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Message-ID: <55450C9E.4060409@metafoo.de> Date: Sat, 02 May 2015 19:42:54 +0200 From: Lars-Peter Clausen <lars@...afoo.de> To: Octavian Purdila <octavian.purdila@...el.com>, jic23@...nel.org CC: knaack.h@....de, pmeerw@...erw.net, linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org, adriana.reus@...el.com, linux-api@...r.kernel.org Subject: Re: [RFC PATCH 2/3] iio: allow better control for flushing the hardware fifo 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@...el.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-iio@...r.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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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