linux-kernel - [PATCH v5 10/11] ASoC: tegra20: spdif: Filter out unsupported rates

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Date:   Fri, 17 Dec 2021 20:56:05 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Mark Brown <broonie@...nel.org>, Takashi Iwai <tiwai@...e.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Liam Girdwood <lgirdwood@...il.com>,
        Agneli <poczt@...tonmail.ch>
Cc:     linux-tegra@...r.kernel.org, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: [PATCH v5 10/11] ASoC: tegra20: spdif: Filter out unsupported rates

SPDIF and other SoC components share audio PLL on Tegra, thus only one
component may set the desired base clock rate. This creates problem for
HDMI audio because it uses SPDIF and audio may not work if SPDIF's clock
doesn't exactly match standard audio rate since some receivers may reject
audio in that case. Filter out audio rates which SPDIF output can't
support, assuming that other components won't change rate at runtime.

Acked-by: Thierry Reding <treding@...dia.com>
Signed-off-by: Dmitry Osipenko <digetx@...il.com>
---
 sound/soc/tegra/tegra20_spdif.c | 63 ++++++++++++++++++++++++++++++++-
 1 file changed, 62 insertions(+), 1 deletion(-)

diff --git a/sound/soc/tegra/tegra20_spdif.c b/sound/soc/tegra/tegra20_spdif.c
index a4aa5614aef4..8cc114c1862f 100644
--- a/sound/soc/tegra/tegra20_spdif.c
+++ b/sound/soc/tegra/tegra20_spdif.c
@@ -78,7 +78,8 @@ static int tegra20_spdif_hw_params(struct snd_pcm_substream *substream,
 {
 	struct tegra20_spdif *spdif = dev_get_drvdata(dai->dev);
 	unsigned int mask = 0, val = 0;
-	int ret, spdifclock;
+	long rate, spdifclock;
+	int ret;
 
 	mask |= TEGRA20_SPDIF_CTRL_PACK |
 		TEGRA20_SPDIF_CTRL_BIT_MODE_MASK;
@@ -133,6 +134,12 @@ static int tegra20_spdif_hw_params(struct snd_pcm_substream *substream,
 		return ret;
 	}
 
+	rate = clk_get_rate(spdif->clk_spdif_out);
+	if (rate != spdifclock)
+		dev_warn_once(dai->dev,
+			      "SPDIF clock rate %ld doesn't match requested rate %ld\n",
+			      spdifclock, rate);
+
 	return 0;
 }
 
@@ -172,6 +179,59 @@ static int tegra20_spdif_trigger(struct snd_pcm_substream *substream, int cmd,
 	return 0;
 }
 
+static int tegra20_spdif_filter_rates(struct snd_pcm_hw_params *params,
+				      struct snd_pcm_hw_rule *rule)
+{
+	struct snd_interval *r = hw_param_interval(params, rule->var);
+	struct snd_soc_dai *dai = rule->private;
+	struct tegra20_spdif *spdif = dev_get_drvdata(dai->dev);
+	struct clk *parent = clk_get_parent(spdif->clk_spdif_out);
+	const unsigned int rates[] = { 32000, 44100, 48000 };
+	long i, parent_rate, valid_rates = 0;
+
+	parent_rate = clk_get_rate(parent);
+	if (parent_rate <= 0) {
+		dev_err(dai->dev, "Can't get parent clock rate: %ld\n",
+			parent_rate);
+		return parent_rate ?: -EINVAL;
+	}
+
+	for (i = 0; i < ARRAY_SIZE(rates); i++) {
+		if (parent_rate % (rates[i] * 128) == 0)
+			valid_rates |= BIT(i);
+	}
+
+	/*
+	 * At least one rate must be valid, otherwise the parent clock isn't
+	 * audio PLL. Nothing should be filtered in this case.
+	 */
+	if (!valid_rates)
+		valid_rates = BIT(ARRAY_SIZE(rates)) - 1;
+
+	return snd_interval_list(r, ARRAY_SIZE(rates), rates, valid_rates);
+}
+
+static int tegra20_spdif_startup(struct snd_pcm_substream *substream,
+				 struct snd_soc_dai *dai)
+{
+	if (!device_property_read_bool(dai->dev, "nvidia,fixed-parent-rate"))
+		return 0;
+
+	/*
+	 * SPDIF and I2S share audio PLL. HDMI takes audio packets from SPDIF
+	 * and audio may not work on some TVs if clock rate isn't precise.
+	 *
+	 * PLL rate is controlled by I2S side. Filter out audio rates that
+	 * don't match PLL rate at the start of stream to allow both SPDIF
+	 * and I2S work simultaneously, assuming that PLL rate won't be
+	 * changed later on.
+	 */
+	return snd_pcm_hw_rule_add(substream->runtime, 0,
+				   SNDRV_PCM_HW_PARAM_RATE,
+				   tegra20_spdif_filter_rates, dai,
+				   SNDRV_PCM_HW_PARAM_RATE, -1);
+}
+
 static int tegra20_spdif_probe(struct snd_soc_dai *dai)
 {
 	struct tegra20_spdif *spdif = dev_get_drvdata(dai->dev);
@@ -185,6 +245,7 @@ static int tegra20_spdif_probe(struct snd_soc_dai *dai)
 static const struct snd_soc_dai_ops tegra20_spdif_dai_ops = {
 	.hw_params = tegra20_spdif_hw_params,
 	.trigger = tegra20_spdif_trigger,
+	.startup = tegra20_spdif_startup,
 };
 
 static struct snd_soc_dai_driver tegra20_spdif_dai = {
-- 
2.33.1