linux-kernel - Re: [PATCH v6 3/6] iio: core: register chardev only if needed

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Date:   Mon, 4 May 2020 06:46:19 +0000
From:   "Ardelean, Alexandru" <alexandru.Ardelean@...log.com>
To:     "jic23@...nel.org" <jic23@...nel.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
        "pmeerw@...erw.net" <pmeerw@...erw.net>,
        "lars@...afoo.de" <lars@...afoo.de>
Subject: Re: [PATCH v6 3/6] iio: core: register chardev only if needed

On Sun, 2020-05-03 at 16:39 +0100, Jonathan Cameron wrote:
> [External]
> 
> 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...

crap;
i copied this from the wrong place when i re-ordered this, and forgot to run a
build on each patchset

will fix

> 
> > +	.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);
> >