ASoC: codecs: dmic: Make number of channels configurable

The DMIC DAI driver specifies a number of 1 to 8 channels for each DAI.
The actual number of mics can currently not be configured in the device
tree or audio glue, but is derived from the min/max channels of the CPU
and codec DAI. A typical CPU DAI has two or more channels, in consequence
a single mic is treated as a stereo/multi channel device, even though
only one channel carries audio data.

This change adds the option to specify the number of used DMIC channels
in the device tree. When specified this value overwrites the default
channels_max value of 8 in the snd_soc_dai_driver struct of the codec.
Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Arnaud Pouliquen <arnaud.pouliquen@st.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/dmic.txt

@@ -7,10 +7,12 @@ Required properties:
 
 Optional properties:
 	- dmicen-gpios: GPIO specifier for dmic to control start and stop
+	- num-channels: Number of microphones on this DAI
 
 Example node:
 
 	dmic_codec: dmic@0 {
 		compatible = "dmic-codec";
 		dmicen-gpios = <&gpio4 3 GPIO_ACTIVE_HIGH>;
+		num-channels = <1>;
 	};

sound/soc/codecs/dmic.c

@@ -107,8 +107,30 @@ static const struct snd_soc_codec_driver soc_dmic = {
 
 static int dmic_dev_probe(struct platform_device *pdev)
 {
+	int err;
+	u32 chans;
+	struct snd_soc_dai_driver *dai_drv = &dmic_dai;
+
+	if (pdev->dev.of_node) {
+		err = of_property_read_u32(pdev->dev.of_node, "num-channels", &chans);
+		if (err && (err != -ENOENT))
+			return err;
+
+		if (!err) {
+			if (chans < 1 || chans > 8)
+				return -EINVAL;
+
+			dai_drv = devm_kzalloc(&pdev->dev, sizeof(*dai_drv), GFP_KERNEL);
+			if (!dai_drv)
+				return -ENOMEM;
+
+			memcpy(dai_drv, &dmic_dai, sizeof(*dai_drv));
+			dai_drv->capture.channels_max = chans;
+		}
+	}
+
 	return snd_soc_register_codec(&pdev->dev,
-			&soc_dmic, &dmic_dai, 1);
+			&soc_dmic, dai_drv, 1);
 }
 
 static int dmic_dev_remove(struct platform_device *pdev)