1 files changed, 38 insertions, 2 deletions

diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
index ea6b62cece88..f80a88d107d7 100644
--- a/drivers/tty/serial/sc16is7xx.c
+++ b/drivers/tty/serial/sc16is7xx.c
@@ -332,6 +332,7 @@ struct sc16is7xx_port {
 	struct kthread_worker		kworker;
 	struct task_struct		*kworker_task;
 	struct kthread_work		irq_work;
+	struct mutex			efr_lock;
 	struct sc16is7xx_one		p[0];
 };
 
@@ -503,6 +504,21 @@ static int sc16is7xx_set_baud(struct uart_port *port, int baud)
 		div /= 4;
 	}
 
+	/* In an amazing feat of design, the Enhanced Features Register shares
+	 * the address of the Interrupt Identification Register, and is
+	 * switched in by writing a magic value (0xbf) to the Line Control
+	 * Register. Any interrupt firing during this time will see the EFR
+	 * where it expects the IIR to be, leading to "Unexpected interrupt"
+	 * messages.
+	 *
+	 * Prevent this possibility by claiming a mutex while accessing the
+	 * EFR, and claiming the same mutex from within the interrupt handler.
+	 * This is similar to disabling the interrupt, but that doesn't work
+	 * because the bulk of the interrupt processing is run as a workqueue
+	 * job in thread context.
+	 */
+	mutex_lock(&s->efr_lock);
+
 	lcr = sc16is7xx_port_read(port, SC16IS7XX_LCR_REG);
 
 	/* Open the LCR divisors for configuration */
@@ -518,6 +534,8 @@ static int sc16is7xx_set_baud(struct uart_port *port, int baud)
 	/* Put LCR back to the normal mode */
 	sc16is7xx_port_write(port, SC16IS7XX_LCR_REG, lcr);
 
+	mutex_unlock(&s->efr_lock);
+
 	sc16is7xx_port_update(port, SC16IS7XX_MCR_REG,
 			      SC16IS7XX_MCR_CLKSEL_BIT,
 			      prescaler);
@@ -700,6 +718,8 @@ static void sc16is7xx_ist(struct kthread_work *ws)
 {
 	struct sc16is7xx_port *s = to_sc16is7xx_port(ws, irq_work);
 
+	mutex_lock(&s->efr_lock);
+
 	while (1) {
 		bool keep_polling = false;
 		int i;
@@ -709,6 +729,8 @@ static void sc16is7xx_ist(struct kthread_work *ws)
 		if (!keep_polling)
 			break;
 	}
+
+	mutex_unlock(&s->efr_lock);
 }
 
 static irqreturn_t sc16is7xx_irq(int irq, void *dev_id)
@@ -903,6 +925,9 @@ static void sc16is7xx_set_termios(struct uart_port *port,
 	if (!(termios->c_cflag & CREAD))
 		port->ignore_status_mask |= SC16IS7XX_LSR_BRK_ERROR_MASK;
 
+	/* As above, claim the mutex while accessing the EFR. */
+	mutex_lock(&s->efr_lock);
+
 	sc16is7xx_port_write(port, SC16IS7XX_LCR_REG,
 			     SC16IS7XX_LCR_CONF_MODE_B);
 
@@ -924,6 +949,8 @@ static void sc16is7xx_set_termios(struct uart_port *port,
 	/* Update LCR register */
 	sc16is7xx_port_write(port, SC16IS7XX_LCR_REG, lcr);
 
+	mutex_unlock(&s->efr_lock);
+
 	/* Get baud rate generator configuration */
 	baud = uart_get_baud_rate(port, termios, old,
 				  port->uartclk / 16 / 4 / 0xffff,
@@ -1186,6 +1213,7 @@ static int sc16is7xx_probe(struct device *dev,
 	s->regmap = regmap;
 	s->devtype = devtype;
 	dev_set_drvdata(dev, s);
+	mutex_init(&s->efr_lock);
 
 	kthread_init_worker(&s->kworker);
 	kthread_init_work(&s->irq_work, sc16is7xx_ist);
@@ -1482,7 +1510,7 @@ static int __init sc16is7xx_init(void)
 	ret = i2c_add_driver(&sc16is7xx_i2c_uart_driver);
 	if (ret < 0) {
 		pr_err("failed to init sc16is7xx i2c --> %d\n", ret);
-		return ret;
+		goto err_i2c;
 	}
 #endif
 
@@ -1490,10 +1518,18 @@ static int __init sc16is7xx_init(void)
 	ret = spi_register_driver(&sc16is7xx_spi_uart_driver);
 	if (ret < 0) {
 		pr_err("failed to init sc16is7xx spi --> %d\n", ret);
-		return ret;
+		goto err_spi;
 	}
 #endif
 	return ret;
+
+err_spi:
+#ifdef CONFIG_SERIAL_SC16IS7XX_I2C
+	i2c_del_driver(&sc16is7xx_i2c_uart_driver);
+#endif
+err_i2c:
+	uart_unregister_driver(&sc16is7xx_uart);
+	return ret;
 }
 module_init(sc16is7xx_init);