[RFC] ASoC: wm8741: Add differential mono mode support
diff mbox

Message ID 1430504037-7170-1-git-send-email-ce3a@gmx.de
State New
Headers show

Commit Message

Sergej Sawazki May 1, 2015, 6:13 p.m. UTC
The WM8741 DAC supports several differential output modes (stereo,
stereo reversed, mono left, mono right). Add platform data and DT
bindings to configure it.

Signed-off-by: Sergej Sawazki <ce3a@gmx.de>
---
 Documentation/devicetree/bindings/sound/wm8741.txt |  11 ++
 sound/soc/codecs/wm8741.c                          | 129 ++++++++++++++++++---
 sound/soc/codecs/wm8741.h                          |  10 ++
 3 files changed, 137 insertions(+), 13 deletions(-)

Comments

Charles Keepax May 4, 2015, 8:02 a.m. UTC | #1
On Fri, May 01, 2015 at 08:13:57PM +0200, Sergej Sawazki wrote:
> The WM8741 DAC supports several differential output modes (stereo,
> stereo reversed, mono left, mono right). Add platform data and DT
> bindings to configure it.
> 
> Signed-off-by: Sergej Sawazki <ce3a@gmx.de>
> ---
>  Documentation/devicetree/bindings/sound/wm8741.txt |  11 ++
>  sound/soc/codecs/wm8741.c                          | 129 ++++++++++++++++++---
>  sound/soc/codecs/wm8741.h                          |  10 ++
>  3 files changed, 137 insertions(+), 13 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/sound/wm8741.txt b/Documentation/devicetree/bindings/sound/wm8741.txt
> index 74bda58..a133154 100644
> --- a/Documentation/devicetree/bindings/sound/wm8741.txt
> +++ b/Documentation/devicetree/bindings/sound/wm8741.txt
> @@ -10,9 +10,20 @@ Required properties:
>    - reg : the I2C address of the device for I2C, the chip select
>            number for SPI.
>  
> +Optional properties:
> +
> +  - diff-mode: Differential output mode configuration. Default value for field
> +    DIFF in register R8 (MODE_CONTROL_2). If absent, the default is 0, shall be:
> +    0 = stereo
> +    1 = mono left
> +    2 = stereo reversed
> +    3 = mono right
> +
>  Example:
>  
>  codec: wm8741@1a {
>  	compatible = "wlf,wm8741";
>  	reg = <0x1a>;
> +
> +	diff-mode = <3>;
>  };
> diff --git a/sound/soc/codecs/wm8741.c b/sound/soc/codecs/wm8741.c
> index 9e71c76..9b777a6 100644
> --- a/sound/soc/codecs/wm8741.c
> +++ b/sound/soc/codecs/wm8741.c
> @@ -41,6 +41,7 @@ static const char *wm8741_supply_names[WM8741_NUM_SUPPLIES] = {
>  
>  /* codec private data */
>  struct wm8741_priv {
> +	struct wm8741_platform_data pdata;
>  	struct regmap *regmap;
>  	struct regulator_bulk_data supplies[WM8741_NUM_SUPPLIES];
>  	unsigned int sysclk;
> @@ -87,13 +88,27 @@ static int wm8741_reset(struct snd_soc_codec *codec)
>  static const DECLARE_TLV_DB_SCALE(dac_tlv_fine, -12700, 13, 0);
>  static const DECLARE_TLV_DB_SCALE(dac_tlv, -12700, 400, 0);
>  
> -static const struct snd_kcontrol_new wm8741_snd_controls[] = {
> +static const struct snd_kcontrol_new wm8741_snd_controls_stereo[] = {
>  SOC_DOUBLE_R_TLV("Fine Playback Volume", WM8741_DACLLSB_ATTENUATION,
>  		 WM8741_DACRLSB_ATTENUATION, 1, 255, 1, dac_tlv_fine),
>  SOC_DOUBLE_R_TLV("Playback Volume", WM8741_DACLMSB_ATTENUATION,
>  		 WM8741_DACRMSB_ATTENUATION, 0, 511, 1, dac_tlv),
>  };
>  
> +static const struct snd_kcontrol_new wm8741_snd_controls_mono_left[] = {
> +SOC_SINGLE_TLV("Fine Playback Volume Left", WM8741_DACLLSB_ATTENUATION,
> +		 1, 255, 1, dac_tlv_fine),
> +SOC_SINGLE_TLV("Playback Volume Left", WM8741_DACLMSB_ATTENUATION,
> +		 0, 511, 1, dac_tlv),
> +};
> +
> +static const struct snd_kcontrol_new wm8741_snd_controls_mono_right[] = {
> +	SOC_SINGLE_TLV("Fine Playback Volume Right", WM8741_DACRLSB_ATTENUATION,
> +		1, 255, 1, dac_tlv_fine),
> +	SOC_SINGLE_TLV("Playback Volume Right", WM8741_DACRMSB_ATTENUATION,
> +		0, 511, 1, dac_tlv),
> +};
> +

