sc16is7xx: Fix for "Unexpected interrupt: 8"
[ Upstream commit 30ec514d440cf2c472c8e4b0079af2c731f71a3e ]
The SC16IS752 has an Enhanced Feature Register which is aliased at the
same address as the Interrupt Identification Register; accessing it
requires that a magic value is written to the Line Configuration
Register. If an interrupt is raised while the EFR is mapped in then
the ISR won't be able to access the IIR, leading to the "Unexpected
interrupt" error messages.
Avoid the problem by claiming a mutex around accesses to the EFR
register, also claiming the mutex in the interrupt handler work
item (this is equivalent to disabling interrupts to interlock against
a non-threaded interrupt handler).
See: https://github.com/raspberrypi/linux/issues/2529
Signed-off-by: Phil Elwell <phil@raspberrypi.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
index 82451bb6..f80a88d 100644
--- a/drivers/tty/serial/sc16is7xx.c
+++ b/drivers/tty/serial/sc16is7xx.c
@@ -332,6 +332,7 @@
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 @@
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 @@
/* 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 @@
{
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 @@
if (!keep_polling)
break;
}
+
+ mutex_unlock(&s->efr_lock);
}
static irqreturn_t sc16is7xx_irq(int irq, void *dev_id)
@@ -903,6 +925,9 @@
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 @@
/* 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 @@
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);