[PATCH v3 1/2] iio: Allow triggers to be used as parent of others triggers

[Benjamin Gaignard]

Add "parent_trigger" sysfs attribute to iio trigger to be able
to set a parent to the current trigger.
Parent trigger edges or levels could be used to control current
trigger status for example to start, stop or reset it.

Introduce validate_trigger function in iio_trigger_ops which does
the same than validate_device but with a trigger as second parameter.
Driver must implement this function and add dev_attr_parent_trigger
in their trigger attribute group to be able to use parent trigger
feature.

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@xxxxxx>

version 3:
- try to provide better description of parent_trigger usages

version 2:
- add comment about parent trigger usage
- parent trigger attribute must be set the driver no more by IIO core
---
 .../ABI/testing/sysfs-bus-iio-trigger-sysfs        | 15 +++++
 drivers/iio/industrialio-trigger.c                 | 69 ++++++++++++++++++++++
 include/linux/iio/trigger.h                        |  7 ++-
 3 files changed, 90 insertions(+), 1 deletion(-)

diff --git a/Documentation/ABI/testing/sysfs-bus-iio-trigger-sysfs b/Documentation/ABI/testing/sysfs-bus-iio-trigger-sysfs
index 04ac623..1e7fc40 100644
--- a/Documentation/ABI/testing/sysfs-bus-iio-trigger-sysfs
+++ b/Documentation/ABI/testing/sysfs-bus-iio-trigger-sysfs
@@ -40,3 +40,18 @@ Description:
 		associated file, representing the id of the trigger that needs
 		to be removed. If the trigger can't be found, an invalid
 		argument message will be returned to the user.
+
+What:		/sys/bus/iio/devices/triggerX/parent_trigger
+KernelVersion:	4.12
+Contact:	linux-iio@xxxxxxxxxxxxxxx
+Description:
+		This attribute is used to set a trigger as parent for the
+		current trigger. If the trigger can't use the parent an
+		invalid argument message will be returned.
+		Parent trigger edges or levels could be used to control current
+		trigger. For example current trigger could be started on parent
+		rising edges or be enabled only when parent trigger level is
+		high.
+		Since there is many ways to use parent edges and levels to
+		control current trigger behavoir an additional custom sysfs
+		attribute may be needed to describe those control modes.
diff --git a/drivers/iio/industrialio-trigger.c b/drivers/iio/industrialio-trigger.c
index 978729f..9891fb2 100644
--- a/drivers/iio/industrialio-trigger.c
+++ b/drivers/iio/industrialio-trigger.c
@@ -58,6 +58,74 @@ static ssize_t iio_trigger_read_name(struct device *dev,
 
 static DEVICE_ATTR(name, S_IRUGO, iio_trigger_read_name, NULL);
 
+/**
+ * iio_trigger_read_parent() - trigger consumer sysfs query parent trigger
+ * @dev:	device associated with an industrial I/O trigger
+ * @attr:	pointer to the device_attribute structure that
+ *		is being processed
+ * @buf:	buffer where the current trigger name will be printed into
+ *
+ * Return: a negative number on failure, the number of characters written
+ *	   on success or 0 if no trigger is available
+ */
+static ssize_t iio_trigger_read_parent(struct device *dev,
+				       struct device_attribute *attr,
+				       char *buf)
+{
+	struct iio_trigger *trig = to_iio_trigger(dev);
+
+	if (trig->parent_trigger)
+		return sprintf(buf, "%s\n", trig->parent_trigger->name);
+
+	return 0;
+}
+
+static struct iio_trigger *iio_trigger_find_by_name(const char *name,
+						    size_t len);
+
+/**
+ * iio_trigger_write_parent() - trigger consumer sysfs set parent trigger
+ * @dev:	device associated with an industrial I/O trigger
+ * @attr:	device attribute that is being processed
+ * @buf:	string buffer that holds the name of the trigger
+ * @len:	length of the trigger name held by buf
+ *
+ * Return: negative error code on failure or length of the buffer
+ *	   on success
+ */
+static ssize_t iio_trigger_write_parent(struct device *dev,
+					struct device_attribute *attr,
+					const char *buf,
+					size_t len)
+{
+	struct iio_trigger *parent;
+	struct iio_trigger *child = to_iio_trigger(dev);
+	int ret;
+
+	if (!child->ops->validate_trigger)
+		return -EINVAL;
+
+	if (atomic_read(&child->use_count))
+		return -EBUSY;
+
+	parent = iio_trigger_find_by_name(buf, len);
+
+	if (parent == child->parent_trigger)
+		return len;
+
+	ret = child->ops->validate_trigger(child, parent);
+	if (ret)
+		return ret;
+
+	child->parent_trigger = parent;
+
+	return len;
+}
+
+DEVICE_ATTR(parent_trigger, S_IRUGO | S_IWUSR,
+	    iio_trigger_read_parent, iio_trigger_write_parent);
+EXPORT_SYMBOL_GPL(dev_attr_parent_trigger);
+
 static struct attribute *iio_trig_dev_attrs[] = {
 	&dev_attr_name.attr,
 	NULL,
@@ -440,6 +508,7 @@ static ssize_t iio_trigger_write_current(struct device *dev,
 						     indio_dev->pollfunc_event);
 		iio_trigger_put(oldtrig);
 	}
+
 	if (indio_dev->trig) {
 		iio_trigger_get(indio_dev->trig);
 		if (indio_dev->modes & INDIO_EVENT_TRIGGERED)
diff --git a/include/linux/iio/trigger.h b/include/linux/iio/trigger.h
index ea08302..efa2983 100644
--- a/include/linux/iio/trigger.h
+++ b/include/linux/iio/trigger.h
@@ -20,6 +20,7 @@ struct iio_subirq {
 
 struct iio_dev;
 struct iio_trigger;
+extern struct device_attribute dev_attr_parent_trigger;
 
 /**
  * struct iio_trigger_ops - operations structure for an iio_trigger.
@@ -29,6 +30,7 @@ struct iio_subirq {
  *			use count is zero (may be NULL)
  * @validate_device:	function to validate the device when the
  *			current trigger gets changed.
+ * @validate_trigger:	function to validate the parent trigger (may be NULL)
  *
  * This is typically static const within a driver and shared by
  * instances of a given device.
@@ -39,9 +41,10 @@ struct iio_trigger_ops {
 	int (*try_reenable)(struct iio_trigger *trig);
 	int (*validate_device)(struct iio_trigger *trig,
 			       struct iio_dev *indio_dev);
+	int (*validate_trigger)(struct iio_trigger *trig,
+				struct iio_trigger *parent);
 };
 
-
 /**
  * struct iio_trigger - industrial I/O trigger device
  * @ops:		[DRIVER] operations structure
@@ -59,6 +62,7 @@ struct iio_trigger_ops {
  * @attached_own_device:[INTERN] if we are using our own device as trigger,
  *			i.e. if we registered a poll function to the same
  *			device as the one providing the trigger.
+ * @parent_trigger:	[INTERN] parent trigger
  **/
 struct iio_trigger {
 	const struct iio_trigger_ops	*ops;
@@ -77,6 +81,7 @@ struct iio_trigger {
 	unsigned long pool[BITS_TO_LONGS(CONFIG_IIO_CONSUMERS_PER_TRIGGER)];
 	struct mutex			pool_lock;
 	bool				attached_own_device;
+	struct iio_trigger		*parent_trigger;
 };
 
 
-- 
1.9.1