gpio: 74x164: Implement gpiochip.set_multiple()

This allows to set multiple outputs using a single SPI transfer.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Phil Reid <preid@electromag.com.au>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/gpio-74x164.c

@@ -75,6 +75,29 @@ static void gen_74x164_set_value(struct gpio_chip *gc,
 	mutex_unlock(&chip->lock);
 }
 
+static void gen_74x164_set_multiple(struct gpio_chip *gc, unsigned long *mask,
+				    unsigned long *bits)
+{
+	struct gen_74x164_chip *chip = gpiochip_get_data(gc);
+	unsigned int i, idx, shift;
+	u8 bank, bankmask;
+
+	mutex_lock(&chip->lock);
+	for (i = 0, bank = chip->registers - 1; i < chip->registers;
+	     i++, bank--) {
+		idx = i / sizeof(*mask);
+		shift = i % sizeof(*mask) * BITS_PER_BYTE;
+		bankmask = mask[idx] >> shift;
+		if (!bankmask)
+			continue;
+
+		chip->buffer[bank] &= ~bankmask;
+		chip->buffer[bank] |= bankmask & (bits[idx] >> shift);
+	}
+	__gen_74x164_write_config(chip);
+	mutex_unlock(&chip->lock);
+}
+
 static int gen_74x164_direction_output(struct gpio_chip *gc,
 		unsigned offset, int val)
 {
@@ -114,6 +137,7 @@ static int gen_74x164_probe(struct spi_device *spi)
 	chip->gpio_chip.direction_output = gen_74x164_direction_output;
 	chip->gpio_chip.get = gen_74x164_get_value;
 	chip->gpio_chip.set = gen_74x164_set_value;
+	chip->gpio_chip.set_multiple = gen_74x164_set_multiple;
 	chip->gpio_chip.base = -1;
 
 	chip->registers = nregs;