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>

1 files changed, 16 insertions, 0 deletions

diff --git a/drivers/iio/industrialio-trigger.c b/drivers/iio/industrialio-trigger.c
index ba584b5e71f4..e1e104845e38 100644
--- a/drivers/iio/industrialio-trigger.c
+++ b/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++] =