Re: [PATCH 5.15] serial: stm32: rework RX over DMA

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Thu, Jun 20, 2024 at 05:26:57PM +0200, Dario Binacchi wrote:
> From: Erwan Le Ray <erwan.leray@foss.st.com>
> 
> commit 33bb2f6ac3088936b7aad3cab6f439f91af0223c upstream.
> 
> This patch reworks RX support over DMA to improve reliability:
> - change dma buffer cyclic configuration by using 2 periods. DMA buffer
> data are handled by a flip-flop between the 2 periods in order to avoid
> risk of data loss/corruption
> - change the size of dma buffer to 4096 to limit overruns
> - add rx errors management (breaks, parity, framing and overrun).
>   When an error occurs on the uart line, the dma request line is masked at
>   HW level. The SW must 1st clear DMAR (dma request line enable), to
>   handle the error, then re-enable DMAR to recover. So, any correct data
>   is taken from the DMA buffer, before handling the error itself. Then
>   errors are handled from RDR/ISR/FIFO (e.g. in PIO mode). Last, DMA
>   reception is resumed.
> - add a condition on DMA request line in DMA RX routines in order to
> switch to PIO mode when no DMA request line is disabled, even if the DMA
> channel is still enabled.
>   When the UART is wakeup source and is configured to use DMA for RX, any
>   incoming data that wakes up the system isn't correctly received.
>   At data reception, the irq_handler handles the WUF irq, and then the
>   data reception over DMA.
>   As the DMA transfer has been terminated at suspend, and will be restored
>   by resume callback (which has no yet been called by system), the data
>   can't be received.
>   The wake-up data has to be handled in PIO mode while suspend callback
>   has not been called.
> 
> Signed-off-by: Valentin Caron <valentin.caron@foss.st.com>
> Signed-off-by: Erwan Le Ray <erwan.leray@foss.st.com>
> Link: https://lore.kernel.org/r/20211020150332.10214-3-erwan.leray@foss.st.com
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> [ dario: fix conflicts for backport to v5.15. From the [1] series, only the
>   first patch was applied to the v5.15 branch. This caused a regression in
>   character reception, which can be fixed by applying the second patch. The
>   patch has been tested on the stm32f469-disco board.
>   [1] https://lore.kernel.org/all/20211020150332.10214-1-erwan.leray@foss.st.com/. ]
> Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
> 
> ---
> 
>  drivers/tty/serial/stm32-usart.c | 206 ++++++++++++++++++++++++-------
>  drivers/tty/serial/stm32-usart.h |  12 +-
>  2 files changed, 165 insertions(+), 53 deletions(-)
> 

Now queued up, thanks.

greg k-h