[PATCH] serial: ar933x: Add polling support

[PATCH] serial: ar933x: Add polling support

[Sven Eckelmann]

KGDB requires at least the polling hooks .poll_get_char and .poll_put_char
to transmit/receive character via the serial driver.

Signed-off-by: Sven Eckelmann <se@simonwunderlich.de>
---
 drivers/tty/serial/ar933x_uart.c | 62 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 62 insertions(+)

diff --git a/drivers/tty/serial/ar933x_uart.c b/drivers/tty/serial/ar933x_uart.c
index 8bb33556b31208a1707ca7a48db0aa2ca81452bd..5b491db9d2fc01e051f629f224024ac4dc4d35ff 100644
--- a/drivers/tty/serial/ar933x_uart.c
+++ b/drivers/tty/serial/ar933x_uart.c
@@ -560,6 +560,64 @@ static int ar933x_uart_verify_port(struct uart_port *port,
 	return 0;
 }
 
+#ifdef CONFIG_CONSOLE_POLL
+static int ar933x_poll_get_char(struct uart_port *port)
+{
+	struct ar933x_uart_port *up =
+		container_of(port, struct ar933x_uart_port, port);
+	unsigned int rdata;
+	unsigned char ch;
+	u32 imr;
+
+	/* Disable all interrupts */
+	imr = ar933x_uart_read(up, AR933X_UART_INT_EN_REG);
+	ar933x_uart_write(up, AR933X_UART_INT_EN_REG, 0);
+
+	rdata = ar933x_uart_read(up, AR933X_UART_DATA_REG);
+	if ((rdata & AR933X_UART_DATA_RX_CSR) == 0) {
+		/* Enable interrupts */
+		ar933x_uart_write(up, AR933X_UART_INT_EN_REG, imr);
+		return NO_POLL_CHAR;
+	}
+
+	/* remove the character from the FIFO */
+	ar933x_uart_write(up, AR933X_UART_DATA_REG,
+			  AR933X_UART_DATA_RX_CSR);
+
+	ch = rdata & AR933X_UART_DATA_TX_RX_MASK;
+
+	/* Enable interrupts */
+	ar933x_uart_write(up, AR933X_UART_INT_EN_REG, imr);
+
+	return ch;
+}
+
+static void ar933x_poll_put_char(struct uart_port *port, unsigned char c)
+{
+	struct ar933x_uart_port *up =
+		container_of(port, struct ar933x_uart_port, port);
+	u32 imr;
+
+	/* Disable all interrupts */
+	imr = ar933x_uart_read(up, AR933X_UART_INT_EN_REG);
+	ar933x_uart_write(up, AR933X_UART_INT_EN_REG, 0);
+
+	/* Wait until FIFO is empty */
+	while (!(ar933x_uart_read(up, AR933X_UART_DATA_REG) & AR933X_UART_DATA_TX_CSR))
+		cpu_relax();
+
+	/* Write a character */
+	ar933x_uart_putc(up, c);
+
+	/* Wait until FIFO is empty */
+	while (!(ar933x_uart_read(up, AR933X_UART_DATA_REG) & AR933X_UART_DATA_TX_CSR))
+		cpu_relax();
+
+	/* Enable interrupts */
+	ar933x_uart_write(up, AR933X_UART_INT_EN_REG, imr);
+}
+#endif
+
 static const struct uart_ops ar933x_uart_ops = {
 	.tx_empty	= ar933x_uart_tx_empty,
 	.set_mctrl	= ar933x_uart_set_mctrl,
@@ -576,6 +634,10 @@ static const struct uart_ops ar933x_uart_ops = {
 	.request_port	= ar933x_uart_request_port,
 	.config_port	= ar933x_uart_config_port,
 	.verify_port	= ar933x_uart_verify_port,
+#ifdef CONFIG_CONSOLE_POLL
+	.poll_get_char	= ar933x_poll_get_char,
+	.poll_put_char	= ar933x_poll_put_char,
+#endif
 };
 
 static int ar933x_config_rs485(struct uart_port *port, struct ktermios *termios,

---
base-commit: f83ec76bf285bea5727f478a68b894f5543ca76e
change-id: 20251001-ar933x-kgdb-support-25f5451b2a59

Best regards,
-- 
Sven Eckelmann <se@simonwunderlich.de>

Re: [PATCH] serial: ar933x: Add polling support

[Sven Eckelmann]

[-- Attachment #1.1: Type: text/plain, Size: 1059 bytes --]

On Wednesday, 1 October 2025 13:47:26 CEST Sven Eckelmann wrote:
> KGDB requires at least the polling hooks .poll_get_char and .poll_put_char
> to transmit/receive character via the serial driver.
> 
> Signed-off-by: Sven Eckelmann <se@simonwunderlich.de>
> ---
>  drivers/tty/serial/ar933x_uart.c | 62 ++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 62 insertions(+)

I also had a look at break detection to ease the debugging on our side. Just 
to be able to switch to KGDB mode via gdb.

While I got it working, it is more a hack than a good implementation. I've 
attached the hack in case someone wants to continue to work on it.


On Wednesday, 1 October 2025 14:05:41 CEST Greg Kroah-Hartman wrote:
> Right now, the development tree you have sent a patch for is "closed"
> due to the timing of the merge window.  Don't worry, the patch(es) you
> have sent are not lost, and will be looked at after the merge window is
> over (after the -rc1 kernel is released by Linus).

*looks at the calendar* Oh, yes, there was something.

