Re: [PATCH v5 0/3] Fix UART DMA freezes for i.MX SOCs

[Adam Ford <aford173@gmail.com>]

On Mon, Sep 23, 2019 at 8:58 AM 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 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.
>

Using the 4.19.y branch, this seems to working just fine for me with an i.MX6Q
with WL1837MOD Bluetooth connected to UART2.  I am still seeing some
timeouts with 5.3, but I'm going to continue to run some tests.

Tested-by: Adam Ford <aford173@gmail.com> #imx6q w/ 4.19 Kernel

> Signed-off-by: Philipp Puschmann <philipp.puschmann@emlix.com>
> Reviewed-by: Fugang Duan <fugang.duan@nxp.com>
>
> ---
>
> Changelog v5:
>  - join with patch version from Jan Luebbe
>  - adapt comments and patch descriptions
>  - add Reviewed-by
>
> 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 | 37 +++++++++++++++++++++++++++----------
>  1 file changed, 27 insertions(+), 10 deletions(-)
>
> --
> 2.23.0
>
>
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