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

[Andy Duan]

From: Philipp Puschmann <philipp.puschmann@xxxxxxxxx> 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@xxxxxxx>