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

From: Philipp Puschmann <philipp.puschmann@emlix.com>
To: Robin Gong <yibin.gong@nxp.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Cc: "vkoul@kernel.org" <vkoul@kernel.org>,
	"dan.j.williams@intel.com" <dan.j.williams@intel.com>,
	"shawnguo@kernel.org" <shawnguo@kernel.org>,
	"s.hauer@pengutronix.de" <s.hauer@pengutronix.de>,
	"kernel@pengutronix.de" <kernel@pengutronix.de>,
	"festevam@gmail.com" <festevam@gmail.com>,
	dl-linux-imx <linux-imx@nxp.com>,
	"gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
	"jslaby@suse.com" <jslaby@suse.com>,
	"dmaengine@vger.kernel.org" <dmaengine@vger.kernel.org>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
	"linux-serial@vger.kernel.org" <linux-serial@vger.kernel.org>
Subject: Re: [PATCH 0/4] Fix UART DMA freezes for iMX6
Date: Mon, 16 Sep 2019 15:41:49 +0200	[thread overview]
Message-ID: <29d03762-866a-4fdc-eddb-e24f6e631412@emlix.com> (raw)
In-Reply-To: <VE1PR04MB66383FAB08506993B305AC8D898C0@VE1PR04MB6638.eurprd04.prod.outlook.com>

Am 16.09.19 um 10:02 schrieb Robin Gong:
> On 2019/9/11 Philipp Puschmann <philipp.puschmann@emlix.com> 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 <linux@arm.linux.org.uk>
> 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
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