linux-kernel - Re: [PATCH 1/1] drivers: tty: imx: fix flags of rs485 not work properly

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Message-ID: <f09c546e-4f0c-81a0-8acf-24f4e5d29229@linux.intel.com>
Date: Fri, 20 Sep 2024 18:58:21 +0300 (EEST)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: Jiri Slaby <jslaby@...e.cz>, LiangCheng Wang <zaq14760@...il.com>
cc: shawnguo@...nel.org, s.hauer@...gutronix.de, 
    Greg Kroah-Hartman <gregkh@...uxfoundation.org>, kernel@...gutronix.de, 
    festevam@...il.com, u.kleine-koenig@...gutronix.de, 
    cniedermaier@...electronics.com, l.sanfilippo@...bus.com, 
    linux@...musvillemoes.dk, stefan.eichenberger@...adex.com, 
    tglx@...utronix.de, rickaran@...s.com, LKML <linux-kernel@...r.kernel.org>, 
    linux-serial <linux-serial@...r.kernel.org>, imx@...ts.linux.dev, 
    linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/1] drivers: tty: imx: fix flags of rs485 not work
 properly

On Fri, 6 Sep 2024, Jiri Slaby wrote:

> It seems gmail refuses to send this to zaq14760@...il.com (the author).
> 
> On 06. 09. 24, 4:19, LiangCheng Wang wrote:
> > The rs485.flags are lost in functions such as imx_uart_stop_tx(),
> > causing the function of RS485 to be invalid when using the
> > serial port as the RS485 port. Use a variable to store the state to
> > avoid this issue.
> 
> AFAICT, this feels rather wrong. Any rs485 experts around?

It is wrong. The patch makes no sense at all and prevents 
reconfiguring/setting rs485 from userspace.

> At minimum, how are the flags "lost" and why this does not matter to other
> drivers?

Perhaps some userspace program is altering rs485 settings, definitely 
nothing in imx_uart_stop_tx() writes to it. I'm skeptical it would be a 
problem in the kernel, especially given the patch that is supposed to 
"avoid the issue" (whatever the issue is).

> > --- a/drivers/tty/serial/imx.c
> > +++ b/drivers/tty/serial/imx.c
> > @@ -209,7 +209,7 @@ struct imx_port {
> >   	const struct imx_uart_data *devdata;
> >     	struct mctrl_gpios *gpios;
> > -
> > +	int flags;
> 
> Definitely not int for flags.

Driver is not supposed to duplicate the rs485 flags at all.

-- 
 i.