gpio: rcar: Optimize GPIO pin state read on R-Car Gen3

Currently, the R-Car GPIO driver treats R-Car Gen2 and R-Car Gen3 GPIO
controllers the same.  However, there exist small differences, like the
behavior of the General Input Register (INDT):
  - On R-Car Gen1, R-Car Gen2, and RZ/G1, INDT only reflects the state
    of an input pin if the GPIO is configured for input,
  - On R-Car Gen3 and RZ/G2, INDT always reflects the state of the input
    pins.
Hence to accommodate all variants, the driver does not use the INDT
register to read the status of a GPIO line when configured for output,
at the expense of doing 2 or 3 register reads instead of 1.

Given register accesses are slow, change the .get() and .get_multiple()
callbacks to always use INDT to read pin state on SoCs where this is
supported.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

drivers/gpio/gpio-rcar.c

@@ -35,6 +35,7 @@ struct gpio_rcar_bank_info {
 struct gpio_rcar_info {
 	bool has_outdtsel;
 	bool has_both_edge_trigger;
+	bool has_always_in;
 };
 
 struct gpio_rcar_priv {
@@ -302,9 +303,11 @@ static int gpio_rcar_get(struct gpio_chip *chip, unsigned offset)
 	struct gpio_rcar_priv *p = gpiochip_get_data(chip);
 	u32 bit = BIT(offset);
 
-	/* testing on r8a7790 shows that INDT does not show correct pin state
-	 * when configured as output, so use OUTDT in case of output pins */
-	if (gpio_rcar_read(p, INOUTSEL) & bit)
+	/*
+	 * Before R-Car Gen3, INDT does not show correct pin state when
+	 * configured as output, so use OUTDT in case of output pins
+	 */
+	if (!p->info.has_always_in && (gpio_rcar_read(p, INOUTSEL) & bit))
 		return !!(gpio_rcar_read(p, OUTDT) & bit);
 	else
 		return !!(gpio_rcar_read(p, INDT) & bit);
@@ -324,6 +327,11 @@ static int gpio_rcar_get_multiple(struct gpio_chip *chip, unsigned long *mask,
 	if (!bankmask)
 		return 0;
 
+	if (p->info.has_always_in) {
+		bits[0] = gpio_rcar_read(p, INDT) & bankmask;
+		return 0;
+	}
+
 	spin_lock_irqsave(&p->lock, flags);
 	outputs = gpio_rcar_read(p, INOUTSEL);
 	m = outputs & bankmask;
@@ -383,11 +391,19 @@ static int gpio_rcar_direction_output(struct gpio_chip *chip, unsigned offset,
 static const struct gpio_rcar_info gpio_rcar_info_gen1 = {
 	.has_outdtsel = false,
 	.has_both_edge_trigger = false,
+	.has_always_in = false,
 };
 
 static const struct gpio_rcar_info gpio_rcar_info_gen2 = {
 	.has_outdtsel = true,
 	.has_both_edge_trigger = true,
+	.has_always_in = false,
+};
+
+static const struct gpio_rcar_info gpio_rcar_info_gen3 = {
+	.has_outdtsel = true,
+	.has_both_edge_trigger = true,
+	.has_always_in = true,
 };
 
 static const struct of_device_id gpio_rcar_of_table[] = {
@@ -399,8 +415,7 @@ static const struct of_device_id gpio_rcar_of_table[] = {
 		.data = &gpio_rcar_info_gen2,
 	}, {
 		.compatible = "renesas,rcar-gen3-gpio",
-		/* Gen3 GPIO is identical to Gen2. */
-		.data = &gpio_rcar_info_gen2,
+		.data = &gpio_rcar_info_gen3,
 	}, {
 		.compatible = "renesas,gpio-rcar",
 		.data = &gpio_rcar_info_gen1,