Hi,
On 02.01.22 at 11:07, Lukas Wunner wrote:
> 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);
Does this logic really have to be implemented in the driver? 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.
Regards,
Lino
