cdev_init(&indio_dev->chrdev, &iio_buffer_fileops);
> +	if (indio_dev->buffer)
> +		cdev_init(&indio_dev->chrdev, &iio_buffer_fileops);
> +	else if (indio_dev->event_interface)
> +		cdev_init(&indio_dev->chrdev, &iio_event_fileops);
>  
>  	indio_dev->chrdev.owner = this_mod;
>  
> -	ret = cdev_device_add(&indio_dev->chrdev, &indio_dev->dev);
> +	if (indio_dev->buffer || indio_dev->event_interface)
> +		ret = cdev_device_add(&indio_dev->chrdev, &indio_dev->dev);
> +	else
> +		ret = device_add(&indio_dev->dev);
> +
>  	if (ret < 0)
>  		goto error_unreg_eventset;
>  
> @@ -1760,7 +1776,10 @@ EXPORT_SYMBOL(__iio_device_register);
>   **/
>  void iio_device_unregister(struct iio_dev *indio_dev)
>  {
> -	cdev_device_del(&indio_dev->chrdev, &indio_dev->dev);
> +	if (indio_dev->buffer || indio_dev->event_interface)
> +		cdev_device_del(&indio_dev->chrdev, &indio_dev->dev);
> +	else
> +		device_del(&indio_dev->dev);
>  
>  	mutex_lock(&indio_dev->info_exist_lock);
>  

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