On 02.01.22 at 19:28, Lukas Wunner 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 for this information. I have one or two patches prepared a while ago that aim into a similar direction (move RS485 related code out of the drivers into the serial core). I will send them in the next days. Best regards, Lino