Tabbing here could use being fixed, but functionally the change
looks fine to me.

Acked-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>

Thanks,
Charles
Mark Brown May 4, 2015, 11:25 a.m. UTC | #2
On Fri, May 01, 2015 at 08:13:57PM +0200, Sergej Sawazki wrote:

> +static const struct snd_kcontrol_new wm8741_snd_controls_mono_right[] = {
> +	SOC_SINGLE_TLV("Fine Playback Volume Right", WM8741_DACRLSB_ATTENUATION,
> +		1, 255, 1, dac_tlv_fine),
> +	SOC_SINGLE_TLV("Playback Volume Right", WM8741_DACRMSB_ATTENUATION,
> +		0, 511, 1, dac_tlv),
> +};

Please follow the control naming standard in ControlNames.txt: all
volume controls must have Volume as the last word in the name.

>  	.name = "wm8741",
>  	.playback = {
>  		.stream_name = "Playback",
> -		.channels_min = 2,  /* Mono modes not yet supported */
> +		.channels_min = 1,
>  		.channels_max = 2,

This should be varying with the platform data: in the mono modes we
can't do stereo and I suspect the stereo modes may have issues with
mono.
Sergej Sawazki May 4, 2015, 7:03 p.m. UTC | #3
Am 04.05.2015 um 13:25 schrieb Mark Brown:
> On Fri, May 01, 2015 at 08:13:57PM +0200, Sergej Sawazki wrote:
>
>> +static const struct snd_kcontrol_new wm8741_snd_controls_mono_right[] = {
>> +	SOC_SINGLE_TLV("Fine Playback Volume Right", WM8741_DACRLSB_ATTENUATION,
>> +		1, 255, 1, dac_tlv_fine),
>> +	SOC_SINGLE_TLV("Playback Volume Right", WM8741_DACRMSB_ATTENUATION,
>> +		0, 511, 1, dac_tlv),
>> +};
>
> Please follow the control naming standard in ControlNames.txt: all
> volume controls must have Volume as the last word in the name.

Thanks for this information. I would suggest "Right Fine Playback
Volume". Where "Right" is the "CHANNEL" from ControlNames.txt.
However, there is no "Right" in the "CHANNEL" section.
What do you think?

>>   	.name = "wm8741",
>>   	.playback = {
>>   		.stream_name = "Playback",
>> -		.channels_min = 2,  /* Mono modes not yet supported */
>> +		.channels_min = 1,
>>   		.channels_max = 2,
>
> This should be varying with the platform data: in the mono modes we
> can't do stereo and I suspect the stereo modes may have issues with
> mono.

I think this should be always ".channels_min = 2". In "mono mode"
the DAC plays either the right or the left channel, however the I2S
signal is expected to be stereo.

Sergej
Mark Brown May 5, 2015, 11:22 a.m. UTC | #4
On Mon, May 04, 2015 at 09:03:56PM +0200, Sergej Sawazki wrote:
> Am 04.05.2015 um 13:25 schrieb Mark Brown:
> >On Fri, May 01, 2015 at 08:13:57PM +0200, Sergej Sawazki wrote:
> >
> >>+static const struct snd_kcontrol_new wm8741_snd_controls_mono_right[] = {
> >>+	SOC_SINGLE_TLV("Fine Playback Volume Right", WM8741_DACRLSB_ATTENUATION,
> >>+		1, 255, 1, dac_tlv_fine),
> >>+	SOC_SINGLE_TLV("Playback Volume Right", WM8741_DACRMSB_ATTENUATION,
> >>+		0, 511, 1, dac_tlv),
> >>+};

> >Please follow the control naming standard in ControlNames.txt: all
> >volume controls must have Volume as the last word in the name.

