linux-kernel - Re: [PATCH v3 1/5] iio: core: register buffer fileops only if buffer present

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Date:   Tue, 14 Apr 2020 05:20:09 +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>,
        "lars@...afoo.de" <lars@...afoo.de>
Subject: Re: [PATCH v3 1/5] iio: core: register buffer fileops only if buffer
 present

On Mon, 2020-04-13 at 16:47 +0100, Jonathan Cameron wrote:
> [External]
> 
> On Fri, 10 Apr 2020 17:17:25 +0300
> Alexandru Ardelean <alexandru.ardelean@...log.com> wrote:
> 
> > The 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 still need to allocate a chardev in __iio_device_register() to be able
> > to pass event ioctl commands. So, if the IIO device has no buffer, we
> > create the legacy chardev for the event ioctl() command.
> > 
> > Signed-off-by: Alexandru Ardelean <alexandru.ardelean@...log.com>
> 
> Whilst we are here, can we avoid allocating the chardev at all if
> we have neither buffer support, nor events?  So don't add the chrdev to the
> device.

That should happen after patch 5/5.
If there aren't any buffers, and 'indio_dev->event_interface' is NULL, no
chardev should exist.

Maybe I can reduce this, given the fact that this goes away into files later.
I did things in very-small incremental steps that I later squashed.

This patch kind of highlights an intermediate step towards the final rework
[moving chardevs into files]

> 
> That covers quite a wide range of slow devices and is a nice incidental
> improvement (to be honest I'd forgotten we actually created a chardev
> in those circumstance :(
> 
> Jonathan
> 
> > ---
> >  drivers/iio/industrialio-core.c | 14 +++++++++++++-
> >  1 file changed, 13 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-
> > core.c
> > index 157d95a24faa..c8c074602709 100644
> > --- a/drivers/iio/industrialio-core.c
> > +++ b/drivers/iio/industrialio-core.c
> > @@ -1707,6 +1707,15 @@ 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;
> > @@ -1757,7 +1766,10 @@ 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
> > +		cdev_init(&indio_dev->chrdev, &iio_event_fileops);
> >  
> >  	indio_dev->chrdev.owner = this_mod;
> >