Regards,
	Sven

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From 7892ef568d7ca4c1c2a0ed9fb8edbadfe8e70177 Mon Sep 17 00:00:00 2001
From: Sven Eckelmann <se@simonwunderlich.de>
Date: Mon, 15 Sep 2025 15:35:14 +0200
Subject: [PATCH RFC] serial: ar933x: Handle break events

Signed-off-by: Sven Eckelmann <se@simonwunderlich.de>
---
 drivers/tty/serial/ar933x_uart.c | 53 ++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)

diff --git a/drivers/tty/serial/ar933x_uart.c b/drivers/tty/serial/ar933x_uart.c
index 5b491db9d2fc..bc0a63e4934b 100644
--- a/drivers/tty/serial/ar933x_uart.c
+++ b/drivers/tty/serial/ar933x_uart.c
@@ -105,6 +105,30 @@ static inline void ar933x_uart_stop_tx_interrupt(struct ar933x_uart_port *up)
 	ar933x_uart_write(up, AR933X_UART_INT_EN_REG, up->ier);
 }
 
+static inline void ar933x_uart_start_rxbreak_on_interrupt(struct ar933x_uart_port *up)
+{
+	up->ier |= AR933X_UART_INT_RX_BREAK_ON;
+	ar933x_uart_write(up, AR933X_UART_INT_EN_REG, up->ier);
+}
+
+static inline void ar933x_uart_stop_rxbreak_on_interrupt(struct ar933x_uart_port *up)
+{
+	up->ier &= ~AR933X_UART_INT_RX_BREAK_ON;
+	ar933x_uart_write(up, AR933X_UART_INT_EN_REG, up->ier);
+}
+
+static inline void ar933x_uart_start_rxbreak_off_interrupt(struct ar933x_uart_port *up)
+{
+	up->ier |= AR933X_UART_INT_RX_BREAK_OFF;
+	ar933x_uart_write(up, AR933X_UART_INT_EN_REG, up->ier);
+}
+
+static inline void ar933x_uart_stop_rxbreak_off_interrupt(struct ar933x_uart_port *up)
+{
+	up->ier &= ~AR933X_UART_INT_RX_BREAK_OFF;
+	ar933x_uart_write(up, AR933X_UART_INT_EN_REG, up->ier);
+}
+
 static inline void ar933x_uart_start_rx_interrupt(struct ar933x_uart_port *up)
 {
 	up->ier |= AR933X_UART_INT_RX_VALID;
@@ -212,6 +236,7 @@ static void ar933x_uart_stop_rx(struct uart_port *port)
 		container_of(port, struct ar933x_uart_port, port);
 
 	ar933x_uart_stop_rx_interrupt(up);
+	ar933x_uart_stop_rxbreak_on_interrupt(up);
 }
 
 static void ar933x_uart_break_ctl(struct uart_port *port, int break_state)
@@ -444,11 +469,14 @@ static irqreturn_t ar933x_uart_interrupt(int irq, void *dev_id)
 {
 	struct ar933x_uart_port *up = dev_id;
 	unsigned int status;
+	bool is_break;
 
 	status = ar933x_uart_read(up, AR933X_UART_CS_REG);
 	if ((status & AR933X_UART_CS_HOST_INT) == 0)
 		return IRQ_NONE;
 
+	is_break = status & AR933X_UART_CS_RX_BREAK;
+
 	uart_port_lock(&up->port);
 
 	status = ar933x_uart_read(up, AR933X_UART_INT_REG);
@@ -467,6 +495,29 @@ static irqreturn_t ar933x_uart_interrupt(int irq, void *dev_id)
 		ar933x_uart_tx_chars(up);
 	}
 
+	if (status & AR933X_UART_INT_RX_BREAK_ON)
+		ar933x_uart_write(up, AR933X_UART_INT_REG,
+				  AR933X_UART_INT_RX_BREAK_ON);
+
+	if (status & AR933X_UART_INT_RX_BREAK_OFF)
+		ar933x_uart_write(up, AR933X_UART_INT_REG,
+				  AR933X_UART_INT_RX_BREAK_OFF);
+
+	if (is_break) {
+		/* disable "active break" interrupt */
+		ar933x_uart_stop_rxbreak_on_interrupt(up);
+		ar933x_uart_start_rxbreak_off_interrupt(up);
+
+		/* inform serial core about break */
+		up->port.icount.brk++;
+		if (!up->port.sysrq)
+			uart_handle_break(&up->port);
+	} else if (!(up->ier & AR933X_UART_INT_RX_BREAK_ON)) {
+		/* enable "active break" interrupt */
+		ar933x_uart_start_rxbreak_on_interrupt(up);
+		ar933x_uart_stop_rxbreak_off_interrupt(up);
+	}
+
 	uart_unlock_and_check_sysrq(&up->port);
 
 	return IRQ_HANDLED;
@@ -496,6 +547,7 @@ static int ar933x_uart_startup(struct uart_port *port)
 
 	/* Enable RX interrupts */
 	ar933x_uart_start_rx_interrupt(up);
+	ar933x_uart_start_rxbreak_on_interrupt(up);
 
 	uart_port_unlock_irqrestore(&up->port, flags);
 
@@ -829,6 +881,7 @@ static int ar933x_uart_probe(struct platform_device *pdev)
 	port->ops = &ar933x_uart_ops;
 	port->rs485_config = ar933x_config_rs485;
 	port->rs485_supported = ar933x_rs485_supported;
+	port->has_sysrq = IS_ENABLED(CONFIG_SERIAL_AR933X_CONSOLE);
 
 	baud = ar933x_uart_get_baud(port->uartclk, AR933X_UART_MAX_SCALE, 1);
 	up->min_baud = max_t(unsigned int, baud, AR933X_UART_MIN_BAUD);
-- 
2.47.3


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