[RFC PATCH 2/3] iio: allow better control for flushing the hardware fifo

From: Octavian Purdila
Date: Wed Apr 29 2015 - 07:19:22 EST

Some applications need to be able to flush [1] the hardware fifo of
the device and to receive events of when that happened [2] so that it
can ignore stale data.

This patch adds a new event (IIO_EV_TYPE_HWFIFO_FLUSHED) that should
be sent to userspace when a flush has been completed. The application
will be able to identify which are the samples to ignore based on the
timestamp of the event.

To allow applications to accurately generate a hardware fifo flush on
demand, this patch also adds a new sysfs entry that triggers a
hardware fifo flush when written to.

[1] https://source.android.com/devices/sensors/hal-interface.html#flush_sensor
[2] https://source.android.com/devices/sensors/hal-interface.html#metadata_flush_complete_events

Signed-off-by: Octavian Purdila <octavian.purdila@xxxxxxxxx>
Documentation/ABI/testing/sysfs-bus-iio | 11 +++++++++++
include/linux/iio/sysfs.h | 3 +++
include/uapi/linux/iio/types.h | 1 +
3 files changed, 15 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-bus-iio b/Documentation/ABI/testing/sysfs-bus-iio
index 866b4ec..bb4d8de 100644
--- a/Documentation/ABI/testing/sysfs-bus-iio
+++ b/Documentation/ABI/testing/sysfs-bus-iio
@@ -1375,3 +1375,14 @@ Description:
The emissivity ratio of the surface in the field of view of the
contactless temperature sensor. Emissivity varies from 0 to 1,
with 1 being the emissivity of a black body.
+What: /sys/bus/iio/devices/iio:deviceX/buffer/hwfifo_flush
+KernelVersion: 4.2
+Contact: linux-iio@xxxxxxxxxxxxxxx
+ Write only entry that accepts a single strictly positive integer
+ specifying the number of samples to flush from the hardware fifo
+ to the device buffer. When the flush is completed an
+ IIO_EV_TYPE_HWFIFO_FLUSHED event is generated. The event has the
+ timestamp equal with the timestamp of last sample that was
+ flushed from the hardware fifo.
diff --git a/include/linux/iio/sysfs.h b/include/linux/iio/sysfs.h
index 8822bab..8fcc25b 100644
--- a/include/linux/iio/sysfs.h
+++ b/include/linux/iio/sysfs.h
@@ -136,4 +136,7 @@ struct iio_const_attr {
#define IIO_DEV_ATTR_HWFIFO_WATERMARK(_hwfifo_get_wm) \
IIO_DEVICE_ATTR(hwfifo_watermark, S_IRUGO, _hwfifo_get_wm, NULL, 0)

+#define IIO_DEV_ATTR_HWFIFO_FLUSH(_hwfifo_flush) \
+ IIO_DEVICE_ATTR(hwfifo_flush, S_IWUSR, NULL, _hwfifo_flush, 0)
#endif /* _INDUSTRIAL_IO_SYSFS_H_ */
diff --git a/include/uapi/linux/iio/types.h b/include/uapi/linux/iio/types.h
index 5c46019..4600157 100644
--- a/include/uapi/linux/iio/types.h
+++ b/include/uapi/linux/iio/types.h
@@ -79,6 +79,7 @@ enum iio_event_type {

enum iio_event_direction {

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