ASoC: sun8i-codec: Protect the clock rate while streams are open

The codec's clock input is shared among all AIFs, and shared with other
audio-related hardware in the SoC, including I2S and SPDIF controllers.
To ensure sample rates selected by userspace or by codec2codec DAI links
are maintained, the clock rate must be protected while it is in use.
Signed-off-by: Samuel Holland <samuel@sholland.org>
Acked-by: Maxime Ripard <mripard@kernel.org>
Link: https://lore.kernel.org/r/20201014061941.4306-13-samuel@sholland.orgSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/sunxi/Kconfig

@@ -14,6 +14,7 @@ config SND_SUN8I_CODEC
 	tristate "Allwinner SUN8I audio codec"
 	depends on OF
 	depends on MACH_SUN8I || (ARM64 && ARCH_SUNXI) || COMPILE_TEST
+	select COMMON_CLK
 	select REGMAP_MMIO
 	help
 	  This option enables the digital part of the internal audio codec for

sound/soc/sunxi/sun8i-codec.c

@@ -421,6 +421,11 @@ static int sun8i_codec_get_lrck_div_order(unsigned int slots,
 	return order_base_2(div);
 }
 
+static unsigned int sun8i_codec_get_sysclk_rate(unsigned int sample_rate)
+{
+	return sample_rate % 4000 ? 22579200 : 24576000;
+}
+
 static int sun8i_codec_hw_params(struct snd_pcm_substream *substream,
 				 struct snd_pcm_hw_params *params,
 				 struct snd_soc_dai *dai)
@@ -430,8 +435,8 @@ static int sun8i_codec_hw_params(struct snd_pcm_substream *substream,
 	unsigned int sample_rate = params_rate(params);
 	unsigned int slots = aif->slots ?: params_channels(params);
 	unsigned int slot_width = aif->slot_width ?: params_width(params);
-	unsigned int sysclk_rate = clk_get_rate(scodec->clk_module);
-	int lrck_div_order, word_size;
+	unsigned int sysclk_rate = sun8i_codec_get_sysclk_rate(sample_rate);
+	int lrck_div_order, ret, word_size;
 	u8 bclk_div;
 
 	/* word size */
@@ -471,6 +476,24 @@ static int sun8i_codec_hw_params(struct snd_pcm_substream *substream,
 			   SUN8I_AIF1CLK_CTRL_AIF1_BCLK_DIV_MASK,
 			   bclk_div << SUN8I_AIF1CLK_CTRL_AIF1_BCLK_DIV);
 
+	/*
+	 * SYSCLK rate
+	 *
+	 * Clock rate protection is reference counted; but hw_params may be
+	 * called many times per substream, without matching calls to hw_free.
+	 * Protect the clock rate once per AIF, on the first hw_params call
+	 * for the first substream. clk_set_rate() will allow clock rate
+	 * changes on subsequent calls if only one AIF has open streams.
+	 */
+	ret = (aif->open_streams ? clk_set_rate : clk_set_rate_exclusive)(scodec->clk_module,
+									  sysclk_rate);
+	if (ret == -EBUSY)
+		dev_err(dai->dev,
+			"%s sample rate (%u Hz) conflicts with other audio streams\n",
+			dai->name, sample_rate);
+	if (ret < 0)
+		return ret;
+
 	if (!aif->open_streams)
 		scodec->sysclk_refcnt++;
 	scodec->sysclk_rate = sysclk_rate;
@@ -487,9 +510,11 @@ static int sun8i_codec_hw_free(struct snd_pcm_substream *substream,
 	struct sun8i_codec *scodec = snd_soc_dai_get_drvdata(dai);
 	struct sun8i_codec_aif *aif = &scodec->aifs[dai->id];
 
+	/* Drop references when the last substream for the AIF is freed. */
 	if (aif->open_streams != BIT(substream->stream))
 		goto done;
 
+	clk_rate_exclusive_put(scodec->clk_module);
 	scodec->sysclk_refcnt--;
 	aif->sample_rate = 0;