tree e49c8cfaa331800383c72e5277d2f06d0016f7bc
parent 77e6fe7fd2b7cba0bf2f2dc8cde51d7b9a35bf74
author Peter Senna Tschudin <peter.senna@collabora.com> 1491558324 +0200
committer Greg Kroah-Hartman <gregkh@linuxfoundation.org> 1491939403 +0200

imx-serial: Reduce RX DMA startup latency when opening for reading

Reduce RX DMA start latency for the first reception when port is opened
for reading. Instead of waiting for an interrupt signaling data on RX
FIFO or data too old on RX FIFO, start RX DMA immediately when the
serial port is opened for reading.

Before this patch, the average RX DMA latency for the first reception
was 42489 microseconds with a standard deviation of 25721 microseconds
in 36 samples.

After the patch the average RX DMA latency for the first reception, when
the serial port is opened for reading, is 653 microseconds with a
standard deviation of 294 microseconds in 36 samples.

Signed-off-by: Peter Senna Tschudin <peter.senna@collabora.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>