> Thanks for this information. I would suggest "Right Fine Playback
> Volume". Where "Right" is the "CHANNEL" from ControlNames.txt.
> However, there is no "Right" in the "CHANNEL" section.
> What do you think?

If the device is in a mono mode it shouldn't have Left or Right in the
control name at all.

> >>  	.playback = {
> >>  		.stream_name = "Playback",
> >>-		.channels_min = 2,  /* Mono modes not yet supported */
> >>+		.channels_min = 1,
> >>  		.channels_max = 2,

> >This should be varying with the platform data: in the mono modes we
> >can't do stereo and I suspect the stereo modes may have issues with
> >mono.

> I think this should be always ".channels_min = 2". In "mono mode"
> the DAC plays either the right or the left channel, however the I2S
> signal is expected to be stereo.

Does the device only do I2S or can it do DSP modes as well (and if it
does are they OK with an actual mono signal)?
Sergej Sawazki May 5, 2015, 12:19 p.m. UTC | #5
Am 5. Mai 2015 13:22:39 MESZ, schrieb Mark Brown <broonie@kernel.org>:
>On Mon, May 04, 2015 at 09:03:56PM +0200, Sergej Sawazki wrote:
>> Am 04.05.2015 um 13:25 schrieb Mark Brown:
>> >On Fri, May 01, 2015 at 08:13:57PM +0200, Sergej Sawazki wrote:
>> >
>> >>+static const struct snd_kcontrol_new
>wm8741_snd_controls_mono_right[] = {
>> >>+	SOC_SINGLE_TLV("Fine Playback Volume Right",
>WM8741_DACRLSB_ATTENUATION,
>> >>+		1, 255, 1, dac_tlv_fine),
>> >>+	SOC_SINGLE_TLV("Playback Volume Right",
>WM8741_DACRMSB_ATTENUATION,
>> >>+		0, 511, 1, dac_tlv),
>> >>+};
>
>> >Please follow the control naming standard in ControlNames.txt: all
>> >volume controls must have Volume as the last word in the name.
>
>> Thanks for this information. I would suggest "Right Fine Playback
>> Volume". Where "Right" is the "CHANNEL" from ControlNames.txt.
>> However, there is no "Right" in the "CHANNEL" section.
>> What do you think?
>
>If the device is in a mono mode it shouldn't have Left or Right in the
>control name at all.

The mono mode of the device should not be confused
with the ALSA mono mode. If the device is in mono mode
it either plays the left (mono left mode) or the right (mono
right mode) channel.

My board has two of this DACs (left and right channel). 
The control names should be different, hence my
suggestion for the "Left" and "Right" prefixes.

Another approach would be to say that the machine
driver is responsible for mixer controls if the devices
are in mono mode. What do you think?

>> >>  	.playback = {
>> >>  		.stream_name = "Playback",
>> >>-		.channels_min = 2,  /* Mono modes not yet supported */
>> >>+		.channels_min = 1,
>> >>  		.channels_max = 2,
>
>> >This should be varying with the platform data: in the mono modes we
>> >can't do stereo and I suspect the stereo modes may have issues with
>> >mono.
>
>> I think this should be always ".channels_min = 2". In "mono mode"
>> the DAC plays either the right or the left channel, however the I2S
>> signal is expected to be stereo.
>
>Does the device only do I2S or can it do DSP modes as well (and if it
>does are they OK with an actual mono signal)?

It can do DSP A and B, but they do not support an actual
mono signal (left + right only).
Mark Brown May 5, 2015, 1:57 p.m. UTC | #6
On Tue, May 05, 2015 at 02:19:38PM +0200, Sergej Sawazki wrote:

> The mono mode of the device should not be confused
> with the ALSA mono mode. If the device is in mono mode
> it either plays the left (mono left mode) or the right (mono
> right mode) channel.

> My board has two of this DACs (left and right channel). 
> The control names should be different, hence my
> suggestion for the "Left" and "Right" prefixes.

That's fine and totally normal.

> Another approach would be to say that the machine
> driver is responsible for mixer controls if the devices
> are in mono mode. What do you think?

