USB: serial: ftdi_sio: add support for FT232H CBUS gpios

Enable support for cbus gpios on FT232H. The cbus configuration is
stored in two words in the EEPROM at byte-offset 0x1a with the mux
config for ACBUS5, ACBUS6, ACBUS8 and ACBUS9 (only pins that can be
configured as I/O mode).

Tested using FT232H by configuring one ACBUS pin at a time.

Reviewed-by: Tim Harvey <tharvey@gateworks.com>
Signed-off-by: Matthew Michilot <matthew.michilot@gmail.com>
[ johan: fix copy-paste error in commit message ]
Signed-off-by: Johan Hovold <johan@kernel.org>

drivers/usb/serial/ftdi_sio.c

@@ -2023,6 +2023,46 @@ static int ftdi_read_eeprom(struct usb_serial *serial, void *dst, u16 addr,
 	return 0;
 }
 
+static int ftdi_gpio_init_ft232h(struct usb_serial_port *port)
+{
+	struct ftdi_private *priv = usb_get_serial_port_data(port);
+	u16 cbus_config;
+	u8 *buf;
+	int ret;
+	int i;
+
+	buf = kmalloc(4, GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+
+	ret = ftdi_read_eeprom(port->serial, buf, 0x1a, 4);
+	if (ret < 0)
+		goto out_free;
+
+	/*
+	 * FT232H CBUS Memory Map
+	 *
+	 * 0x1a: X- (upper nibble -> AC5)
+	 * 0x1b: -X (lower nibble -> AC6)
+	 * 0x1c: XX (upper nibble -> AC9 | lower nibble -> AC8)
+	 */
+	cbus_config = buf[2] << 8 | (buf[1] & 0xf) << 4 | (buf[0] & 0xf0) >> 4;
+
+	priv->gc.ngpio = 4;
+	priv->gpio_altfunc = 0xff;
+
+	for (i = 0; i < priv->gc.ngpio; ++i) {
+		if ((cbus_config & 0xf) == FTDI_FTX_CBUS_MUX_GPIO)
+			priv->gpio_altfunc &= ~BIT(i);
+		cbus_config >>= 4;
+	}
+
+out_free:
+	kfree(buf);
+
+	return ret;
+}
+
 static int ftdi_gpio_init_ft232r(struct usb_serial_port *port)
 {
 	struct ftdi_private *priv = usb_get_serial_port_data(port);
@@ -2098,6 +2138,9 @@ static int ftdi_gpio_init(struct usb_serial_port *port)
 	int result;
 
 	switch (priv->chip_type) {
+	case FT232H:
+		result = ftdi_gpio_init_ft232h(port);
+		break;
 	case FT232RL:
 		result = ftdi_gpio_init_ft232r(port);
 		break;