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iio: add watermark logic to iio read and poll

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Currently the IIO buffer blocking read only wait until at least one
data element is available.
This patch makes the reader sleep until enough data is collected before
returning to userspace. This should limit the read() calls count when
trying to get data in batches.

Co-author: Yannick Bedhomme <yannick.bedhomme@mobile-devices.fr>
Signed-off-by: Josselin Costanzi <josselin.costanzi@mobile-devices.fr>
[rebased and remove buffer timeout]
Signed-off-by: Octavian Purdila <octavian.purdila@intel.com>
Reviewed-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
This commit is contained in:
Josselin Costanzi
2015-03-22 20:33:38 +02:00
committed by Jonathan Cameron
parent 9444a300c2
commit 37d3455672
5 changed files with 132 additions and 28 deletions
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15
Documentation/ABI/testing/sysfs-bus-iio
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@@ -1280,3 +1280,18 @@ Contact: linux-iio@vger.kernel.org
Description:
Specifies number of seconds in which we compute the steps
that occur in order to decide if the consumer is making steps.
What: /sys/bus/iio/devices/iio:deviceX/buffer/watermark
KernelVersion: 4.2
Contact: linux-iio@vger.kernel.org
Description:
A single positive integer specifying the maximum number of scan
elements to wait for.
Poll will block until the watermark is reached.
Blocking read will wait until the minimum between the requested
read amount or the low water mark is available.
Non-blocking read will retrieve the available samples from the
buffer even if there are less samples then watermark level. This
allows the application to block on poll with a timeout and read
the available samples after the timeout expires and thus have a
maximum delay guarantee.