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

[Fabio Estevam]

[Adding Robin and Andy]

On Wed, Sep 11, 2019 at 11:50 AM Philipp Puschmann
<philipp.puschmann@xxxxxxxxx> 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
>
>  drivers/dma/imx-sdma.c   | 32 ++++++++++++++++++++++----------
>  drivers/tty/serial/imx.c |  5 ++---
>  2 files changed, 24 insertions(+), 13 deletions(-)
>
> --
> 2.23.0
>