[alsa-devel] [RFC v2 1/6] video: hdmi: add helper function for N and CTS

Arnaud Pouliquen arnaud.pouliquen at st.com
Fri Jan 22 18:48:27 CET 2016


From: Moise Gergaud <moise.gergaud at st.com>

Add helper function to compute HDMI CTS and N parameters.
Implementation is based on HDMI 1.4b specification.

Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen at st.com>
---
 drivers/video/hdmi.c | 222 +++++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/hdmi.h |  22 +++++
 2 files changed, 244 insertions(+)

diff --git a/drivers/video/hdmi.c b/drivers/video/hdmi.c
index 1626892..be8b8ed 100644
--- a/drivers/video/hdmi.c
+++ b/drivers/video/hdmi.c
@@ -1242,3 +1242,225 @@ int hdmi_infoframe_unpack(union hdmi_infoframe *frame, void *buffer)
 	return ret;
 }
 EXPORT_SYMBOL(hdmi_infoframe_unpack);
+
+/**
+ * audio clock regeneration (acr) parameters
+ * N and CTS computation are based on HDMI specification 1.4b
+ */
+enum audio_rate {
+	HDMI_AUDIO_N_CTS_32KHZ,
+	HDMI_AUDIO_N_CTS_44_1KHZ,
+	HDMI_AUDIO_N_CTS_48KHZ,
+};
+
+struct hdmi_audio_acr {
+	unsigned int tmds_clk;
+	struct hdmi_audio_n_cts n_cts;
+};
+
+static const struct hdmi_audio_acr hdmi_audio_standard_acr[3][12] = {
+	{ /*32 kHz*/
+		{  25174825, {  4576,  28125, 0 } }, /* 25,20/1.001  MHz */
+		{  25200000, {  4096,  25200, 0 } }, /* 25.20        MHz */
+		{  27000000, {  4096,  27000, 0 } }, /* 27.00        MHz */
+		{  27027000, {  4096,  27027, 0 } }, /* 27.00*1.001  MHz */
+		{  54000000, {  4096,  54000, 0 } }, /* 54.00        MHz */
+		{  54054000, {  4096,  54054, 0 } }, /* 54.00*1.001  MHz */
+		{  74175824, { 11648, 210937, 50 } }, /* 74.25/1.001  MHz */
+		{  74250000, {  4096,  74250, 0 } }, /* 74.25        MHz */
+		{ 148351648, { 11648, 421875, 0 } }, /* 148.50/1.001 MHz */
+		{ 148500000, {  4096, 148500, 0 } }, /* 148.50       MHz */
+		{ 296703296, {  5824, 421875, 0 } }, /* 297/1.001    MHz */
+		{ 297000000, {  3072, 222750, 0 } }, /* 297          MHz */
+	},
+	{ /*44.1 kHz, 88.2 kHz  176.4 kHz*/
+		{  25174825, {  7007,  31250, 0 } }, /* 25,20/1.001  MHz */
+		{  25200000, {  6272,  28000, 0 } }, /* 25.20        MHz */
+		{  27000000, {  6272,  30000, 0 } }, /* 27.00        MHz */
+		{  27027000, {  6272,  30030, 0 } }, /* 27.00*1.001  MHz */
+		{  54000000, {  6272,  60000, 0 } }, /* 54.00        MHz */
+		{  54054000, {  6272,  60060, 0 } }, /* 54.00*1.001  MHz */
+		{  74175824, { 17836, 234375, 0 } }, /* 74.25/1.001  MHz */
+		{  74250000, {  6272,  82500, 0 } }, /* 74.25        MHz */
+		{ 148351648, {  8918, 234375, 0 } }, /* 148.50/1.001 MHz */
+		{ 148500000, {  6272, 165000, 0 } }, /* 148.50       MHz */
+		{ 296703296, {  4459, 234375, 0 } }, /* 297/1.001    MHz */
+		{ 297000000, {  4704, 247500, 0 } }, /* 297          MHz */
+	},
+	{ /*48 kHz, 96 kHz  192 kHz*/
