iio: stx104: Implement get_multiple callback

The Apex Embedded Systems STX104 series of devices provides 4 TTL
compatible lines of inputs accessed via a single 4-bit port. Since four
input lines are acquired on a single port input read, the STX104 GPIO
driver may improve multiple input reads by utilizing a get_multiple
callback. This patch implements the stx104_gpio_get_multiple function
which serves as the respective get_multiple callback.

Cc: Jonathan Cameron <jic23@kernel.org>
Cc: Hartmut Knaack <knaack.h@gmx.de>
Cc: Lars-Peter Clausen <lars@metafoo.de>
Cc: Peter Meerwald-Stadler <pmeerw@pmeerw.net>
Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/stx104.c

@@ -233,6 +233,16 @@ static int stx104_gpio_get(struct gpio_chip *chip, unsigned int offset)
 	return !!(inb(stx104gpio->base) & BIT(offset));
 }
 
+static int stx104_gpio_get_multiple(struct gpio_chip *chip, unsigned long *mask,
+	unsigned long *bits)
+{
+	struct stx104_gpio *const stx104gpio = gpiochip_get_data(chip);
+
+	*bits = inb(stx104gpio->base);
+
+	return 0;
+}
+
 static void stx104_gpio_set(struct gpio_chip *chip, unsigned int offset,
 	int value)
 {
@@ -342,6 +352,7 @@ static int stx104_probe(struct device *dev, unsigned int id)
 	stx104gpio->chip.direction_input = stx104_gpio_direction_input;
 	stx104gpio->chip.direction_output = stx104_gpio_direction_output;
 	stx104gpio->chip.get = stx104_gpio_get;
+	stx104gpio->chip.get_multiple = stx104_gpio_get_multiple;
 	stx104gpio->chip.set = stx104_gpio_set;
 	stx104gpio->chip.set_multiple = stx104_gpio_set_multiple;
 	stx104gpio->base = base[id] + 3;