linux-kernel - Re: [PATCH] tty: atmel_serial: use the correct RTS flag.

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Message-ID: <20240813-absinthe-plaza-70575e847015@thorsis.com>
Date: Tue, 13 Aug 2024 09:59:51 +0200
From: Alexander Dahl <ada@...rsis.com>
To: Mathieu Othacehe <othacehe@....org>
Cc: Richard Genoud <richard.genoud@...tlin.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jirislaby@...nel.org>,
	Nicolas Ferre <nicolas.ferre@...rochip.com>,
	Alexandre Belloni <alexandre.belloni@...tlin.com>,
	Claudiu Beznea <claudiu.beznea@...on.dev>,
	linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Subject: Re: [PATCH] tty: atmel_serial: use the correct RTS flag.

Hello Mathieu,

Am Thu, Aug 08, 2024 at 08:06:37AM +0200 schrieb Mathieu Othacehe:
> In RS485 mode, the RTS pin is driven high by hardware when the transmitter
> is operating. This behaviour cannot be changed. This means that the driver
> should claim that it supports SER_RS485_RTS_ON_SEND and not
> SER_RS485_RTS_AFTER_SEND.
> 
> Otherwise, when configuring the port with the SER_RS485_RTS_ON_SEND, one
> get the following warning:
> 
> kern.warning kernel: atmel_usart_serial atmel_usart_serial.2.auto:
> ttyS1 (1): invalid RTS setting, using RTS_AFTER_SEND instead

I've seen this warning already, when migrating a sam9x60 based board
from LTS kernel 6.1 to 6.6, so thanks for taking care of this.

I can confirm after applying the patch on top of 6.6.44 the warning is
gone, and RS-485 communication still works on our platform, so …

Tested-by: Alexander Dahl <ada@...rsis.com>

Does this deserve a Fixes tag for the change which introduced struct
serial_rs485 to the atmel serial driver?  Then it should be this:

Fixes: af47c491e3c7 ("serial: atmel: Fill in rs485_supported")

Greets
Alex

> which is contradictory with what's really happening.
> 
> Signed-off-by: Mathieu Othacehe <othacehe@....org>
> ---
>  drivers/tty/serial/atmel_serial.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
> index 0a90964d6d107..09b246c9e389e 100644
> --- a/drivers/tty/serial/atmel_serial.c
> +++ b/drivers/tty/serial/atmel_serial.c
> @@ -2514,7 +2514,7 @@ static const struct uart_ops atmel_pops = {
>  };
>  
>  static const struct serial_rs485 atmel_rs485_supported = {
> -	.flags = SER_RS485_ENABLED | SER_RS485_RTS_AFTER_SEND | SER_RS485_RX_DURING_TX,
> +	.flags = SER_RS485_ENABLED | SER_RS485_RTS_ON_SEND | SER_RS485_RX_DURING_TX,
>  	.delay_rts_before_send = 1,
>  	.delay_rts_after_send = 1,
>  };
> -- 
> 2.45.2
> 
>