linux-kernel - Re: [PATCH 4/8] serial: core: sanitize RS485 delays read from device tree

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Date:   Sat, 25 Jun 2022 13:05:03 +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@...ner.de,
        p.rosenberger@...bus.com, Lino Sanfilippo <l.sanfilippo@...bus.com>
Subject: Re: [PATCH 4/8] serial: core: sanitize RS485 delays read from device
 tree

On Wed, 22 Jun 2022, Lino Sanfilippo wrote:

> From: Lino Sanfilippo <l.sanfilippo@...bus.com>
> 
> When setting the RS485 configuration from userspace via TIOCSRS485 the
> delays are clamped to 100ms. Make this consistent with the values passed
> in by means of device tree parameters.
> 
> Signed-off-by: Lino Sanfilippo <l.sanfilippo@...bus.com>
> ---
>  drivers/tty/serial/serial_core.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
> index fa6acadd7d0c..2e9f90e73e62 100644
> --- a/drivers/tty/serial/serial_core.c
> +++ b/drivers/tty/serial/serial_core.c
> @@ -3382,6 +3382,8 @@ int uart_get_rs485_mode(struct uart_port *port)
>  		rs485conf->delay_rts_after_send = 0;
>  	}
>  
> +	uart_sanitize_serial_rs485_delays(port, rs485conf);
> +
>  	/*
>  	 * Clear full-duplex and enabled flags, set RTS polarity to active high
>  	 * to get to a defined state with the following properties:
> -- 
> 2.36.1

While above works, if we go to this change user-visible behavior route, 
uart_get_rs485_mode() could just call full uart_sanitize_serial_rs485()?

The sanitization is currently being done during probe in 
uart_rs485_config() which has another challenge to tackle. The RS485 
supporting UART drivers are not consistently calling it during their 
probe(), only a few of them do but it would make more sense if all of them 
would enter into RS485 mode w/  linux,rs485-enabled-at-boot-time being 
set. However, making such change might run afoul with the expectations of 
users.


-- 
 i.