Regression: serial: imx: overrun errors on debug UART

[Ilpo Järvinen]

On Fri, 24 Mar 2023, Stefan Wahren wrote:

> Hi,
> 
> after switching to Linux 6.1.21 on our Tarragon board (i.MX6ULL SoC), we
> experience the following issues with the debug UART (115200 baud, 8N1, no
> hardware flow control):
> 
> - overrun errors if we paste in multiple text lines while system is idle
> - no reaction to single key strokes while system is on higher load
> 
> After reverting 7a637784d517 ("serial: imx: reduce RX interrupt frequency")
> the issue disappear.
> 
> Maybe it's worth to mention that the Tarragon board uses two additional
> application UARTs with similiar baud rates (9600 - 115200 baud, no hardware
> flow control) for RS485 communication, but there are no overrun errors (with
> and without the mention change).

This has come up earlier, see e.g.:

https://lore.kernel.org/linux-serial/20221003110850.GA28338@francesco-nb.int.toradex.com/

My somewhat uninformed suggestion: if the overrun problems mostly show up 
with console ports, maybe the trigger level could depend on the port 
being a console or not?


-- 
 i.