USB: serial: cp210x: fix CP2105 GPIO registration

When generalising GPIO support and adding support for CP2102N, the GPIO
registration for some CP2105 devices accidentally broke. Specifically,
when all the pins of a port are in "modem" mode, and thus unavailable
for GPIO use, the GPIO chip would now be registered without having
initialised the number of GPIO lines. This would in turn be rejected by
gpiolib and some errors messages would be printed (but importantly probe
would still succeed).

Fix this by initialising the number of GPIO lines before registering the
GPIO chip.

Note that as for the other device types, and as when all CP2105 pins are
muxed for LED function, the GPIO chip is registered also when no pins
are available for GPIO use.

Reported-by: Maarten Brock <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Fixes: c8acfe0 ("USB: serial: cp210x: implement GPIO support for CP2102N")
Cc: [email protected]      # 4.19
Cc: Karoly Pados <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Greg Kroah-Hartman <[email protected]>
Tested-by: Maarten Brock <[email protected]>
Signed-off-by: Johan Hovold <[email protected]>

Author: jhovold

drivers/usb/serial/cp210x.c

@@ -1635,6 +1635,8 @@ static int cp2105_gpioconf_init(struct usb_serial *serial)
 
 	/*  2 banks of GPIO - One for the pins taken from each serial port */
 	if (intf_num == 0) {
+		priv->gc.ngpio = 2;
+
 		if (mode.eci == CP210X_PIN_MODE_MODEM) {
 			/* mark all GPIOs of this interface as reserved */
 			priv->gpio_altfunc = 0xff;
@@ -1645,8 +1647,9 @@ static int cp2105_gpioconf_init(struct usb_serial *serial)
 		priv->gpio_pushpull = (u8)((le16_to_cpu(config.gpio_mode) &
 						CP210X_ECI_GPIO_MODE_MASK) >>
 						CP210X_ECI_GPIO_MODE_OFFSET);
-		priv->gc.ngpio = 2;
 	} else if (intf_num == 1) {
+		priv->gc.ngpio = 3;
+
 		if (mode.sci == CP210X_PIN_MODE_MODEM) {
 			/* mark all GPIOs of this interface as reserved */
 			priv->gpio_altfunc = 0xff;
@@ -1657,7 +1660,6 @@ static int cp2105_gpioconf_init(struct usb_serial *serial)
 		priv->gpio_pushpull = (u8)((le16_to_cpu(config.gpio_mode) &
 						CP210X_SCI_GPIO_MODE_MASK) >>
 						CP210X_SCI_GPIO_MODE_OFFSET);
-		priv->gc.ngpio = 3;
 	} else {
 		return -ENODEV;
 	}