linux-kernel - Re: [PATCH v2 1/2] tty/serial: Add rx-tx-swap OF option to stm32-usart

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Date:   Mon, 1 Mar 2021 23:40:26 +0100
From:   Martin DEVERA <devik@...labs.cz>
To:     Fabrice Gasnier <fabrice.gasnier@...s.st.com>,
        linux-kernel@...r.kernel.org
Cc:     devicetree@...r.kernel.org,
        Alexandre Torgue <alexandre.torgue@...com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        linux-serial@...r.kernel.org, Jiri Slaby <jirislaby@...nel.org>,
        linux-stm32@...md-mailman.stormreply.com,
        Le Ray <erwan.leray@...com>
Subject: Re: [PATCH v2 1/2] tty/serial: Add rx-tx-swap OF option to
 stm32-usart

On 3/1/21 11:28 AM, Fabrice Gasnier wrote:
> On 2/27/21 5:41 PM, Martin Devera wrote:
>> STM32 F7/H7 usarts supports RX & TX pin swapping.
>> Add option to turn it on.
>> Tested on STM32MP157.
>>
>> Signed-off-by: Martin Devera <devik@...labs.cz>
>> ---
>>   drivers/tty/serial/stm32-usart.c | 3 ++-
>>   drivers/tty/serial/stm32-usart.h | 1 +
>>   2 files changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
>> index b3675cf25a69..3650c8798061 100644
>> --- a/drivers/tty/serial/stm32-usart.c
>> +++ b/drivers/tty/serial/stm32-usart.c
>> @@ -758,7 +758,7 @@ static void stm32_usart_set_termios(struct uart_port *port,
>>   	cr1 = USART_CR1_TE | USART_CR1_RE;
>>   	if (stm32_port->fifoen)
>>   		cr1 |= USART_CR1_FIFOEN;
>> -	cr2 = 0;
>> +	cr2 = stm32_port->swap ? USART_CR2_SWAP : 0;
> Hi Martin,
>
> Same could be done in the startup routine, that enables the port for
> reception (as described in Documentation/driver-api/serial/driver.rst)
Hello Fabrice,

I already incorporated all your comments but I'm struggling with the one 
above.
The code must be in stm32_usart_set_termios too, because CR2 is modified.
What is the reason to have it in startup() ?
Is it because USART can be started without calling set_termios at all ? Like
to reuse bootloader's last settings ?

Thanks, Martin