iio: trigger: allow immutable triggers to be assigned

There are times when an assigned trigger to a device shouldn't ever
change after intialization.

Examples of this being used is when an provider device has a trigger
that is assigned to an ADC, which uses it populate data into a callback
buffer.

Signed-off-by: Matt Ranostay <matt@ranostay.consulting>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

1 files changed, 20 insertions, 0 deletions

diff --git a/drivers/iio/industrialio-trigger.c b/drivers/iio/industrialio-trigger.c
index 7ad82fdd3e5b..3dde81e57e97 100644
--- a/drivers/iio/industrialio-trigger.c
+++ b/drivers/iio/industrialio-trigger.c
@@ -119,6 +119,22 @@ void iio_trigger_unregister(struct iio_trigger *trig_info)
 }
 EXPORT_SYMBOL(iio_trigger_unregister);
 
+int iio_trigger_set_immutable(struct iio_dev *indio_dev, struct iio_trigger *trig)
+{
+        if (!indio_dev || !trig)
+                return -EINVAL;
+
+        mutex_lock(&indio_dev->mlock);
+        WARN_ON(indio_dev->trig_readonly);
+
+        indio_dev->trig = iio_trigger_get(trig);
+        indio_dev->trig_readonly = true;
+        mutex_unlock(&indio_dev->mlock);
+
+        return 0;
+}
+EXPORT_SYMBOL(iio_trigger_set_immutable);
+
 /* Search for trigger by name, assuming iio_trigger_list_lock held */
 static struct iio_trigger *__iio_trigger_find_by_name(const char *name)
 {
@@ -384,6 +400,10 @@ static ssize_t iio_trigger_write_current(struct device *dev,
                 mutex_unlock(&indio_dev->mlock);
                 return -EBUSY;
         }
+        if (indio_dev->trig_readonly) {
+                mutex_unlock(&indio_dev->mlock);
+                return -EPERM;
+        }
         mutex_unlock(&indio_dev->mlock);
 
         trig = iio_trigger_find_by_name(buf, len);