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:   Wed, 13 Dec 2023 23:31:12 +0100
From:   Lino Sanfilippo <LinoSanfilippo@....de>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        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>,
        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 11.12.23 12:00, Ilpo Järvinen wrote:
> 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.
>

Hmm, ok. What I meant was that the structure is nullified. "set to NULL" is maybe a bit
misleading. I will correct this.

> 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.
>

Yes. BTW: Another "no_rs485" configuration setting can be found in the ar933x driver.
If we do not want to keep those assignments I can remove the one for the imx
driver with the next version of this patch...

>> 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>
>