Yes, the machine driver should do this - you may have left and right on
your board but these configurations are for example often used with 5.1
systems.
Sergej Sawazki May 5, 2015, 2:07 p.m. UTC | #7
Am 5. Mai 2015 15:57:31 MESZ, schrieb Mark Brown <broonie@kernel.org>:
>On Tue, May 05, 2015 at 02:19:38PM +0200, Sergej Sawazki wrote:
>
>> The mono mode of the device should not be confused
>> with the ALSA mono mode. If the device is in mono mode
>> it either plays the left (mono left mode) or the right (mono
>> right mode) channel.
>
>> My board has two of this DACs (left and right channel). 
>> The control names should be different, hence my
>> suggestion for the "Left" and "Right" prefixes.
>
>That's fine and totally normal.
>
>> Another approach would be to say that the machine
>> driver is responsible for mixer controls if the devices
>> are in mono mode. What do you think?
>
>Yes, the machine driver should do this - you may have left and right on
>your board but these configurations are for example often used with 5.1
>systems.

Good point. Thanks. I am going to resend the patch as v2.

Patch
diff mbox

diff --git a/Documentation/devicetree/bindings/sound/wm8741.txt b/Documentation/devicetree/bindings/sound/wm8741.txt
index 74bda58..a133154 100644
--- a/Documentation/devicetree/bindings/sound/wm8741.txt
+++ b/Documentation/devicetree/bindings/sound/wm8741.txt
@@ -10,9 +10,20 @@  Required properties:
   - reg : the I2C address of the device for I2C, the chip select
           number for SPI.
 
+Optional properties:
+
+  - diff-mode: Differential output mode configuration. Default value for field
+    DIFF in register R8 (MODE_CONTROL_2). If absent, the default is 0, shall be:
+    0 = stereo
+    1 = mono left
+    2 = stereo reversed
+    3 = mono right
+
 Example:
 
 codec: wm8741@1a {
 	compatible = "wlf,wm8741";
 	reg = <0x1a>;
+
+	diff-mode = <3>;
 };
diff --git a/sound/soc/codecs/wm8741.c b/sound/soc/codecs/wm8741.c
index 9e71c76..9b777a6 100644
--- a/sound/soc/codecs/wm8741.c
+++ b/sound/soc/codecs/wm8741.c
@@ -41,6 +41,7 @@  static const char *wm8741_supply_names[WM8741_NUM_SUPPLIES] = {
 
 /* codec private data */
 struct wm8741_priv {
+	struct wm8741_platform_data pdata;
 	struct regmap *regmap;
 	struct regulator_bulk_data supplies[WM8741_NUM_SUPPLIES];
 	unsigned int sysclk;
@@ -87,13 +88,27 @@  static int wm8741_reset(struct snd_soc_codec *codec)
 static const DECLARE_TLV_DB_SCALE(dac_tlv_fine, -12700, 13, 0);
 static const DECLARE_TLV_DB_SCALE(dac_tlv, -12700, 400, 0);
 
-static const struct snd_kcontrol_new wm8741_snd_controls[] = {
+static const struct snd_kcontrol_new wm8741_snd_controls_stereo[] = {
 SOC_DOUBLE_R_TLV("Fine Playback Volume", WM8741_DACLLSB_ATTENUATION,
 		 WM8741_DACRLSB_ATTENUATION, 1, 255, 1, dac_tlv_fine),
 SOC_DOUBLE_R_TLV("Playback Volume", WM8741_DACLMSB_ATTENUATION,
 		 WM8741_DACRMSB_ATTENUATION, 0, 511, 1, dac_tlv),
 };
 
