ASoC: pxa-ssp: add support for an external clock in devicetree

Allow setting a clock called 'extclk' in the device of the ssp-dai
device. If specified, this clock will be set to the mclk rate from the
DAI's .set_sysclk() callback. The DAI will also configure itself to
use that external clock.
Signed-off-by: Daniel Mack <daniel@zonque.org>
Signed-off-by: Mark Brown <broonie@kernel.org>

Documentation/devicetree/bindings/sound/mrvl,pxa-ssp.txt

@@ -5,6 +5,14 @@ Required properties:
 	compatible	Must be "mrvl,pxa-ssp-dai"
 	port		A phandle reference to a PXA ssp upstream device
 
+Optional properties:
+
+	clock-names
+	clocks		Through "clock-names" and "clocks", external clocks
+			can be configured. If a clock names "extclk" exists,
+			it will be set to the mclk rate of the audio stream
+			and be used as clock provider of the DAI.
+
 Example:
 
 	/* upstream device */

sound/soc/pxa/pxa-ssp.c

@@ -41,6 +41,7 @@
  */
 struct ssp_priv {
 	struct ssp_device *ssp;
+	struct clk *extclk;
 	unsigned long ssp_clk;
 	unsigned int sysclk;
 	unsigned int dai_fmt;
@@ -205,6 +206,21 @@ static int pxa_ssp_set_dai_sysclk(struct snd_soc_dai *cpu_dai,
 	u32 sscr0 = pxa_ssp_read_reg(ssp, SSCR0) &
 		~(SSCR0_ECS | SSCR0_NCS | SSCR0_MOD | SSCR0_ACS);
 
+	if (priv->extclk) {
+		int ret;
+
+		/*
+		 * For DT based boards, if an extclk is given, use it
+		 * here and configure PXA_SSP_CLK_EXT.
+		 */
+
+		ret = clk_set_rate(priv->extclk, freq);
+		if (ret < 0)
+			return ret;
+
+		clk_id = PXA_SSP_CLK_EXT;
+	}
+
 	dev_dbg(&ssp->pdev->dev,
 		"pxa_ssp_set_dai_sysclk id: %d, clk_id %d, freq %u\n",
 		cpu_dai->id, clk_id, freq);
@@ -774,6 +790,15 @@ static int pxa_ssp_probe(struct snd_soc_dai *dai)
 			ret = -ENODEV;
 			goto err_priv;
 		}
+
+		priv->extclk = devm_clk_get(dev, "extclk");
+		if (IS_ERR(priv->extclk)) {
+			ret = PTR_ERR(priv->extclk);
+			if (ret == -EPROBE_DEFER)
+				return ret;
+
+			priv->extclk = NULL;
+		}
 	} else {
 		priv->ssp = pxa_ssp_request(dai->id + 1, "SoC audio");
 		if (priv->ssp == NULL) {