From 9a1de9db921a0f39445e92e8f4a1a84ea85b43c1 Mon Sep 17 00:00:00 2001

From: Tony Lindgren <tony@atomide.com>

Date: Tue, 27 Jul 2021 13:35:33 +0300

Subject: [PATCH] serial: 8250_omap: Handle optional overrun-throttle-ms property

Git-commit: 1fe0e1fa3209ad8e9124147775bd27b1d9f04bd4

Patch-mainline: v5.15-rc1

References: stable-5.14.6

[ Upstream commit 1fe0e1fa3209ad8e9124147775bd27b1d9f04bd4 ]

Handle optional overrun-throttle-ms property as done for 8250_fsl in commit

6d7f677a2afa ("serial: 8250: Rate limit serial port rx interrupts during

input overruns"). This can be used to rate limit the UART interrupts on

noisy lines that end up producing messages like the following:

ttyS ttyS2: 4 input overrun(s)

At least on droid4, the multiplexed USB and UART port is left to UART mode

by the bootloader for a debug console, and if a USB charger is connected

on boot, we get noise on the UART until the PMIC related drivers for PHY

and charger are loaded.

With this patch and overrun-throttle-ms = <500> we avoid the extra rx

interrupts.

Cc: Carl Philipp Klemm <philipp@uvos.xyz>

Cc: Merlijn Wajer <merlijn@wizzup.org>

Cc: Pavel Machek <pavel@ucw.cz>

Cc: Sebastian Reichel <sre@kernel.org>

Cc: Vignesh Raghavendra <vigneshr@ti.com>

Signed-off-by: Tony Lindgren <tony@atomide.com>

Link: https://lore.kernel.org/r/20210727103533.51547-2-tony@atomide.com

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Signed-off-by: Sasha Levin <sashal@kernel.org>

Acked-by: Takashi Iwai <tiwai@suse.de>

---

 drivers/tty/serial/8250/8250_omap.c | 25 ++++++++++++++++++++++++-

 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c

index 79418d4beb48..b6c731a267d2 100644

--- a/drivers/tty/serial/8250/8250_omap.c

+++ b/drivers/tty/serial/8250/8250_omap.c

@@ -617,7 +617,7 @@ static irqreturn_t omap8250_irq(int irq, void *dev_id)

 	struct uart_port *port = dev_id;

 	struct omap8250_priv *priv = port->private_data;

 	struct uart_8250_port *up = up_to_u8250p(port);

-	unsigned int iir;

+	unsigned int iir, lsr;

 	int ret;

 #ifdef CONFIG_SERIAL_8250_DMA

@@ -628,6 +628,7 @@ static irqreturn_t omap8250_irq(int irq, void *dev_id)

 #endif

 	serial8250_rpm_get(up);

+	lsr = serial_port_in(port, UART_LSR);

 	iir = serial_port_in(port, UART_IIR);

 	ret = serial8250_handle_irq(port, iir);

@@ -642,6 +643,24 @@ static irqreturn_t omap8250_irq(int irq, void *dev_id)

 		serial_port_in(port, UART_RX);

 	}

+	/* Stop processing interrupts on input overrun */

+	if ((lsr & UART_LSR_OE) && up->overrun_backoff_time_ms > 0) {

+		unsigned long delay;

+

+		up->ier = port->serial_in(port, UART_IER);

+		if (up->ier & (UART_IER_RLSI | UART_IER_RDI)) {

+			port->ops->stop_rx(port);

+		} else {

+			/* Keep restarting the timer until

+			 * the input overrun subsides.

+			 */

+			cancel_delayed_work(&up->overrun_backoff);

+		}

+

+		delay = msecs_to_jiffies(up->overrun_backoff_time_ms);

+		schedule_delayed_work(&up->overrun_backoff, delay);

+	}

+

 	serial8250_rpm_put(up);

 	return IRQ_RETVAL(ret);

@@ -1353,6 +1372,10 @@ static int omap8250_probe(struct platform_device *pdev)

 		}

 	}

+	if (of_property_read_u32(np, "overrun-throttle-ms",

+				 &up.overrun_backoff_time_ms) != 0)

+		up.overrun_backoff_time_ms = 0;

+

 	priv->wakeirq = irq_of_parse_and_map(np, 1);

 	pdata = of_device_get_match_data(&pdev->dev);

-- 

2.26.2