On Fri, Dec 31, 2021 at 05:15:14PM +0000, jmades wrote:
> Based on the "0001-serial-amba-pl011-add-RS485-support.patch" this change is necesarry otherwise the RTS-line will be pulled up in SER_RS485_RTS_BEFORE_SEND mode before sending data. This hinders the driver to receive data, f.ex. when the device is an RS485 slave device.
>
> Signed-off-by: jmades <jochen@xxxxxxxxx>
Patch is correct, but commit message could be improved:
* Subject should be in imperative mood (by convention), it should be
prepended by "serial: pl011: " (in line with previous commits touching
this driver, use "git log --oneline amba-pl011.c") and the trailing dot
is unnecessary, e.g.:
"serial: pl011: Fix incorrect rs485 RTS polarity on set_mctrl"
* Commit message should be wrapped at 72 characters (so that it appears
centered when displayed with "git log" on an 80 chars terminal).
The reference to "0001-serial-amba-pl011-add-RS485-support.patch"
should be replaced with a reference to the offending commit, e.g.:
"Commit 8d479237727c ("serial: amba-pl011: add RS485 support") sought
to keep RTS deasserted on set_mctrl if rs485 is enabled. However it
did so only if deasserted RTS polarity is high. Fix it in case it's
low."
Feel free to copy this to a v2 of your patch and amend as you see fit.
* Add tags for the offending commit:
Fixes: 8d479237727c ("serial: amba-pl011: add RS485 support")
Cc: stable@xxxxxxxxxxxxxxx # v5.15+
* Be sure to cc the author of the offending commit.
Thanks,
Lukas
> ---
> drivers/tty/serial/amba-pl011.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
> index 537f37ac4..1749c1498 100644
> --- 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);
