linux-kernel - [PATCH v2] iio: core: register chardev only if needed

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Message-ID: <20200414083656.7696-1-alexandru.ardelean@analog.com>
Date:   Tue, 14 Apr 2020 11:36:56 +0300
From:   Alexandru Ardelean <alexandru.ardelean@...log.com>
To:     <linux-iio@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC:     <jic23@...nel.org>,
        Alexandru Ardelean <alexandru.ardelean@...log.com>
Subject: [PATCH v2] iio: core: register chardev only if needed

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@...log.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

 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);
 
-- 
2.17.1