linux-kernel - Re: [PATCH v2 1/9] serial: core: only get RS485 termination GPIO if supported

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Message-ID: <f318294d-2641-5a38-6d9c-ec96f3ec2b5f@gmx.de>
Date:   Mon, 4 Jul 2022 17:07:03 +0200
From:   Lino Sanfilippo <LinoSanfilippo@....de>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        vz@...ia.com, linux-arm-kernel@...ts.infradead.org,
        devicetree@...r.kernel.org,
        linux-serial <linux-serial@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Lukas Wunner <lukas@...ner.de>, p.rosenberger@...bus.com,
        Lino Sanfilippo <l.sanfilippo@...bus.com>
Subject: Re: [PATCH v2 1/9] serial: core: only get RS485 termination GPIO if
 supported



On 04.07.22 11:55, Ilpo Järvinen wrote:
> On Sun, 3 Jul 2022, Lino Sanfilippo wrote:
>
>> From: Lino Sanfilippo <l.sanfilippo@...bus.com>
>>
>> In uart_get_rs485_mode() only try to get a termination GPIO if RS485 bus
>> termination is supported by the driver. This prevents from allocating
>> and holding a GPIO descriptor for the drivers lifetimg that will never be
>> used.
>>
>> Signed-off-by: Lino Sanfilippo <l.sanfilippo@...bus.com>
>> ---
>>
>> NOTE:
>> This patch follows the design decision that "rs485_supported" is
>> set by the driver at initialization and cannot be modified
>> afterwards. However the better approach would be to let the serial
>> core modify the termination GPIO support setting based on the
>> existence of a termination GPIO. If "rs485_supported" is not a
>> read-only value any more in future the logic implemented in this
>> patch should be adjusted accordingly.
>>
>>  drivers/tty/serial/serial_core.c | 10 ++++++++++
>>  1 file changed, 10 insertions(+)
>>
>> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
>> index 85ef7ef00b82..3768663dfa4d 100644
>> --- a/drivers/tty/serial/serial_core.c
>> +++ b/drivers/tty/serial/serial_core.c
>> @@ -3404,6 +3404,16 @@ int uart_get_rs485_mode(struct uart_port *port)
>>  	 */
>>  	port->rs485_term_gpio = devm_gpiod_get_optional(dev, "rs485-term",
>>  							GPIOD_OUT_LOW);
>> +
>> +	if (port->rs485_term_gpio &&
>> +	    !(port->rs485_supported->flags & SER_RS485_TERMINATE_BUS)) {
>> +		dev_warn(port->dev,
>> +			"%s (%d): RS485 termination gpio not supported by driver\n",
>> +			port->name, port->line);
>> +		devm_gpiod_put(dev, port->rs485_term_gpio);
>> +		port->rs485_term_gpio = NULL;
>> +	}
>> +
>>  	if (IS_ERR(port->rs485_term_gpio)) {
>>  		ret = PTR_ERR(port->rs485_term_gpio);
>>  		port->rs485_term_gpio = NULL;
>
> I sent a series to embed supported_rs485 to uart_port and manage
> SER_RS485_TERMINATE_BUS properly so I think this won't be necessary
> with that?
>
>

This is why I wrote the "NOTE" above. But yes, this patch is not needed
any more. I will drop it in the next version.


Regards,
Lino