Hi Lukas, Lino, please let me know when I could test again with an "official" linux kernel, instead of using my local patch. Bests Jochen > On 02/01/2022 19:28 Lukas Wunner <lukas@xxxxxxxxx> wrote: > > > On Sun, Jan 02, 2022 at 04:06:53PM +0100, Lino Sanfilippo wrote: > > On 02.01.22 at 11:07, Lukas Wunner wrote: > > > On Fri, Dec 31, 2021 at 05:15:14PM +0000, jmades wrote: > > > > --- a/drivers/tty/serial/amba-pl011.c > > > > +++ b/drivers/tty/serial/amba-pl011.c > > > > @@ -1646,8 +1646,12 @@ static void pl011_set_mctrl(struct uart_port *port, unsigned int mctrl) > > > > container_of(port, struct uart_amba_port, port); > > > > unsigned int cr; > > > > > > > > - if (port->rs485.flags & SER_RS485_ENABLED) > > > > - mctrl &= ~TIOCM_RTS; > > > > + if (port->rs485.flags & SER_RS485_ENABLED) { > > > > + if (port->rs485.flags & SER_RS485_RTS_AFTER_SEND) > > > > + mctrl &= ~TIOCM_RTS; > > > > + else > > > > + mctrl |= TIOCM_RTS; > > > > + } > > > > > > > > cr = pl011_read(uap, REG_CR); > > > > Does this logic really have to be implemented in the driver? > > No, it doesn't have to be and indeed I'm working towards consolidating > it in the serial core with this collection of patches: > > https://git.kernel.org/gregkh/tty/c/d3b3404df318 > https://lore.kernel.org/all/f49f945375f5ccb979893c49f1129f51651ac738.1641129062.git.lukas@xxxxxxxxx > https://lore.kernel.org/all/e22089ab49e6e78822c50c8c4db46bf3ee885623.1641129328.git.lukas@xxxxxxxxx > https://lore.kernel.org/all/bceeaba030b028ed810272d55d5fc6f3656ddddb.1641129752.git.lukas@xxxxxxxxx > https://github.com/l1k/linux/commit/532ef2ad757f > > The last of these removes the rs485 logic from pl011_set_mctrl(). > I'll post it once the others (and Jochen Mades' patch) have landed. > > Even though the logic is eventually removed from pl011_set_mctrl(), > Jochen's patch makes sense as a backportable fix for v5.15. > > > > It looks as if the serial core already takes RS485 into account before > > calling set_mctrls(). At least I get the impression when looking > > at uart_tiocmset() and uart_port_dtr_rts(). Also other drivers like imx > > simply seem to ignore RTS in case of RS485. > > The logic in uart_port_dtr_rts() is broken. That's fixed by d3b3404df318, > which is queued up in tty-next for v5.17. > > The pl011 driver papered over it with its own rs485-specific logic in > pl011_set_mctrl(). But as Jochen Mades correctly pointed out, that > only worked correctly if RTS is driven high on idle. > > > The logic in uart_tiocmset() is correct, but not sufficient because > uart_throttle(), uart_unthrottle and uart_set_termios() need to become > rs485-aware as well. That's also addressed by the above-linked > GitHub commit. > > Thanks, > > Lukas