iio: trigger: helpers to determine own trigger

This adds a helper function to the IIO trigger framework:

iio_trigger_using_own(): for an IIO device, this tells
  whether the device is using itself as a trigger.
  This is true if the indio device:
  (A) supplies a trigger and
  (B) has assigned its own buffer poll function to use this
      trigger.

This helper function is good when constructing triggered,
buffered drivers that can either use its own hardware *OR*
an external trigger such as a HRTimer or even the trigger from
a totally different sensor.

Under such circumstances it is important to know for example
if the timestamp from the same trigger hardware should be used
when populating the buffer: if iio_trigger_using_own() is true,
we can use this timestamp, else we need to pick a unique
timestamp directly in the trigger handler.

For this to work of course IIO devices registering hardware
triggers must follow the convention to set the parent device
properly, as as well as setting the parent of the IIO device
itself.

When a new poll function is attached, we check if the parent
device of the IIO of the poll function is the same as the
parent device of the trigger and in that case we conclude that
the hardware is using itself as trigger.

Cc: Giuseppe Barba <giuseppe.barba@st.com>
Cc: Denis Ciocca <denis.ciocca@st.com>
Cc: Crestez Dan Leonard <leonard.crestez@intel.com>
Cc: Gregor Boirie <gregor.boirie@parrot.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/industrialio-trigger.c

@@ -271,6 +271,14 @@ static int iio_trigger_attach_poll_func(struct iio_trigger *trig,
 			goto out_free_irq;
 	}
 
+	/*
+	 * Check if we just registered to our own trigger: we determine that
+	 * this is the case if the IIO device and the trigger device share the
+	 * same parent device.
+	 */
+	if (pf->indio_dev->dev.parent == trig->dev.parent)
+		trig->attached_own_device = true;
+
 	return ret;
 
 out_free_irq:
@@ -295,6 +303,8 @@ static int iio_trigger_detach_poll_func(struct iio_trigger *trig,
 		if (ret)
 			return ret;
 	}
+	if (pf->indio_dev->dev.parent == trig->dev.parent)
+		trig->attached_own_device = false;
 	iio_trigger_put_irq(trig, pf->irq);
 	free_irq(pf->irq, pf);
 	module_put(pf->indio_dev->info->driver_module);
@@ -701,6 +711,12 @@ void devm_iio_trigger_unregister(struct device *dev,
 }
 EXPORT_SYMBOL_GPL(devm_iio_trigger_unregister);
 
+bool iio_trigger_using_own(struct iio_dev *indio_dev)
+{
+	return indio_dev->trig->attached_own_device;
+}
+EXPORT_SYMBOL(iio_trigger_using_own);
+
 void iio_device_register_trigger_consumer(struct iio_dev *indio_dev)
 {
 	indio_dev->groups[indio_dev->groupcounter++] =

include/linux/iio/trigger.h

@@ -56,6 +56,9 @@ struct iio_trigger_ops {
  * @subirqs:		[INTERN] information about the 'child' irqs.
  * @pool:		[INTERN] bitmap of irqs currently in use.
  * @pool_lock:		[INTERN] protection of the irq pool.
+ * @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.
  **/
 struct iio_trigger {
 	const struct iio_trigger_ops	*ops;
@@ -73,6 +76,7 @@ struct iio_trigger {
 	struct iio_subirq subirqs[CONFIG_IIO_CONSUMERS_PER_TRIGGER];
 	unsigned long pool[BITS_TO_LONGS(CONFIG_IIO_CONSUMERS_PER_TRIGGER)];
 	struct mutex			pool_lock;
+	bool				attached_own_device;
 };
 
 
@@ -160,6 +164,13 @@ irqreturn_t iio_trigger_generic_data_rdy_poll(int irq, void *private);
 __printf(1, 2) struct iio_trigger *iio_trigger_alloc(const char *fmt, ...);
 void iio_trigger_free(struct iio_trigger *trig);
 
+/**
+ * iio_trigger_using_own() - tells us if we use our own HW trigger ourselves
+ * @indio_dev:  device to check
+ */
+bool iio_trigger_using_own(struct iio_dev *indio_dev);
+
+
 #else
 struct iio_trigger;
 struct iio_trigger_ops;