Re: [PATCH v2] serial: imx: Fix handling of TC irq in combination with DMA

[Greg Kroah-Hartman]

On Tue, Jun 09, 2020 at 07:23:40AM +0000, Schrempf Frieder wrote:
> From: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
> 
> commit 1866541492641c02874bf51f9d8712b5510f2c64 upstream
> 
> When using RS485 half duplex the Transmitter Complete irq is needed to
> determine the moment when the transmitter can be disabled. When using
> DMA this irq must only be enabled when DMA has completed to transfer all
> data. Otherwise the CPU might busily trigger this irq which is not
> properly handled and so the also pending irq for the DMA transfer cannot
> trigger.
> 
> Cc: <stable@xxxxxxxxxxxxxxx> # v4.14.x
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> [Backport to v4.14]
> Signed-off-by: Frieder Schrempf <frieder.schrempf@xxxxxxxxxx>
> ---
> When using RS485 with DMA enabled simply transmitting some data on our
> i.MX6ULL based boards often freezes the system completely. The higher
> the baudrate, the easier it is to reproduce the issue. To test this I
> simply used:
> 
> stty -F /dev/ttymxc1 speed 115200
> while true; do echo TEST > /dev/ttymxc1; done
> 
> Without the patch this leads to an almost immediate system freeze,
> with the patch applied, everything keeps working as expected. 
> ---
>  drivers/tty/serial/imx.c | 22 ++++++++++++++++++----
>  1 file changed, 18 insertions(+), 4 deletions(-)

Now queued up, thanks.

greg k-h