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Subject: Re: [PATCH 2/8] serial: core, 8250: set RS485 termination gpio in
 serial core
To:     =?UTF-8?Q?Ilpo_J=c3=a4rvinen?= <ilpo.jarvinen@linux.intel.com>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jirislaby@kernel.org>, robh+dt@kernel.org,
        krzysztof.kozlowski+dt@linaro.org,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        vz@mleia.com, linux-arm-kernel@lists.infradead.org,
        devicetree@vger.kernel.org,
        linux-serial <linux-serial@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>, lukas@wunner.de,
        p.rosenberger@kunbus.com, Lino Sanfilippo <l.sanfilippo@kunbus.com>
References: <20220622154659.8710-1-LinoSanfilippo@gmx.de>
 <20220622154659.8710-3-LinoSanfilippo@gmx.de>
 <83762813-70ec-93c3-4015-5676ce9534fd@linux.intel.com>
From:   Lino Sanfilippo <LinoSanfilippo@gmx.de>
Message-ID: <aa851698-ff26-a319-500a-575a9c669d95@gmx.de>
Date:   Sun, 26 Jun 2022 17:41:35 +0200
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Hi,

On 25.06.22 at 12:40, Ilpo J=C3=A4rvinen wrote:
>> +
>>  int uart_rs485_config(struct uart_port *port)
>>  {
>>  	struct serial_rs485 *rs485 =3D &port->rs485;
>>  	int ret;
>>
>>  	uart_sanitize_serial_rs485(port, rs485);
>> +	uart_set_rs485_termination(port, rs485);
>>
>>  	ret =3D 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 =3D 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 uar=
t_port to track the
current state?


Regards,
Lino