NFC: Make EN2 pin optional in the TRF7970A driver

Make the EN2 pin optional. This is useful for boards,
which have this pin fix wired, for example to ground.
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Guan Ben <ben.guan@cn.bosch.com>
Signed-off-by: Mark Jonas <mark.jonas@de.bosch.com>
Signed-off-by: Heiko Schocher <hs@denx.de>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>

Documentation/devicetree/bindings/net/nfc/trf7970a.txt

@@ -5,8 +5,8 @@ Required properties:
 - spi-max-frequency: Maximum SPI frequency (<= 2000000).
 - interrupt-parent: phandle of parent interrupt handler.
 - interrupts: A single interrupt specifier.
-- ti,enable-gpios: Two GPIO entries used for 'EN' and 'EN2' pins on the
-  TRF7970A.
+- ti,enable-gpios: One or two GPIO entries used for 'EN' and 'EN2' pins on the
+  TRF7970A. EN2 is optional.
 - vin-supply: Regulator for supply voltage to VIN pin
 
 Optional SoC Specific Properties:

drivers/nfc/trf7970a.c

@@ -1885,9 +1885,11 @@ static int trf7970a_power_up(struct trf7970a *trf)
 	usleep_range(5000, 6000);
 
 	if (!(trf->quirks & TRF7970A_QUIRK_EN2_MUST_STAY_LOW)) {
+		if (gpio_is_valid(trf->en2_gpio)) {
 			gpio_set_value(trf->en2_gpio, 1);
 			usleep_range(1000, 2000);
 		}
+	}
 
 	gpio_set_value(trf->en_gpio, 1);
 
@@ -1914,6 +1916,7 @@ static int trf7970a_power_down(struct trf7970a *trf)
 	}
 
 	gpio_set_value(trf->en_gpio, 0);
+	if (gpio_is_valid(trf->en2_gpio))
 		gpio_set_value(trf->en2_gpio, 0);
 
 	ret = regulator_disable(trf->regulator);
@@ -2032,16 +2035,15 @@ static int trf7970a_probe(struct spi_device *spi)
 
 	trf->en2_gpio = of_get_named_gpio(np, "ti,enable-gpios", 1);
 	if (!gpio_is_valid(trf->en2_gpio)) {
-		dev_err(trf->dev, "No EN2 GPIO property\n");
-		return trf->en2_gpio;
-	}
-
+		dev_info(trf->dev, "No EN2 GPIO property\n");
+	} else {
 		ret = devm_gpio_request_one(trf->dev, trf->en2_gpio,
 				GPIOF_DIR_OUT | GPIOF_INIT_LOW, "trf7970a EN2");
 		if (ret) {
 			dev_err(trf->dev, "Can't request EN2 GPIO: %d\n", ret);
 			return ret;
 		}
+	}
 
 	if (of_property_read_bool(np, "en2-rf-quirk"))
 		trf->quirks |= TRF7970A_QUIRK_EN2_MUST_STAY_LOW;