Re: [PATCH 2/8] serial: core, 8250: set RS485 termination gpio in serial core

[Lino Sanfilippo]

Hi,

On 25.06.22 at 12:40, Ilpo Järvinen wrote:
>> +
>>  int uart_rs485_config(struct uart_port *port)
>>  {
>>  	struct serial_rs485 *rs485 = &port->rs485;
>>  	int ret;
>>
>>  	uart_sanitize_serial_rs485(port, rs485);
>> +	uart_set_rs485_termination(port, rs485);
>>
>>  	ret = port->rs485_config(port, rs485);
>>  	if (ret)
>> @@ -1400,6 +1411,7 @@ static int uart_set_rs485_config(struct uart_port *port,
>>  	if (ret)
>>  		return ret;
>>  	uart_sanitize_serial_rs485(port, &rs485);
>> +	uart_set_rs485_termination(port, &rs485);
>>
>>  	spin_lock_irqsave(&port->lock, flags);
>>  	ret = port->rs485_config(port, &rs485);
>
> When port->rs485_config(port, &rs485) returns non-zero, the input got
> partially applied?
>
>
The thing is we dont know what the state of the termination GPIO (asserted or deasserted)
was before we set it and port->rs485_config() failed, so we cannot restore it.
We could read the GPIO before we change it but AFAIK this is unsafe since it is an output
pin. Maybe add a boolean variable "rs485_termination_gpio_asserted" to uart_port to track the
current state?


Regards,
Lino