linux-kernel - Re: [PATCH v7 1/3] serial: sc16is7xx: announce support of SER_RS485_RTS_ON

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Message-Id: <20240423145910.c3141dbd01665213526b54fa@hugovil.com>
Date: Tue, 23 Apr 2024 14:59:10 -0400
From: Hugo Villeneuve <hugo@...ovil.com>
To: Konstantin Pugin <ria.freelander@...il.com>
Cc: krzk@...nel.org, conor@...nel.org, lkp@...el.com, vz@...ia.com,
 robh@...nel.org, jcmvbkbc@...il.com, nicolas.ferre@...rochip.com,
 manikanta.guntupalli@....com, corbet@....net, ychuang3@...oton.com,
 u.kleine-koenig@...gutronix.de, Maarten.Brock@...ls.nl, Greg Kroah-Hartman
 <gregkh@...uxfoundation.org>, Jiri Slaby <jirislaby@...nel.org>, Hugo
 Villeneuve <hvilleneuve@...onoff.com>, Andy Shevchenko <andy@...nel.org>,
 Lech Perczak <lech.perczak@...lingroup.com>, Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
 linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org
Subject: Re: [PATCH v7 1/3] serial: sc16is7xx: announce support of
 SER_RS485_RTS_ON_SEND

On Mon, 22 Apr 2024 16:32:13 +0300
Konstantin Pugin <ria.freelander@...il.com> wrote:

Hi Konstantin,

> The hardware supports both RTS_ON_SEND and RTS_AFTER_SEND modes, but
> after the commit 4afeced55baa ("serial: core: fix sanitizing check for
> RTS settings") we always end up with SER_RS485_RTS_AFTER_SEND set and
> always write to the register field SC16IS7XX_EFCR_RTS_INVERT_BIT, which
> breaks some hardware using these chips.

it took me a long time to properly understand what you meant in your
commit message. In my setup, I have the property rs485-rts-active-low
defined, and couldn't reproduce the problem. It is only after I
commented this property that I got a warning about the "invalid RTS
setting"... I also got it by defining rs485-rts-active-high.

I suggest the following changes to the commit message:

----
When specifying flag SER_RS485_RTS_ON_SEND in RS485 configuration,
we get the following warning after commit 4afeced55baa ("serial: core:
fix sanitizing check for RTS settings"):

    invalid RTS setting, using RTS_AFTER_SEND instead

This results in SER_RS485_RTS_AFTER_SEND being set and the
driver always write to the register field SC16IS7XX_EFCR_RTS_INVERT_BIT,
which breaks some hardware using these chips.

The hardware supports both RTS_ON_SEND and RTS_AFTER_SEND modes, so fix
this by announcing support for RTS_ON_SEND.
---

If you agree to these changes, feel free to add:

Tested-by: Hugo Villeneuve <hvilleneuve@...onoff.com>

Hugo.


> 
> Fixes: 267913ecf737 ("serial: sc16is7xx: Fill in rs485_supported")
> Signed-off-by: Konstantin Pugin <ria.freelander@...il.com>
> ---
>  drivers/tty/serial/sc16is7xx.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
> index 03cf30e20b75..dfcc804f558f 100644
> --- a/drivers/tty/serial/sc16is7xx.c
> +++ b/drivers/tty/serial/sc16is7xx.c
> @@ -1449,7 +1449,7 @@ static int sc16is7xx_setup_mctrl_ports(struct sc16is7xx_port *s,
>  }
>  
>  static const struct serial_rs485 sc16is7xx_rs485_supported = {
> -	.flags = SER_RS485_ENABLED | SER_RS485_RTS_AFTER_SEND,
> +	.flags = SER_RS485_ENABLED | SER_RS485_RTS_ON_SEND | SER_RS485_RTS_AFTER_SEND,
>  	.delay_rts_before_send = 1,
>  	.delay_rts_after_send = 1,	/* Not supported but keep returning -EINVAL */
>  };
> -- 
> 2.34.1
> 
> 
> 


-- 
Hugo Villeneuve