[PATCH 5.15 112/120] serial: stm32: Use TC interrupt to deassert GPIO RTS in RS485 mode

Greg Kroah-Hartman
2022-12-05T19:40:43Z

From: Marek Vasut <marex@denx.de>

[ Upstream commit d7c76716169ddc37cf6316ff381d34ea807fbfd7 ]

In case the RS485 mode is emulated using GPIO RTS, use the TC interrupt
to deassert the GPIO RTS, otherwise the GPIO RTS stays asserted after a
transmission ended and the RS485 cannot work.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Alexandre Torgue <alexandre.torgue@foss.st.com>
Cc: Erwan Le Ray <erwan.leray@foss.st.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jean Philippe Romain <jean-philippe.romain@foss.st.com>
Cc: Valentin Caron <valentin.caron@foss.st.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-stm32@st-md-mailman.stormreply.com
To: linux-serial@vger.kernel.org
Link: https://lore.kernel.org/r/20220430162845.244655-2-marex@denx.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/tty/serial/stm32-usart.c | 42 ++++++++++++++++++++++++++++++--
drivers/tty/serial/stm32-usart.h | 1 +
2 files changed, 41 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index f2cef5f7ae5a..86f044a96de1 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -314,6 +314,14 @@ static void stm32_usart_tx_interrupt_enable(struct uart_port *port)
stm32_usart_set_bits(port, ofs->cr1, USART_CR1_TXEIE);
}

+static void stm32_usart_tc_interrupt_enable(struct uart_port *port)
+{
+ struct stm32_port *stm32_port = to_stm32_port(port);
+ const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
+
+ stm32_usart_set_bits(port, ofs->cr1, USART_CR1_TCIE);
+}
+
static void stm32_usart_tx_interrupt_disable(struct uart_port *port)
{
struct stm32_port *stm32_port = to_stm32_port(port);
@@ -325,6 +333,14 @@ static void stm32_usart_tx_interrupt_disable(struct uart_port *port)
stm32_usart_clr_bits(port, ofs->cr1, USART_CR1_TXEIE);
}

+static void stm32_usart_tc_interrupt_disable(struct uart_port *port)
+{
+ struct stm32_port *stm32_port = to_stm32_port(port);
+ const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
+
+ stm32_usart_clr_bits(port, ofs->cr1, USART_CR1_TCIE);
+}
+
static void stm32_usart_rs485_rts_enable(struct uart_port *port)
{
struct stm32_port *stm32_port = to_stm32_port(port);
@@ -462,6 +478,13 @@ static void stm32_usart_transmit_chars(struct uart_port *port)
u32 isr;
int ret;

+ if (!stm32_port->hw_flow_control &&
+ port->rs485.flags & SER_RS485_ENABLED) {
+ stm32_port->txdone = false;
+ stm32_usart_tc_interrupt_disable(port);
+ stm32_usart_rs485_rts_enable(port);
+ }
+
if (port->x_char) {
if (stm32_port->tx_dma_busy)
stm32_usart_clr_bits(port, ofs->cr3, USART_CR3_DMAT);
@@ -501,8 +524,14 @@ static void stm32_usart_transmit_chars(struct uart_port *port)
if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS)
uart_write_wakeup(port);

- if (uart_circ_empty(xmit))
+ if (uart_circ_empty(xmit)) {
stm32_usart_tx_interrupt_disable(port);
+ if (!stm32_port->hw_flow_control &&
+ port->rs485.flags & SER_RS485_ENABLED) {
+ stm32_port->txdone = true;
+ stm32_usart_tc_interrupt_enable(port);
+ }
+ }
}

static irqreturn_t stm32_usart_interrupt(int irq, void *ptr)
@@ -515,6 +544,13 @@ static irqreturn_t stm32_usart_interrupt(int irq, void *ptr)

sr = readl_relaxed(port->membase + ofs->isr);

+ if (!stm32_port->hw_flow_control &&
+ port->rs485.flags & SER_RS485_ENABLED &&
+ (sr & USART_SR_TC)) {
+ stm32_usart_tc_interrupt_disable(port);
+ stm32_usart_rs485_rts_disable(port);
+ }
+
if ((sr & USART_SR_RTOF) && ofs->icr != UNDEF_REG)
writel_relaxed(USART_ICR_RTOCF,
port->membase + ofs->icr);
@@ -612,8 +648,10 @@ static void stm32_usart_start_tx(struct uart_port *port)
{
struct circ_buf *xmit = &port->state->xmit;

- if (uart_circ_empty(xmit) && !port->x_char)
+ if (uart_circ_empty(xmit) && !port->x_char) {
+ stm32_usart_rs485_rts_disable(port);
return;
+ }

stm32_usart_rs485_rts_enable(port);

diff --git a/drivers/tty/serial/stm32-usart.h b/drivers/tty/serial/stm32-usart.h
index 07ac291328cd..ad6335155de2 100644
--- a/drivers/tty/serial/stm32-usart.h
+++ b/drivers/tty/serial/stm32-usart.h
@@ -267,6 +267,7 @@ struct stm32_port {
bool hw_flow_control;
bool swap; /* swap RX & TX pins */
bool fifoen;
+ bool txdone;
int rxftcfg; /* RX FIFO threshold CFG */
int txftcfg; /* TX FIFO threshold CFG */
bool wakeup_src;
--
2.35.1