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

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Date:   Mon, 16 Sep 2019 14:10:18 +0000
From:   Andy Duan <fugang.duan@....com>
To:     Philipp Puschmann <philipp.puschmann@...ix.com>,
        Fabio Estevam <festevam@...il.com>,
        Robin Gong <yibin.gong@....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>,
        dl-linux-imx <linux-imx@....com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>
Subject: RE: [EXT] Re: [PATCH 0/4] Fix UART DMA freezes for iMX6

From: Philipp Puschmann <philipp.puschmann@...ix.com> Sent: Monday, September 16, 2019 9:55 PM
> 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.

For dma and uart, please to- me and yibin.gong@....com, thanks.

Andy