Re: [PATCH v2] iio: core: register chardev only if needed

[Jonathan Cameron <jic23@kernel.org>]

On Tue, 14 Apr 2020 11:36:56 +0300
Alexandru Ardelean <alexandru.ardelean@analog.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:
> 1. if there is an IIO buffer attached OR
> 2. if there is an event_interface configured
> 
> Otherwise, no chardev will be created.
> 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 fewer
> resources.
> 
> Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
> ---
> 
> Changelog v1 -> v2:
> * split away from series 'iio: core,buffer: re-organize chardev creation';
>   i'm getting the feeling that this has some value on it's own;
>   no idea if it needs 'Fixes' tag; it is a bit fuzzy to point to a patch
>   which this would be fixed by this; i'm guessing it would be fine
>   without one

I'd argue it's an 'optimization' rather than a fix :)

Still looks good to me but I'd like it to sit for a little while to
see if anyone points out something we are both missing!

Thanks for tidying this up.

Jonathan

> 
>  drivers/iio/industrialio-core.c | 17 +++++++++++++++--
>  1 file changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
> index f4daf19f2a3b..32e72d9fd1e9 100644
> --- a/drivers/iio/industrialio-core.c
> +++ b/drivers/iio/industrialio-core.c
> @@ -1676,6 +1676,15 @@ 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 = {
> +	.release = iio_chrdev_release,
> +	.open = iio_chrdev_open,
> +	.owner = THIS_MODULE,
> +	.llseek = noop_llseek,
> +	.unlocked_ioctl = iio_ioctl,
> +	.compat_ioctl = compat_ptr_ioctl,
> +};
> +
>  int __iio_device_register(struct iio_dev *indio_dev, struct module *this_mod)
>  {
>  	int ret;
> @@ -1726,7 +1735,10 @@ 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;
>  
> @@ -1754,7 +1766,8 @@ 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);
>  
>  	mutex_lock(&indio_dev->info_exist_lock);
>