ASoC: bcm2835: fix hw_params error when device is in prepared state

If bcm2835 is configured as bitclock master calling hw_params()
after prepare() fails with EBUSY. This also makes it impossible to
use bcm2835 in full duplex mode.

The error is caused by the split clock setup: clk_set_rate
is called in hw_params, clk_prepare_enable in prepare. As hw_params
doesn't check if the clock was already enabled clk_set_rate
fails with EBUSY.

Fix this by moving clock startup from prepare to hw_params and
let hw_params properly deal with an already set up or enabled
clock.
Signed-off-by: Matthias Reichl <hias@horus.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

sound/soc/bcm/bcm2835-i2s.c

@@ -130,6 +130,7 @@ struct bcm2835_i2s_dev {
 	struct regmap				*i2s_regmap;
 	struct clk				*clk;
 	bool					clk_prepared;
+	int					clk_rate;
 };
 
 static void bcm2835_i2s_start_clock(struct bcm2835_i2s_dev *dev)
@@ -419,10 +420,19 @@ static int bcm2835_i2s_hw_params(struct snd_pcm_substream *substream,
 	}
 
 	/* Clock should only be set up here if CPU is clock master */
-	if (bit_clock_master) {
-		ret = clk_set_rate(dev->clk, bclk_rate);
-		if (ret)
-			return ret;
+	if (bit_clock_master &&
+	    (!dev->clk_prepared || dev->clk_rate != bclk_rate)) {
+		if (dev->clk_prepared)
+			bcm2835_i2s_stop_clock(dev);
+
+		if (dev->clk_rate != bclk_rate) {
+			ret = clk_set_rate(dev->clk, bclk_rate);
+			if (ret)
+				return ret;
+			dev->clk_rate = bclk_rate;
+		}
+
+		bcm2835_i2s_start_clock(dev);
 	}
 
 	/* Setup the frame format */
@@ -618,8 +628,6 @@ static int bcm2835_i2s_prepare(struct snd_pcm_substream *substream,
 	struct bcm2835_i2s_dev *dev = snd_soc_dai_get_drvdata(dai);
 	uint32_t cs_reg;
 
-	bcm2835_i2s_start_clock(dev);
-
 	/*
 	 * Clear both FIFOs if the one that should be started
 	 * is not empty at the moment. This should only happen