+		{  25174825, {  6864,  28125, 0 } }, /* 25,20/1.001  MHz */
+		{  25200000, {  6144,  25200, 0 } }, /* 25.20        MHz */
+		{  27000000, {  6144,  27000, 0 } }, /* 27.00        MHz */
+		{  27027000, {  6144,  27027, 0 } }, /* 27.00*1.001  MHz */
+		{  54000000, {  6144,  54000, 0 } }, /* 54.00        MHz */
+		{  54054000, {  6144,  54054, 0 } }, /* 54.00*1.001  MHz */
+		{  74175824, { 11648, 140625, 0 } }, /* 74.25/1.001  MHz */
+		{  74250000, {  6144,  74250, 0 } }, /* 74.25        MHz */
+		{ 148351648, {  5824, 140625, 0 } }, /* 148.50/1.001 MHz */
+		{ 148500000, {  6144, 148500, 0 } }, /* 148.50       MHz */
+		{ 296703296, {  5824, 281250, 0 } }, /* 297/1.001    MHz */
+		{ 297000000, {  5120, 247500, 0 } }, /* 297          MHz */
+	}
+};
+
+/**
+ * hdmi_audio_get_coherent_n_cts() - compute N and CTS parameters for coherent
+ * clocks. Coherent clock means that audio and TMDS clocks have the same
+ * source (no drifts between clocks).
+ *
+ * @audio_fs: audio frame clock frequency in Hz
+ * @tmds_clk: HDMI TMDS clock frequency in Hz
+ * @n_cts: N and CTS parameter returned to user
+ *
+ * Values computed are based on table described in HDMI specification 1.4b
+ *
+ * Returns 0 on success or a negative error code on failure.
+ */
+int hdmi_audio_get_coherent_n_cts(unsigned int audio_fs,
+				  unsigned int tmds_clk,
+				  struct hdmi_audio_n_cts *n_cts)
+{
+	int audio_freq_id, i;
+	int rate_coeff = 1;
+	const struct hdmi_audio_acr  *acr_table;
+	const struct hdmi_audio_n_cts *predef_n_cts = NULL;
+
+	switch (audio_fs) {
+	case 32000:
+		audio_freq_id = HDMI_AUDIO_N_CTS_32KHZ;
+		n_cts->n = 4096;
+		break;
+
+	case 44100:
+		audio_freq_id = HDMI_AUDIO_N_CTS_44_1KHZ;
+		n_cts->n = 6272;
+		break;
+
+	case 48000:
+		audio_freq_id = HDMI_AUDIO_N_CTS_48KHZ;
+		n_cts->n = 6144;
+		break;
+
+	case 88200:
+		audio_freq_id = HDMI_AUDIO_N_CTS_44_1KHZ;
+		rate_coeff = 2;
+		n_cts->n = 6272 * 2;
+		break;
+
+	case 96000:
+		audio_freq_id = HDMI_AUDIO_N_CTS_48KHZ;
+		rate_coeff = 2;
+		n_cts->n = 6144 * 2;
+		break;
+
+	case 176400:
+		audio_freq_id = HDMI_AUDIO_N_CTS_44_1KHZ;
+		rate_coeff = 4;
+		n_cts->n = 6272 * 4;
+		break;
+
+	case 192000:
+		audio_freq_id = HDMI_AUDIO_N_CTS_48KHZ;
+		rate_coeff = 4;
+		n_cts->n = 6144 * 4;
+		break;
+
+	default:
+		return -EINVAL;
+	}
+
+	acr_table = hdmi_audio_standard_acr[audio_freq_id];
+	for (i = 0; i < ARRAY_SIZE(hdmi_audio_standard_acr[0]); i++) {
+		if (tmds_clk == acr_table[i].tmds_clk) {
+			predef_n_cts = &acr_table[i].n_cts;
+			break;
+		}
+	}
+
+	if (!predef_n_cts) {
+		/*
+		 * predefined frequency not found. Compute CTS using formula:
+		 * CTS = (Ftdms_clk * N) / (128* audio_fs)
+		 */
+		uint64_t val, min;
+
+		val = (uint64_t)tmds_clk * n_cts->n;
+
