On 2019/9/11 Philipp Puschmann [off-list ref] wrote:

For some years and since many kernel versions there are reports that RX
UART DMA channel stops working at one point. So far the usual workaround
was to disable RX DMA. This patches try to fix the underlying problem.

When a running sdma script does not find any usable destination buffer to put
its data into it just leads to stopping the channel being scheduled again. As
solution we we manually retrigger the sdma script for this channel and by this
dissolve the freeze.

While this seems to work fine so far a further patch in this series increases the
number of RX DMA periods for UART to reduce use cases running into such a
situation.

This patch series was tested with the current kernel and backported to kernel
4.15 with a special use case using a WL1837MOD via UART and provoking the

Hi Philipp, Could your Bluetooth issue be reproduce on latest linux-next? Or did
your kernel which can be reproduced include the below patch?

commit d1a792f3b4072bfac4150bb62aa34917b77fdb6d
Author: Russell King - ARM Linux [off-list ref]
Date:   Wed Jun 25 13:00:33 2014 +0100

    Update imx-sdma cyclic handling to report residue

hanging of UART RX DMA within seconds after starting a test application.
It resulted in well known
  "Bluetooth: hci0: command 0x0408 tx timeout"
errors and complete stop of UART data reception. Our Bluetooth traffic
consists of many independent small packets, mostly only a few bytes, causing
high usage of periods.


Philipp Puschmann (4):
  dmaengine: imx-sdma: fix buffer ownership
  dmaengine: imx-sdma: fix dma freezes
  serial: imx: adapt rx buffer and dma periods
  dmaengine: imx-sdma: drop redundant variable

 drivers/dma/imx-sdma.c   | 32 ++++++++++++++++++++++----------
 drivers/tty/serial/imx.c |  5 ++---
 2 files changed, 24 insertions(+), 13 deletions(-)

--
2.23.0

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