linux-kernel - Re: [PATCH 4/8] serial: core: sanitize RS485 delays read from device tree

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Date:   Sun, 26 Jun 2022 16:25:03 +0200
From:   Lino Sanfilippo <LinoSanfilippo@....de>
To:     Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        vz@...ia.com, linux-arm-kernel@...ts.infradead.org,
        devicetree@...r.kernel.org,
        linux-serial <linux-serial@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, lukas@...ner.de,
        p.rosenberger@...bus.com, Lino Sanfilippo <l.sanfilippo@...bus.com>
Subject: Re: [PATCH 4/8] serial: core: sanitize RS485 delays read from device
 tree

On 25.06.22 at 12:05, Ilpo Järvinen wrote:
> On Wed, 22 Jun 2022, Lino Sanfilippo wrote:
>
>> From: Lino Sanfilippo <l.sanfilippo@...bus.com>
>>
>> When setting the RS485 configuration from userspace via TIOCSRS485 the
>> delays are clamped to 100ms. Make this consistent with the values passed
>> in by means of device tree parameters.
>>
>> Signed-off-by: Lino Sanfilippo <l.sanfilippo@...bus.com>
>> ---
>>  drivers/tty/serial/serial_core.c | 2 ++
>>  1 file changed, 2 insertions(+)
>>
>> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
>> index fa6acadd7d0c..2e9f90e73e62 100644
>> --- a/drivers/tty/serial/serial_core.c
>> +++ b/drivers/tty/serial/serial_core.c
>> @@ -3382,6 +3382,8 @@ int uart_get_rs485_mode(struct uart_port *port)
>>  		rs485conf->delay_rts_after_send = 0;
>>  	}
>>
>> +	uart_sanitize_serial_rs485_delays(port, rs485conf);
>> +
>>  	/*
>>  	 * Clear full-duplex and enabled flags, set RTS polarity to active high
>>  	 * to get to a defined state with the following properties:
>> --
>> 2.36.1
>
> While above works, if we go to this change user-visible behavior route,
> uart_get_rs485_mode() could just call full uart_sanitize_serial_rs485()?

As it is now uart_sanitize_serial_rs485() will clear the entire serial_rs485 struct and
return immediately if rs485-enabled-at-boot-time (and thus SER_RS485_ENABLED)
is not set. That was one of the reasons I moved the delay checks into an own fucntion. The other
reason is that the remaining sanity check for RTS on send/after send in uart_sanitize_serial_rs485() is not
required in uart_get_rs485_mode() since here we already ensure a sane setting.

Regards,
Lino