Subject: Re: [PATCH 0/4] Fix UART DMA freezes for iMX6

From: Philipp Puschmann <[email-masked]>
Date: Mon, 16 Sep 2019 15:41:49 +0200

Am 16.09.19 um 10:02 schrieb Robin Gong:
> On 2019/9/11 Philipp Puschmann <[email-masked]> 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 <[email-masked]>
> Date:   Wed Jun 25 13:00:33 2014 +0100
> 

Hi Robin, yes i have reproduced the Bluetooth issue with my test case with kernel 4.15
and the newest 5.3.0-rc8-next-20190915. My test-case includes several custom-boards
communicating via Bluetooth with each other. I see the error within seconds to few minutes.

>     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
> 

-- 

Philipp Puschmann, emlix GmbH, http://www.emlix.com
Fon +49 551 30664-0, Fax +49 551 30664-11
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