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 12:51:28 +0300 (EEST)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     Lino Sanfilippo <LinoSanfilippo@....de>
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 2/9] serial: core, 8250: set RS485 termination gpio
 in serial core

On Sun, 3 Jul 2022, Lino Sanfilippo 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.
> 
> Beside fixing the termination GPIO line setting for the 8250 driver this
> change also makes setting the termination GPIO generic for all UART
> drivers.
> 
> Signed-off-by: Lino Sanfilippo <l.sanfilippo@...bus.com>
> ---
>  drivers/tty/serial/8250/8250_port.c |  3 ---
>  drivers/tty/serial/serial_core.c    | 12 ++++++++++++
>  2 files changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
> index ed2a606f2da7..72252d956f17 100644
> --- a/drivers/tty/serial/8250/8250_port.c
> +++ b/drivers/tty/serial/8250/8250_port.c
> @@ -676,9 +676,6 @@ int serial8250_em485_config(struct uart_port *port, struct ktermios *termios,
>  		rs485->flags &= ~SER_RS485_RTS_AFTER_SEND;
>  	}
>  
> -	gpiod_set_value(port->rs485_term_gpio,
> -			rs485->flags & SER_RS485_TERMINATE_BUS);
> -

I sent a series to make .rs485_supported per uart_port and properly set 
SER_RS485_TERMINATE_BUS according to DT config. With that series added 
first, SER_RS485_TERMINATE_BUS should also be removed from 
serial8250_em485_supported so that serial core can properly manage 
it all.

-- 
 i.