linux-kernel - RE: [EXT] [PATCH v4 0/3] Fix UART DMA freezes for i.MX SOCs

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Message-ID: <VI1PR0402MB36002C1C1E5A48EBA2385406FF880@VI1PR0402MB3600.eurprd04.prod.outlook.com>
Date:   Fri, 20 Sep 2019 02:44:33 +0000
From:   Andy Duan <fugang.duan@....com>
To:     Philipp Puschmann <philipp.puschmann@...ix.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Robin Gong <yibin.gong@....com>,
        "l.stach@...gutronix.de" <l.stach@...gutronix.de>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "vkoul@...nel.org" <vkoul@...nel.org>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "festevam@...il.com" <festevam@...il.com>,
        dl-linux-imx <linux-imx@....com>,
        "dmaengine@...r.kernel.or" <dmaengine@...r.kernel.or>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: RE: [EXT] [PATCH v4 0/3] Fix UART DMA freezes for i.MX SOCs

From: Philipp Puschmann <philipp.puschmann@...ix.com> Sent: Thursday, September 19, 2019 10:30 PM
> 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 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 manually retrigger the sdma script for this channel and by this
> dissolve the freeze.
> 
> While this seems to work fine so far, it may come to buffer overruns when the
> channel - even temporary - is stopped. This case has to be addressed by
> device drivers by increasing the number of DMA periods.
> 
> 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.
> 
> Changelog v4:
>  - fixed the fixes tags
> 
> Changelog v3:
>  - fixes typo in dma_wmb
>  - add fixes tags
> 
> Changelog v2:
>  - adapt title (this patches are not only for i.MX6)
>  - improve some comments and patch descriptions
>  - add a dma_wb() around BD_DONE flag
>  - add Reviewed-by tags
>  - split off  "serial: imx: adapt rx buffer and dma periods"
> 
> Philipp Puschmann (3):
>   dmaengine: imx-sdma: fix buffer ownership
>   dmaengine: imx-sdma: fix dma freezes
>   dmaengine: imx-sdma: drop redundant variable
> 
>  drivers/dma/imx-sdma.c | 32 ++++++++++++++++++++++----------
>  1 file changed, 22 insertions(+), 10 deletions(-)
> 
> --
> 2.23.0

The patch set look fine that is really to fix some corner issue from the logical view.

Reviewed-by: Fugang Duan <fugang.duan@....com>