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.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 +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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