+		n_cts->cts = div64_u64(val, 128UL * audio_fs);
+		min = (uint64_t)n_cts->cts * 128UL * audio_fs;
+		if (min < (val)) {
+			/*
+			 * non-accurate value for CTS
+			 * compute ratio, needed by user to alternate in ACR
+			 * between CTS and CTS + 1 value.
+			 */
+			n_cts->cts_1_ratio = ((int32_t)(val - min)) * 100 /
+					     (128 * audio_fs);
+			n_cts->cts_1_ratio = 100 - n_cts->cts_1_ratio;
+		} else {
+			n_cts->cts_1_ratio = 0;
+		}
+	} else {
+		n_cts->n = predef_n_cts->n * rate_coeff;
+		n_cts->cts = predef_n_cts->cts;
+		n_cts->cts_1_ratio = predef_n_cts->cts_1_ratio;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(hdmi_audio_get_coherent_n_cts);
+
+/**
+ * hdmi_audio_get_non_coherent_n() - get N parameter for non-coherent
+ * clocks. None-coherent clocks means that audio and TMDS clocks have not the
+ * same source (drifts between clocks). In this case assumption is that CTS is
+ * automatically calculated by hardware.
+ *
+ * @audio_fs: audio frame clock frequency in Hz
+ *
+ * Values computed are based on table described in HDMI specification 1.4b
+ *
+ * Returns n value.
+ */
+int hdmi_audio_get_non_coherent_n(unsigned int audio_fs)
+{
+	unsigned int n;
+
+	switch (audio_fs) {
+	case 32000:
+		n = 4096;
+		break;
+
+	case 44100:
+		n = 6272;
+		break;
+
+	case 48000:
+		n = 6144;
+		break;
+
+	case 88200:
+		n = 6272 * 2;
+		break;
+
+	case 96000:
+		n = 6144 * 2;
+		break;
+
+	case 176400:
+		n = 6272 * 4;
+		break;
+
+	case 192000:
+		n = 6144 * 4;
+		break;
+
+	default:
+		/* Not pre-defined, recommended value: 128 * fs / 1000 */
+		n = (audio_fs * 128) / 1000;
+	}
+
+	return n;
+}
+EXPORT_SYMBOL(hdmi_audio_get_non_coherent_n);
+
diff --git a/include/linux/hdmi.h b/include/linux/hdmi.h
index e974420..bf5c136 100644
--- a/include/linux/hdmi.h
+++ b/include/linux/hdmi.h
@@ -333,4 +333,26 @@ int hdmi_infoframe_unpack(union hdmi_infoframe *frame, void *buffer);
 void hdmi_infoframe_log(const char *level, struct device *dev,
 			union hdmi_infoframe *frame);
 
+/**
+ * struct hdmi_audio_n_cts - n and cts parameter for ACR packets
+ * @n: N parameter
+ * @cts: CTS parameter
+ * @cts_1_ratio: ratio from 0 to 99 to alternate "CTS" and "CTS + 1" values
+ *  ratio = 0: CTS parameter is accurate, no need to alternate with "CTS + 1"
+ *             value
+ *  ratio = x: Need to alternate in ACR "CTS + 1" value x% of the time to
+ *             generate accurate audio clock
+ */
+struct hdmi_audio_n_cts {
+	unsigned int n;
+	unsigned int cts;
+	unsigned int cts_1_ratio;
+};
+
+int hdmi_audio_get_coherent_n_cts(unsigned int audio_fs,
+				  unsigned int tmds_clk,
+				  struct hdmi_audio_n_cts *n_cts);
+
+int hdmi_audio_get_non_coherent_n(unsigned int audio_fs);
+
 #endif /* _DRM_HDMI_H */
-- 
1.9.1



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