[PATCH 5.14 265/432] serial: 8250_omap: Handle optional overrun-throttle-ms property

Greg Kroah-Hartman
2021-09-16T17:37:44Z

From: Tony Lindgren <tony@atomide.com>

[ 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>
---
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);
--
2.30.2