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

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Date:   Mon, 16 Sep 2019 15:55:04 +0200
From:   Philipp Puschmann <philipp.puschmann@...ix.com>
To:     Fabio Estevam <festevam@...il.com>,
        Robin Gong <yibin.gong@....com>,
        Fugang Duan <fugang.duan@....com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Vinod <vkoul@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <kernel@...gutronix.de>,
        NXP Linux Team <linux-imx@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>, dmaengine@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-serial@...r.kernel.org
Subject: Re: [PATCH 0/4] Fix UART DMA freezes for iMX6

Hi Fabio,

Am 12.09.19 um 20:23 schrieb Fabio Estevam:
> Hi Philipp,
> 
> Thanks for submitting these fixes.
> 
> On Wed, Sep 11, 2019 at 11:50 AM Philipp Puschmann
> <philipp.puschmann@...ix.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 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
> 
> I have some suggestions:
> 
> 1. Please split this in two series: one for dmaengine and other one for serial
> 
> 2. Please add Fixes tag when appropriate, so that the fixes can be
> backported to stable kernels.
> 
> 3. Please Cc Robin and Andy
> 
> Thanks
> 

Thanks for the hints. I will apply them if the contentual feedback is positive.

p.s. Did you forget to add Andy? I don't see a Andy in the to- and cc-list.