serial: 8250_omap: Handle optional overrun-throttle-ms property

Handle optional overrun-throttle-ms property as done for 8250_fsl in commit
6d7f677a2a ("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 <[email protected]>
Cc: Merlijn Wajer <[email protected]>
Cc: Pavel Machek <[email protected]>
Cc: Sebastian Reichel <[email protected]>
Cc: Vignesh Raghavendra <[email protected]>
Signed-off-by: Tony Lindgren <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

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);