[PATCH 4.18 21/35] serial: 8250_exar: Read INT0 from slave device, too

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Aaron Sierra <asierra@xes-inc.com>

commit 60ab0fafc4b652fcaf7cbc3bb8555a0cf1149c28 upstream.

The sleep wake-up refactoring that I introduced in

  commit c7e1b4059075 ("tty: serial: exar: Relocate sleep wake-up handling")

did not account for devices with a slave device on the expansion port.
This patch pokes the INT0 register in the slave device, if present, in
order to ensure that MSI interrupts don't get permanently "stuck"
because of a sleep wake-up interrupt as described here:

  commit 2c0ac5b48a35 ("serial: exar: Fix stuck MSIs")

This also converts an ioread8() to readb() in order to provide visual
consistency with the MMIO-only accessors used elsewhere in the driver.

Reported-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Aaron Sierra <asierra@xes-inc.com>
Fixes: c7e1b4059075 ("tty: serial: exar: Relocate sleep wake-up handling")
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/tty/serial/8250/8250_exar.c |    6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/drivers/tty/serial/8250/8250_exar.c
+++ b/drivers/tty/serial/8250/8250_exar.c
@@ -433,7 +433,11 @@ static irqreturn_t exar_misc_handler(int
 	struct exar8250 *priv = data;
 
 	/* Clear all PCI interrupts by reading INT0. No effect on IIR */
-	ioread8(priv->virt + UART_EXAR_INT0);
+	readb(priv->virt + UART_EXAR_INT0);
+
+	/* Clear INT0 for Expansion Interface slave ports, too */
+	if (priv->board->num_ports > 8)
+		readb(priv->virt + 0x2000 + UART_EXAR_INT0);
 
 	return IRQ_HANDLED;
 }