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Subject: Re: [PATCH v2 1/2] tty/serial: Add rx-tx-swap OF option to
 stm32-usart
To:     Martin Devera <devik@eaxlabs.cz>, <linux-kernel@vger.kernel.org>
CC:     <devicetree@vger.kernel.org>,
        Alexandre Torgue <alexandre.torgue@st.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Rob Herring <robh+dt@kernel.org>,
        <linux-arm-kernel@lists.infradead.org>,
        Maxime Coquelin <mcoquelin.stm32@gmail.com>,
        <linux-serial@vger.kernel.org>, Jiri Slaby <jirislaby@kernel.org>,
        <linux-stm32@st-md-mailman.stormreply.com>,
        Le Ray <erwan.leray@st.com>
References: <CAL_JsqK8+M=Vg0PiDXP2f1LrEp4hSVea6piAASMGu1H=pxme6Q@mail.gmail.com>
 <20210227164157.30971-1-devik@eaxlabs.cz>
From:   Fabrice Gasnier <fabrice.gasnier@foss.st.com>
Message-ID: <439a0d7a-cc0e-764b-7ed8-668b5a85f4a7@foss.st.com>
Date:   Mon, 1 Mar 2021 11:28:50 +0100
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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@eaxlabs.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)

>  	cr3 = readl_relaxed(port->membase + ofs->cr3);
>  	cr3 &= USART_CR3_TXFTIE | USART_CR3_RXFTCFG_MASK | USART_CR3_RXFTIE
>  		| USART_CR3_TXFTCFG_MASK;
> @@ -1078,6 +1078,7 @@ static struct stm32_port *stm32_usart_of_get_port(struct platform_device *pdev)
>  	stm32_ports[id].hw_flow_control =
>  		of_property_read_bool (np, "st,hw-flow-ctrl") /*deprecated*/ ||
>  		of_property_read_bool (np, "uart-has-rtscts");
> +	stm32_ports[id].swap = of_property_read_bool(np, "rx-tx-swap");

The swap option/bit is available starting with stm32f7 (e.g. not on
stm32f4).

This could be added to compatible data, e.g. as done for other
capabilities in stm32-usart.h. E.g you could add a "has_swap" in struct
stm32_usart_config, then use it at probe time:
	if (cfg->has_swap)
		stm32_ports[id].swap = ...;

Thanks for your patch,
Best regards,
Fabrice

>  	stm32_ports[id].port.line = id;
>  	stm32_ports[id].cr1_irq = USART_CR1_RXNEIE;
>  	stm32_ports[id].cr3_irq = 0;
> diff --git a/drivers/tty/serial/stm32-usart.h b/drivers/tty/serial/stm32-usart.h
> index cb4f327c46db..2f054e2dc0ab 100644
> --- a/drivers/tty/serial/stm32-usart.h
> +++ b/drivers/tty/serial/stm32-usart.h
> @@ -271,6 +271,7 @@ struct stm32_port {
>  	int last_res;
>  	bool tx_dma_busy;	 /* dma tx busy               */
>  	bool hw_flow_control;
> +	bool swap;		 /* swap RX & TX pins */
>  	bool fifoen;
>  	int wakeirq;
>  	int rdr_mask;		/* receive data register mask */
>