tty/serial: Add rx-tx-swap OF option to stm32-usart

STM32 F7/H7 usarts supports RX & TX pin swapping.
Add option to turn it on.
Tested on STM32MP157.
Acked-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>
Signed-off-by: Martin Devera <devik@eaxlabs.cz>
Link: https://lore.kernel.org/r/20210328154306.22674-2-devik@eaxlabs.czSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/stm32-usart.c

@@ -671,6 +671,12 @@ static int stm32_usart_startup(struct uart_port *port)
 	if (ret)
 		return ret;
 
+	if (stm32_port->swap) {
+		val = readl_relaxed(port->membase + ofs->cr2);
+		val |= USART_CR2_SWAP;
+		writel_relaxed(val, port->membase + ofs->cr2);
+	}
+
 	/* RX FIFO Flush */
 	if (ofs->rqr != UNDEF_REG)
 		writel_relaxed(USART_RQR_RXFRQ, port->membase + ofs->rqr);
@@ -789,7 +795,7 @@ 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;
 
 	/* Tx and RX FIFO configuration */
 	cr3 = readl_relaxed(port->membase + ofs->cr3);
@@ -1047,6 +1053,9 @@ static int stm32_usart_init_port(struct stm32_port *stm32port,
 	stm32port->wakeup_src = stm32port->info->cfg.has_wakeup &&
 		of_property_read_bool(pdev->dev.of_node, "wakeup-source");
 
+	stm32port->swap = stm32port->info->cfg.has_swap &&
+		of_property_read_bool(pdev->dev.of_node, "rx-tx-swap");
+
 	stm32port->fifoen = stm32port->info->cfg.has_fifo;
 
 	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);

drivers/tty/serial/stm32-usart.h

@@ -25,6 +25,7 @@ struct stm32_usart_offsets {
 struct stm32_usart_config {
 	u8 uart_enable_bit; /* USART_CR1_UE */
 	bool has_7bits_data;
+	bool has_swap;
 	bool has_wakeup;
 	bool has_fifo;
 	int fifosize;
@@ -76,6 +77,7 @@ struct stm32_usart_info stm32f7_info = {
 	.cfg = {
 		.uart_enable_bit = 0,
 		.has_7bits_data = true,
+		.has_swap = true,
 		.fifosize = 1,
 	}
 };
@@ -97,6 +99,7 @@ struct stm32_usart_info stm32h7_info = {
 	.cfg = {
 		.uart_enable_bit = 0,
 		.has_7bits_data = true,
+		.has_swap = true,
 		.has_wakeup = true,
 		.has_fifo = true,
 		.fifosize = 16,
@@ -268,6 +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;
 	bool wakeup_src;
 	int rdr_mask;		/* receive data register mask */