ASoC: sta32x: Add support for XTI clock

The STA32x chips feature an XTI clock input that needs to be stable before
the reset signal is released. Therefore, the chip driver needs to get a
handle to the clock. Instead of relying on other parts of the system to
enable the clock, let the codec driver grab a handle itself.

In order to keep existing boards working, clock support is made optional.

Signed-off-by: Daniel Mack <[e-mail]>
Signed-off-by: Mark Brown <[e-mail]>

Documentation/devicetree/bindings/sound/st,sta32x.txt

···
 
 Optional properties:
 
+  - clocks, clock-names: Clock specifier for XTI input clock.
+	If specified, the clock will be enabled when the codec is probed,
+	and disabled when it is removed. The 'clock-names' must be set to 'xti'.
+
   -  st,output-conf: number, Selects the output configuration:
 	0: 2-channel (full-bridge) power, 2-channel data-out
 	1: 2 (half-bridge). 1 (full-bridge) on-board power
···
 codec: sta32x@38 {
 	compatible = "st,sta32x";
 	reg = <0x1c>;
+	clocks = <&clock>;
+	clock-names = "xti";
 	reset-gpios = <&gpio1 19 0>;
 	power-down-gpios = <&gpio1 16 0>;
 	st,output-conf = /bits/ 8  <0x3>;	// set output to 2-channel

sound/soc/codecs/sta32x.c

···
 #include <linux/module.h>
 #include <linux/moduleparam.h>
 #include <linux/init.h>
+#include <linux/clk.h>
 #include <linux/delay.h>
 #include <linux/pm.h>
 #include <linux/i2c.h>
···
 /* codec private data */
 struct sta32x_priv {
 	struct regmap *regmap;
+	struct clk *xti_clk;
 	struct regulator_bulk_data supplies[ARRAY_SIZE(sta32x_supply_names)];
 	struct snd_soc_component *component;
 	struct sta32x_platform_data *pdata;
···
 	struct sta32x_priv *sta32x = snd_soc_component_get_drvdata(component);
 	struct sta32x_platform_data *pdata = sta32x->pdata;
 	int i, ret = 0, thermal = 0;
+
+	sta32x->component = component;
+
+	if (sta32x->xti_clk) {
+		ret = clk_prepare_enable(sta32x->xti_clk);
+		if (ret != 0) {
+			dev_err(component->dev,
+				"Failed to enable clock: %d\n", ret);
+			return ret;
+		}
+	}
+
 	ret = regulator_bulk_enable(ARRAY_SIZE(sta32x->supplies),
 				    sta32x->supplies);
 	if (ret != 0) {
···
 
 	sta32x_watchdog_stop(sta32x);
 	regulator_bulk_disable(ARRAY_SIZE(sta32x->supplies), sta32x->supplies);
+
+	if (sta32x->xti_clk)
+		clk_disable_unprepare(sta32x->xti_clk);
 }
 
 static const struct snd_soc_component_driver sta32x_component = {
···
 			return ret;
 	}
 #endif
+
+	/* Clock */
+	sta32x->xti_clk = devm_clk_get(dev, "xti");
+	if (IS_ERR(sta32x->xti_clk)) {
+		ret = PTR_ERR(sta32x->xti_clk);
+
+		if (ret == -EPROBE_DEFER)
+			return ret;
+
+		sta32x->xti_clk = NULL;
+	}
 
 	/* GPIOs */
 	sta32x->gpiod_nreset = devm_gpiod_get_optional(dev, "reset",