linux-kernel - Re: [PATCH v5 5/7] serial: core, imx: do not set RS485 enabled if it is not supported

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Date:   Mon, 11 Dec 2023 13:00:22 +0200 (EET)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     Lino Sanfilippo <l.sanfilippo@...bus.com>
cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        u.kleine-koenig@...gutronix.de, shawnguo@...nel.org,
        s.hauer@...gutronix.de, mcoquelin.stm32@...il.com,
        alexandre.torgue@...s.st.com, cniedermaier@...electronics.com,
        hugo@...ovil.com, LKML <linux-kernel@...r.kernel.org>,
        linux-serial <linux-serial@...r.kernel.org>,
        LinoSanfilippo@....de, Lukas Wunner <lukas@...ner.de>,
        p.rosenberger@...bus.com, stable@...r.kernel.org
Subject: Re: [PATCH v5 5/7] serial: core, imx: do not set RS485 enabled if
 it is not supported

On Sat, 9 Dec 2023, Lino Sanfilippo wrote:

> If the imx driver cannot support RS485 it sets the ports rs485_supported
> structure to NULL.

No, an embedded struct inside struct uart_port cannot be set to NULL, 
it's always there.

Looking into the code, that setting of rs485_supported from imx_no_rs485 
is actually superfluous as it should be already cleared to zeros on alloc.

> But it still calls uart_get_rs485_mode() which may set
> the RS485_ENABLED flag nevertheless.
> 
> This may lead to an attempt to configure RS485 even if it is not supported
> when the flag is evaluated in uart_configure_port() at port startup.
> 
> Avoid this by bailing out of uart_get_rs485_mode() if the RS485_ENABLED
> flag is not supported by the caller.
> 
> With this fix a check for RTS availability is now obsolete in the imx
> driver, since it can not evaluate to true any more. Remove this check, too.
> 
> Fixes: 00d7a00e2a6f ("serial: imx: Fill in rs485_supported")
> Cc: Shawn Guo <shawnguo@...nel.org>
> Cc: Sascha Hauer <s.hauer@...gutronix.de>
> Cc: stable@...r.kernel.org
> Suggested-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
> Signed-off-by: Lino Sanfilippo <l.sanfilippo@...bus.com>

-- 
 i.