ASoC: max98357a: Make 'sdmode-gpios' dts property optional

The option is not needed if chip is always on or managed by some other part
of system like platform card driver.

Signed-off-by: Anatol Pomozov <anatol.pomozov@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
diff --git a/Documentation/devicetree/bindings/sound/max98357a.txt b/Documentation/devicetree/bindings/sound/max98357a.txt
index a7a149a..28645a2 100644
--- a/Documentation/devicetree/bindings/sound/max98357a.txt
+++ b/Documentation/devicetree/bindings/sound/max98357a.txt
@@ -4,7 +4,11 @@
 
 Required properties:
 - compatible   : "maxim,max98357a"
-- sdmode-gpios : GPIO specifier for the GPIO -> DAC SDMODE pin
+
+Optional properties:
+- sdmode-gpios : GPIO specifier for the chip's SD_MODE pin.
+        If this option is not specified then driver does not manage
+        the pin state (e.g. chip is always on).
 
 Example:
 
diff --git a/sound/soc/codecs/max98357a.c b/sound/soc/codecs/max98357a.c
index 3a2fda0..fa1b793 100644
--- a/sound/soc/codecs/max98357a.c
+++ b/sound/soc/codecs/max98357a.c
@@ -31,6 +31,9 @@
 {
 	struct gpio_desc *sdmode = snd_soc_dai_get_drvdata(dai);
 
+	if (!sdmode)
+		return 0;
+
 	switch (cmd) {
 	case SNDRV_PCM_TRIGGER_START:
 	case SNDRV_PCM_TRIGGER_RESUME:
@@ -60,7 +63,7 @@
 {
 	struct gpio_desc *sdmode;
 
-	sdmode = devm_gpiod_get(codec->dev, "sdmode", GPIOD_OUT_LOW);
+	sdmode = devm_gpiod_get_optional(codec->dev, "sdmode", GPIOD_OUT_LOW);
 	if (IS_ERR(sdmode)) {
 		dev_err(codec->dev, "%s() unable to get sdmode GPIO: %ld\n",
 				__func__, PTR_ERR(sdmode));