serial: 8250_pci: Correct uartclk for xr17v35x expansion chips

commit 899f0c1c upstream.

The internal clock of the master chip, which is usually 125MHz, is only half
(62.5MHz) for the slave chips. So we have to adjust the uartclk for all the
slave ports. Therefor we add a new function to determine if a slave chip is
present and update pci_xr17v35x_setup accordingly.
Signed-off-by: Soeren Grunewald <soeren.grunewald@desy.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

drivers/tty/serial/8250/8250_pci.c

@@ -1634,6 +1634,9 @@ static int pci_eg20t_init(struct pci_dev *dev)
 #endif
 }
 
+#define PCI_DEVICE_ID_EXAR_XR17V4358	0x4358
+#define PCI_DEVICE_ID_EXAR_XR17V8358	0x8358
+
 static int
 pci_xr17c154_setup(struct serial_private *priv,
 		  const struct pciserial_board *board,
@@ -1643,6 +1646,15 @@ pci_xr17c154_setup(struct serial_private *priv,
 	return pci_default_setup(priv, board, port, idx);
 }
 
+static inline int
+xr17v35x_has_slave(struct serial_private *priv)
+{
+	const int dev_id = priv->dev->device;
+
+	return ((dev_id == PCI_DEVICE_ID_EXAR_XR17V4358) ||
+	        (dev_id == PCI_DEVICE_ID_EXAR_XR17V8358));
+}
+
 static int
 pci_xr17v35x_setup(struct serial_private *priv,
 		  const struct pciserial_board *board,
@@ -1656,6 +1668,13 @@ pci_xr17v35x_setup(struct serial_private *priv,
 
 	port->port.flags |= UPF_EXAR_EFR;
 
+	/*
+	 * Setup the uart clock for the devices on expansion slot to
+	 * half the clock speed of the main chip (which is 125MHz)
+	 */
+	if (xr17v35x_has_slave(priv) && idx >= 8)
+		port->port.uartclk = (7812500 * 16 / 2);
+
 	/*
 	 * Setup Multipurpose Input/Output pins.
 	 */
@@ -1802,9 +1821,6 @@ pci_wch_ch353_setup(struct serial_private *priv,
 #define PCI_DEVICE_ID_PERICOM_PI7C9X7954	0x7954
 #define PCI_DEVICE_ID_PERICOM_PI7C9X7958	0x7958
 
-#define PCI_DEVICE_ID_EXAR_XR17V4358	0x4358
-#define PCI_DEVICE_ID_EXAR_XR17V8358	0x8358
-
 /* Unknown vendors/cards - this should not be in linux/pci_ids.h */
 #define PCI_SUBDEVICE_ID_UNKNOWN_0x1584	0x1584
 #define PCI_SUBDEVICE_ID_UNKNOWN_0x1588	0x1588