USB: serial: ftdi_sio: report the valid GPIO lines to gpiolib

Since it is pretty common for only some of the CBUS lines to be
valid as GPIO lines, let's report such validity to the rest of
the kernel.
Signed-off-by: NMarc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20201204164739.781812-3-maz@kernel.orgReviewed-by: NAndy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: NLinus Walleij <linus.walleij@linaro.org>
Signed-off-by: NJohan Hovold <johan@kernel.org>

drivers/usb/serial/ftdi_sio.c

@@ -2002,6 +2002,19 @@ static int ftdi_gpio_direction_output(struct gpio_chip *gc, unsigned int gpio,
 	return result;
 }
 
+static int ftdi_gpio_init_valid_mask(struct gpio_chip *gc,
+				     unsigned long *valid_mask,
+				     unsigned int ngpios)
+{
+	struct usb_serial_port *port = gpiochip_get_data(gc);
+	struct ftdi_private *priv = usb_get_serial_port_data(port);
+	unsigned long map = priv->gpio_altfunc;
+
+	bitmap_complement(valid_mask, &map, ngpios);
+
+	return 0;
+}
+
 static int ftdi_read_eeprom(struct usb_serial *serial, void *dst, u16 addr,
 				u16 nbytes)
 {
@@ -2173,6 +2186,7 @@ static int ftdi_gpio_init(struct usb_serial_port *port)
 	priv->gc.get_direction = ftdi_gpio_direction_get;
 	priv->gc.direction_input = ftdi_gpio_direction_input;
 	priv->gc.direction_output = ftdi_gpio_direction_output;
+	priv->gc.init_valid_mask = ftdi_gpio_init_valid_mask;
 	priv->gc.get = ftdi_gpio_get;
 	priv->gc.set = ftdi_gpio_set;
 	priv->gc.get_multiple = ftdi_gpio_get_multiple;