ASoC: ti: davinci-i2s: Use external clock to drive sample rate generator

McBSP's internal sample rate generator can be programed to be driven by
its internal clock or by an external clock source located on CLKS pin.
The external clock source case is not handled by the driver.

Handle an optional clock related to this external clock source. If
present, the driver uses the clock located on CLKS pin as input for the
sample rate generator. Thus, the external clock rate is used to compute
divisors. If this optional clock is not present, the sample rate
generator is driven by the McBSP's functional clock.
Signed-off-by: Bastien Curutchet <bastien.curutchet@bootlin.com>
Acked-by: Peter Ujfalusi <peter.ujfalusi@gmail.com>
Link: https://msgid.link/r/20240402071213.11671-6-bastien.curutchet@bootlin.comSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/ti/davinci-i2s.c

@@ -134,6 +134,7 @@ struct davinci_mcbsp_dev {
 	int				mode;
 	u32				pcr;
 	struct clk			*clk;
+	struct clk			*ext_clk;
 	/*
 	 * Combining both channels into 1 element will at least double the
 	 * amount of time between servicing the dma channel, increase
@@ -364,7 +365,8 @@ static int davinci_i2s_hw_params(struct snd_pcm_substream *substream,
 	struct davinci_mcbsp_dev *dev = snd_soc_dai_get_drvdata(dai);
 	struct snd_interval *i = NULL;
 	int mcbsp_word_length, master;
-	unsigned int rcr, xcr, srgr, clk_div, freq, framesize;
+	unsigned int rcr, xcr, clk_div, freq, framesize;
+	unsigned int srgr = 0;
 	u32 spcr;
 	snd_pcm_format_t fmt;
 	unsigned element_cnt = 1;
@@ -385,9 +387,13 @@ static int davinci_i2s_hw_params(struct snd_pcm_substream *substream,
 
 	switch (master) {
 	case SND_SOC_DAIFMT_BP_FP:
-		freq = clk_get_rate(dev->clk);
-		srgr = DAVINCI_MCBSP_SRGR_FSGM |
-		       DAVINCI_MCBSP_SRGR_CLKSM;
+		if (dev->ext_clk) {
+			freq = clk_get_rate(dev->ext_clk);
+		} else {
+			freq = clk_get_rate(dev->clk);
+			srgr = DAVINCI_MCBSP_SRGR_CLKSM;
+		}
+		srgr |= DAVINCI_MCBSP_SRGR_FSGM;
 		srgr |= DAVINCI_MCBSP_SRGR_FWID(mcbsp_word_length *
 						8 - 1);
 		if (dev->i2s_accurate_sck) {
@@ -691,12 +697,36 @@ static int davinci_i2s_probe(struct platform_device *pdev)
 		return -ENODEV;
 	}
 
-	dev->clk = clk_get(&pdev->dev, NULL);
+	/*
+	 * The optional is there for backward compatibility.
+	 * If 'fck' is not present, the clk_get(dev, NULL) that follows may find something
+	 */
+	dev->clk = devm_clk_get_optional(&pdev->dev, "fck");
 	if (IS_ERR(dev->clk))
-		return -ENODEV;
-	ret = clk_enable(dev->clk);
+		return dev_err_probe(&pdev->dev, PTR_ERR(dev->clk), "Invalid functional clock\n");
+	if (!dev->clk) {
+		dev->clk = devm_clk_get(&pdev->dev, NULL);
+		if (IS_ERR(dev->clk))
+			return dev_err_probe(&pdev->dev, PTR_ERR(dev->clk),
+					     "Missing functional clock\n");
+	}
+
+	dev->ext_clk = devm_clk_get_optional(&pdev->dev, "clks");
+	if (IS_ERR(dev->ext_clk))
+		return dev_err_probe(&pdev->dev, PTR_ERR(dev->ext_clk), "Invalid external clock\n");
+
+	ret = clk_prepare_enable(dev->clk);
 	if (ret)
-		goto err_put_clk;
+		return ret;
+
+	if (dev->ext_clk) {
+		dev_dbg(&pdev->dev, "External clock used for sample rate generator\n");
+		ret = clk_prepare_enable(dev->ext_clk);
+		if (ret) {
+			dev_err_probe(&pdev->dev, ret, "Failed to enable external clock\n");
+			goto err_disable_clk;
+		}
+	}
 
 	dev->dev = &pdev->dev;
 	dev_set_drvdata(&pdev->dev, dev);
@@ -704,7 +734,7 @@ static int davinci_i2s_probe(struct platform_device *pdev)
 	ret = snd_soc_register_component(&pdev->dev, &davinci_i2s_component,
 					 &davinci_i2s_dai, 1);
 	if (ret != 0)
-		goto err_release_clk;
+		goto err_disable_ext_clk;
 
 	ret = edma_pcm_platform_register(&pdev->dev);
 	if (ret) {
@@ -716,10 +746,12 @@ static int davinci_i2s_probe(struct platform_device *pdev)
 
 err_unregister_component:
 	snd_soc_unregister_component(&pdev->dev);
-err_release_clk:
-	clk_disable(dev->clk);
-err_put_clk:
-	clk_put(dev->clk);
+err_disable_ext_clk:
+	if (dev->ext_clk)
+		clk_disable_unprepare(dev->ext_clk);
+err_disable_clk:
+	clk_disable_unprepare(dev->clk);
+
 	return ret;
 }
 
@@ -729,9 +761,10 @@ static void davinci_i2s_remove(struct platform_device *pdev)
 
 	snd_soc_unregister_component(&pdev->dev);
 
-	clk_disable(dev->clk);
-	clk_put(dev->clk);
-	dev->clk = NULL;
+	clk_disable_unprepare(dev->clk);
+
+	if (dev->ext_clk)
+		clk_disable_unprepare(dev->ext_clk);
 }
 
 static const struct of_device_id davinci_i2s_match[] __maybe_unused = {