[PATCH v2 01/12] iio: core: register chardev only if needed

[Alexandru Ardelean]

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.

In order to not create a chardev, we mostly just need to not initialize the
indio_dev->dev.devt field. If that is un-initialized, cdev_device_add()
behaves like device_add().

Signed-off-by: Alexandru Ardelean <alexandru.ardel...@analog.com>
---
 drivers/iio/industrialio-core.c | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
index 7db761afa578..0a6fd299a978 100644
--- a/drivers/iio/industrialio-core.c
+++ b/drivers/iio/industrialio-core.c
@@ -1761,6 +1761,15 @@ static const struct file_operations iio_buffer_fileops = 
{
        .release = iio_chrdev_release,
 };
 
+static const struct file_operations iio_event_fileops = {
+       .owner = THIS_MODULE,
+       .llseek = noop_llseek,
+       .unlocked_ioctl = iio_ioctl,
+       .compat_ioctl = compat_ptr_ioctl,
+       .open = iio_chrdev_open,
+       .release = iio_chrdev_release,
+};
+
 static int iio_check_unique_scan_index(struct iio_dev *indio_dev)
 {
        int i, j;
@@ -1788,6 +1797,7 @@ static const struct iio_buffer_setup_ops 
noop_ring_setup_ops;
 
 int __iio_device_register(struct iio_dev *indio_dev, struct module *this_mod)
 {
+       struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(indio_dev);
        int ret;
 
        if (!indio_dev->info)
@@ -1805,9 +1815,6 @@ int __iio_device_register(struct iio_dev *indio_dev, 
struct module *this_mod)
        if (ret < 0)
                return ret;
 
-       /* configure elements for the chrdev */
-       indio_dev->dev.devt = MKDEV(MAJOR(iio_devt), indio_dev->id);
-
        iio_device_register_debugfs(indio_dev);
 
        ret = iio_buffer_alloc_sysfs_and_mask(indio_dev);
@@ -1836,9 +1843,15 @@ 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 (iio_dev_opaque->event_interface)
+               cdev_init(&indio_dev->chrdev, &iio_event_fileops);
 
-       indio_dev->chrdev.owner = this_mod;
+       if (indio_dev->buffer || iio_dev_opaque->event_interface) {
+               indio_dev->dev.devt = MKDEV(MAJOR(iio_devt), indio_dev->id);
+               indio_dev->chrdev.owner = this_mod;
+       }
 
        ret = cdev_device_add(&indio_dev->chrdev, &indio_dev->dev);
        if (ret < 0)
-- 
2.17.1