[PATCH v7 2/2] tty/serial: Add rx-tx-swap OF option to stm32-usart

[Martin Devera <devik@eaxlabs.cz>]

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>
Acked-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>
---
v6: 
  - add version changelog
v4:
  - delete superfluous has_swap=false
v3:
  - add has_swap to stm32_usart_info (because F4 line
    doesn't support swapping)
  - move swap variable init from stm32_usart_of_get_port
    to stm32_usart_init_port because info struct is not
    initialized in stm32_usart_of_get_port yet
  - set USART_CR2_SWAP in stm32_usart_startup too
v2:
  - change st,swap to rx-tx-swap (pointed out by Rob Herring)
  - rebase patches as suggested by Greg Kroah-Hartman
---
 drivers/tty/serial/stm32-usart.c | 11 ++++++++++-
 drivers/tty/serial/stm32-usart.h |  4 ++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index b3675cf25a69..d390f7da1441 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -644,6 +644,12 @@ 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)
 		stm32_usart_set_bits(port, ofs->rqr, USART_RQR_RXFRQ);
@@ -758,7 +764,7 @@ 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;
 	cr3 = readl_relaxed(port->membase + ofs->cr3);
 	cr3 &= USART_CR3_TXFTIE | USART_CR3_RXFTCFG_MASK | USART_CR3_RXFTIE
 		| USART_CR3_TXFTCFG_MASK;
@@ -1006,6 +1012,9 @@ static int stm32_usart_init_port(struct stm32_port *stm32port,
 			return stm32port->wakeirq ? : -ENODEV;
 	}
 
+	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);
diff --git a/drivers/tty/serial/stm32-usart.h b/drivers/tty/serial/stm32-usart.h
index cb4f327c46db..a85391e71e8e 100644
--- a/drivers/tty/serial/stm32-usart.h
+++ b/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,
@@ -271,6 +274,7 @@ 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 */
-- 
2.11.0