On 04/29/2015 01:18 PM, Octavian Purdila wrote:
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
Since there is no asynchronous queue for commands to be executed in IIO
adding a asynchronous completion event doesn't make too much sense. This is
something that needs to be handled at the HAL level.
The HAL needs to have a queue of commands that need to be executed where new
events can be added asynchronously, then has a loop which goes through the
commands in the queue and executes them, and once executed generated the
appropriate completion event.
I really wish that document would specify what is actually meant by flush.
Copy the FIFO content to a software buffer or discard the FIFO content.
Signed-off-by: Octavian Purdila <octavian.purd...@intel.com>
---
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-...@vger.kernel.org
+Description:
+ 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.
I'd prefer this to be handled through the normal read() API rather than
having a side channel for it. Big question is how though. We could specify
that reading in O_NONBLOCK mode will always read data if it is available and
not only if it is above the watermark threshold.
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