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

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Message-ID: <CAHp75Vf7Lm9J3GONazY1OZdMLSWp3aa2iQNztsSVZOPWy3=cfA@mail.gmail.com>
Date:   Sun, 3 Jul 2022 20:31:32 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Lino Sanfilippo <LinoSanfilippo@....de>
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 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

> 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.

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

-- 
With Best Regards,
Andy Shevchenko