+static const struct snd_kcontrol_new wm8741_snd_controls_mono_left[] = {
+SOC_SINGLE_TLV("Fine Playback Volume Left", WM8741_DACLLSB_ATTENUATION,
+		 1, 255, 1, dac_tlv_fine),
+SOC_SINGLE_TLV("Playback Volume Left", WM8741_DACLMSB_ATTENUATION,
+		 0, 511, 1, dac_tlv),
+};
+
+static const struct snd_kcontrol_new wm8741_snd_controls_mono_right[] = {
+	SOC_SINGLE_TLV("Fine Playback Volume Right", WM8741_DACRLSB_ATTENUATION,
+		1, 255, 1, dac_tlv_fine),
+	SOC_SINGLE_TLV("Playback Volume Right", WM8741_DACRMSB_ATTENUATION,
+		0, 511, 1, dac_tlv),
+};
+
 static const struct snd_soc_dapm_widget wm8741_dapm_widgets[] = {
 SND_SOC_DAPM_DAC("DACL", "Playback", SND_SOC_NOPM, 0, 0),
 SND_SOC_DAPM_DAC("DACR", "Playback", SND_SOC_NOPM, 0, 0),
@@ -398,7 +413,7 @@  static struct snd_soc_dai_driver wm8741_dai = {
 	.name = "wm8741",
 	.playback = {
 		.stream_name = "Playback",
-		.channels_min = 2,  /* Mono modes not yet supported */
+		.channels_min = 1,
 		.channels_max = 2,
 		.rates = WM8741_RATES,
 		.formats = WM8741_FORMATS,
@@ -416,6 +431,65 @@  static int wm8741_resume(struct snd_soc_codec *codec)
 #define wm8741_resume NULL
 #endif
 
+static int wm8741_configure(struct snd_soc_codec *codec)
+{
+	struct wm8741_priv *wm8741 = snd_soc_codec_get_drvdata(codec);
+
+	/* Configure differential mode */
+	switch (wm8741->pdata.diff_mode) {
+	case WM8741_DIFF_MODE_STEREO:
+	case WM8741_DIFF_MODE_STEREO_REVERSED:
+	case WM8741_DIFF_MODE_MONO_LEFT:
+	case WM8741_DIFF_MODE_MONO_RIGHT:
+		snd_soc_update_bits(codec, WM8741_MODE_CONTROL_2,
+				WM8741_DIFF_MASK,
+				wm8741->pdata.diff_mode << WM8741_DIFF_SHIFT);
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	/* Change some default settings - latch VU */
+	snd_soc_update_bits(codec, WM8741_DACLLSB_ATTENUATION,
+		WM8741_UPDATELL, WM8741_UPDATELL);
+	snd_soc_update_bits(codec, WM8741_DACLMSB_ATTENUATION,
+		WM8741_UPDATELM, WM8741_UPDATELM);
+	snd_soc_update_bits(codec, WM8741_DACRLSB_ATTENUATION,
+		WM8741_UPDATERL, WM8741_UPDATERL);
+	snd_soc_update_bits(codec, WM8741_DACRMSB_ATTENUATION,
+		WM8741_UPDATERM, WM8741_UPDATERM);
+
+	return 0;
+}
+
+static int wm8741_add_controls(struct snd_soc_codec *codec)
+{
+	struct wm8741_priv *wm8741 = snd_soc_codec_get_drvdata(codec);
+
+	switch (wm8741->pdata.diff_mode) {
+	case WM8741_DIFF_MODE_STEREO:
+	case WM8741_DIFF_MODE_STEREO_REVERSED:
+		snd_soc_add_codec_controls(codec,
+			wm8741_snd_controls_stereo,
+			ARRAY_SIZE(wm8741_snd_controls_stereo));
+		break;
+	case WM8741_DIFF_MODE_MONO_LEFT:
+		snd_soc_add_codec_controls(codec,
+			wm8741_snd_controls_mono_left,
+			ARRAY_SIZE(wm8741_snd_controls_mono_left));
+		break;
+	case WM8741_DIFF_MODE_MONO_RIGHT:
+		snd_soc_add_codec_controls(codec,
+			wm8741_snd_controls_mono_right,
+			ARRAY_SIZE(wm8741_snd_controls_mono_right));
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
 static int wm8741_probe(struct snd_soc_codec *codec)
 {
 	struct wm8741_priv *wm8741 = snd_soc_codec_get_drvdata(codec);
@@ -434,15 +508,17 @@  static int wm8741_probe(struct snd_soc_codec *codec)
 		goto err_enable;
 	}
 
