ASoC: wm8994: Support constraining the maximum number of channels clocked

Some systems use the audio CODEC to clock a DAI with multiple data lines
in parallel, meaning that bit clocks are only required for a smaller number
of channels than data is sent for. In some cases providing the extra bit
clocks can take the other devices on the audio bus out of spec.

Support such systems by allowing a maximum number of channels to be
specified.
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

include/linux/mfd/wm8994/pdata.h

@@ -17,6 +17,7 @@
 
 #define WM8994_NUM_LDO   2
 #define WM8994_NUM_GPIO 11
+#define WM8994_NUM_AIF   3
 
 struct wm8994_ldo_pdata {
 	/** GPIOs to enable regulator, 0 or less if not available */
@@ -215,6 +216,13 @@ struct wm8994_pdata {
 	 * system.
 	 */
 	bool spkmode_pu;
+
+	/**
+	 * Maximum number of channels clocks will be generated for,
+	 * useful for systems where and I2S bus with multiple data
+	 * lines is mastered.
+	 */
+	int max_channels_clocked[WM8994_NUM_AIF];
 };
 
 #endif

sound/soc/codecs/wm8994.c

@@ -2656,6 +2656,8 @@ static int wm8994_hw_params(struct snd_pcm_substream *substream,
 {
 	struct snd_soc_codec *codec = dai->codec;
 	struct wm8994_priv *wm8994 = snd_soc_codec_get_drvdata(codec);
+	struct wm8994 *control = wm8994->wm8994;
+	struct wm8994_pdata *pdata = &control->pdata;
 	int aif1_reg;
 	int aif2_reg;
 	int bclk_reg;
@@ -2723,7 +2725,14 @@ static int wm8994_hw_params(struct snd_pcm_substream *substream,
 	}
 
 	wm8994->channels[id] = params_channels(params);
-	switch (params_channels(params)) {
+	if (pdata->max_channels_clocked[id] &&
+	    wm8994->channels[id] > pdata->max_channels_clocked[id]) {
+		dev_dbg(dai->dev, "Constraining channels to %d from %d\n",
+			pdata->max_channels_clocked[id], wm8994->channels[id]);
+		wm8994->channels[id] = pdata->max_channels_clocked[id];
+	}
+
+	switch (wm8994->channels[id]) {
 	case 1:
 	case 2:
 		bclk_rate *= 2;
@@ -2745,7 +2754,7 @@ static int wm8994_hw_params(struct snd_pcm_substream *substream,
 	dev_dbg(dai->dev, "AIF%dCLK is %dHz, target BCLK %dHz\n",
 		dai->id, wm8994->aifclk[id], bclk_rate);
 
-	if (params_channels(params) == 1 &&
+	if (wm8994->channels[id] == 1 &&
 	    (snd_soc_read(codec, aif1_reg) & 0x18) == 0x18)
 		aif2 |= WM8994_AIF1_MONO;