On Mon, 17 Oct 2022, Uwe Kleine-König wrote: > On Mon, Oct 17, 2022 at 03:27:19PM +0300, Ilpo Järvinen wrote: > > 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. > > AFAICT the irq doesn't stop being pending without the read. At least the comment in 8250_dw says it has similar irq loop behavior if nothing is read when IIR_RX_TIMEOUT is seen w/o DR. The others IIR_RX_TIMEOUT comments don't state it so it could be either way (but if I'd hazard a guess w/o history dig, they'll probably irq loop as well). > But yes, > there are some details to research/explain, for example what is read > from the data register and if this byte is valid or not. > > Also without status having the DR (or BI) bit set, UART_IIR_RX_TIMEOUT > doesn't kick in?! I didn't understand what you were trying to ask/note here. -- i.