-	/* Change some default settings - latch VU */
-	snd_soc_update_bits(codec, WM8741_DACLLSB_ATTENUATION,
-			    WM8741_UPDATELL, WM8741_UPDATELL);
-	snd_soc_update_bits(codec, WM8741_DACLMSB_ATTENUATION,
-			    WM8741_UPDATELM, WM8741_UPDATELM);
-	snd_soc_update_bits(codec, WM8741_DACRLSB_ATTENUATION,
-			    WM8741_UPDATERL, WM8741_UPDATERL);
-	snd_soc_update_bits(codec, WM8741_DACRMSB_ATTENUATION,
-			    WM8741_UPDATERM, WM8741_UPDATERM);
+	ret = wm8741_configure(codec);
+	if (ret < 0) {
+		dev_err(codec->dev, "Failed to change default settings\n");
+		goto err_enable;
+	}
+
+	ret = wm8741_add_controls(codec);
+	if (ret < 0) {
+		dev_err(codec->dev, "Failed to add controls\n");
+		goto err_enable;
+	}
 
 	dev_dbg(codec->dev, "Successful registration\n");
 	return ret;
@@ -467,8 +543,6 @@  static struct snd_soc_codec_driver soc_codec_dev_wm8741 = {
 	.remove =	wm8741_remove,
 	.resume =	wm8741_resume,
 
-	.controls = wm8741_snd_controls,
-	.num_controls = ARRAY_SIZE(wm8741_snd_controls),
 	.dapm_widgets = wm8741_dapm_widgets,
 	.num_dapm_widgets = ARRAY_SIZE(wm8741_dapm_widgets),
 	.dapm_routes = wm8741_dapm_routes,
@@ -493,6 +567,23 @@  static const struct regmap_config wm8741_regmap = {
 	.readable_reg = wm8741_readable,
 };
 
+static int wm8741_set_pdata(struct device *dev, struct wm8741_priv *wm8741)
+{
+	const struct wm8741_platform_data *pdata = dev_get_platdata(dev);
+	u32 diff_mode;
+
+	if (dev->of_node) {
+		if (of_property_read_u32(dev->of_node, "diff-mode", &diff_mode)
+				>= 0)
+			wm8741->pdata.diff_mode = diff_mode;
+	} else {
+		if (pdata != NULL)
+			memcpy(&wm8741->pdata, pdata, sizeof(wm8741->pdata));
+	}
+
+	return 0;
+}
+
 #if IS_ENABLED(CONFIG_I2C)
 static int wm8741_i2c_probe(struct i2c_client *i2c,
 			    const struct i2c_device_id *id)
@@ -522,6 +613,12 @@  static int wm8741_i2c_probe(struct i2c_client *i2c,
 		return ret;
 	}
 
+	wm8741_set_pdata(&i2c->dev, wm8741);
+	if (ret != 0) {
+		dev_err(&i2c->dev, "Failed to set pdata: %d\n", ret);
+		return ret;
+	}
+
 	i2c_set_clientdata(i2c, wm8741);
 
 	ret = snd_soc_register_codec(&i2c->dev,
@@ -582,6 +679,12 @@  static int wm8741_spi_probe(struct spi_device *spi)
 		return ret;
 	}
 
+	wm8741_set_pdata(&spi->dev, wm8741);
+	if (ret != 0) {
+		dev_err(&spi->dev, "Failed to set pdata: %d\n", ret);
+		return ret;
+	}
+
 	spi_set_drvdata(spi, wm8741);
 
 	ret = snd_soc_register_codec(&spi->dev,
diff --git a/sound/soc/codecs/wm8741.h b/sound/soc/codecs/wm8741.h
index 56c1b1d..c8835f6 100644
--- a/sound/soc/codecs/wm8741.h
+++ b/sound/soc/codecs/wm8741.h
@@ -194,6 +194,12 @@ 
 #define WM8741_DITHER_SHIFT                          0  /* DITHER - [1:0] */
 #define WM8741_DITHER_WIDTH                          2  /* DITHER - [1:0] */
 
+/* DIFF field values */
+#define WM8741_DIFF_MODE_STEREO                      0  /* stereo normal */
+#define WM8741_DIFF_MODE_STEREO_REVERSED             2  /* stereo reversed */
+#define WM8741_DIFF_MODE_MONO_LEFT                   1  /* mono left */
+#define WM8741_DIFF_MODE_MONO_RIGHT                  3  /* mono right */
+
 /*
  * R32 (0x20) - ADDITONAL_CONTROL_1
  */
@@ -208,4 +214,8 @@ 
 
 #define  WM8741_SYSCLK 0
 
+struct wm8741_platform_data {
+	u32 diff_mode;   /* Differential Output Mode */
+};
+
 #endif