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

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Date:   Mon, 27 Apr 2020 16:10:57 +0300
From:   Alexandru Ardelean <alexandru.ardelean@...log.com>
To:     <linux-iio@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC:     <lars@...afoo.de>, <jic23@...nel.org>, <pmeerw@...erw.net>,
        "Alexandru Ardelean" <alexandru.ardelean@...log.com>
Subject: [PATCH v6 3/6] 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 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,
+	.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);
 
-- 
2.17.1