linux-kernel - Re: [PATCH v2 2/9] serial: core, 8250: set RS485 termination gpio in serial core

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Date:   Mon, 4 Jul 2022 11:25:22 +0200
From:   Lino Sanfilippo <LinoSanfilippo@....de>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Vladimir Zapolskiy <vz@...ia.com>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        devicetree <devicetree@...r.kernel.org>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Lukas Wunner <lukas@...ner.de>, p.rosenberger@...bus.com,
        Lino Sanfilippo <l.sanfilippo@...bus.com>
Subject: Re: [PATCH v2 2/9] serial: core, 8250: set RS485 termination gpio in
 serial core



On 03.07.22 20:31, Andy Shevchenko wrote:
> On Sun, Jul 3, 2022 at 7:02 PM Lino Sanfilippo <LinoSanfilippo@....de> wrote:
>>
>> From: Lino Sanfilippo <l.sanfilippo@...bus.com>
>>
>> In serial8250_em485_config() the termination GPIO is set with the uart_port
>> spinlock held. This is an issue if setting the GPIO line can sleep (e.g.
>> since the concerning GPIO expander is connected via SPI or I2C).
>>
>> Fix this by setting the termination line outside of the uart_port spinlock
>> in the serial core and using gpiod_set_value_cansleep() which instead of
>> gpiod_set_value() allows to sleep.
>
> allows it to
>

Ok.

>> Beside fixing the termination GPIO line setting for the 8250 driver this
>> change also makes setting the termination GPIO generic for all UART
>> drivers.
>
> ...
>
>> +static void uart_set_rs485_termination(struct uart_port *port,
>> +                                      const struct serial_rs485 *rs485)
>> +{
>
>> +       if (!port->rs485_term_gpio
>
> This duplicates the check the GPIO library does. Drop it.
>

Ok.

>> || !(rs485->flags & SER_RS485_ENABLED))
>> +               return;
>> +
>> +       gpiod_set_value_cansleep(port->rs485_term_gpio,
>> +                                !!(rs485->flags & SER_RS485_TERMINATE_BUS));
>> +}
>

Thanks for the review!

Regards,
Lino