Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <f318294d-2641-5a38-6d9c-ec96f3ec2b5f@gmx.de>
Date:   Mon, 4 Jul 2022 17:07:03 +0200
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.9.1
Subject: Re: [PATCH v2 1/9] serial: core: only get RS485 termination GPIO if
 supported
Content-Language: en-US
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 <lukas@wunner.de>, p.rosenberger@kunbus.com,
        Lino Sanfilippo <l.sanfilippo@kunbus.com>
References: <20220703170039.2058202-1-LinoSanfilippo@gmx.de>
 <20220703170039.2058202-2-LinoSanfilippo@gmx.de>
 <9bc128a9-7ce3-d1e-dad6-ca91a5564ea8@linux.intel.com>
From:   Lino Sanfilippo <LinoSanfilippo@gmx.de>
In-Reply-To: <9bc128a9-7ce3-d1e-dad6-ca91a5564ea8@linux.intel.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: quoted-printable
Precedence: bulk


On 04.07.22 11:55, Ilpo J=C3=A4rvinen wrote:
> On Sun, 3 Jul 2022, Lino Sanfilippo wrote:
>
>> From: Lino Sanfilippo <l.sanfilippo@kunbus.com>
>>
>> In uart_get_rs485_mode() only try to get a termination GPIO if RS485 bu=
s
>> 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@kunbus.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/seri=
al_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 =3D 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 =3D NULL;
>> +	}
>> +
>>  	if (IS_ERR(port->rs485_term_gpio)) {
>>  		ret =3D PTR_ERR(port->rs485_term_gpio);
>>  		port->rs485_term_gpio =3D 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