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>

Documentation/devicetree/bindings/sound/max98357a.txt

@@ -4,7 +4,11 @@ This node models the Maxim MAX98357A DAC.
 
 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:
 

sound/soc/codecs/max98357a.c

@@ -31,6 +31,9 @@ static int max98357a_daiops_trigger(struct snd_pcm_substream *substream,
 {
 	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 @@ static int max98357a_codec_probe(struct snd_soc_codec *codec)
 {
 	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));