On Mon, 17 Oct 2022, Uwe Kleine-König wrote: > Hello, > > I have a system based on MPC8313ERDB here that in some situations gets > stuck in an irq loop. I have a reproducer here that works reliably. A > workaround is: > > diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c > index 45b8a59d937c..5ab32b6ba701 100644 > --- a/drivers/tty/serial/8250/8250_port.c > +++ b/drivers/tty/serial/8250/8250_port.c > @@ -2009,6 +2009,14 @@ int serial8250_handle_irq(struct uart_port *port, unsigned int iir) > > status = serial_port_in(port, UART_LSR); > > + /* > + * Sometimes a "Character time-out" (IID3:0 == 0xc) happens on MPC8313, > + * but LSR doesn't report "Data ready". To clear the former the receive > + * buffer must be read. It's unclear if the char read is valid or not. > + */ > + if ((iir & UART_IIR_ID) == UART_IIR_RX_TIMEOUT) > + status |= UART_LSR_DR; > + > /* > * If port is stopped and there are no error conditions in the > * FIFO, then don't drain the FIFO, as this may lead to TTY buffer > > I havn't debugged that further than written in the comment but I wonder > if this is a known issue (didn't find it in the errata though) and/or if > someone with hardware knowledge could confirm this to be a hardware > fault. > > Without feedback from NXP I'd look in more detail into that to for > example find out the timing and so maybe more hints about the hardware > and a better SW workaround/fix. > > Any input is very welcome. I find it bit odd you seem to assume w/o any justification that the data would be valid (that workaround will read one byte and consider it valid, no?). According to the comments & workarounds to the same problem (just look for IIR_RX_TIMEOUT and you'll find a few), they all do dummy reads rather than assume the data is valid. -- i.
