Re: [PATCH v3 1/2] video: hdmi: add helper function for N and CTS

[Philipp Zabel <p.zabel@pengutronix.de>]

Hi Arnaud,

Am Donnerstag, den 21.04.2016, 10:07 +0200 schrieb Arnaud Pouliquen:
> 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@st.com>
> Acked-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
> Acked-by: Vincent ABRIOU <vincent.abriou@st.com>

Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>

> ---
>  drivers/video/hdmi.c | 202 +++++++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/hdmi.h |  22 ++++++
>  2 files changed, 224 insertions(+)
> 
> diff --git a/drivers/video/hdmi.c b/drivers/video/hdmi.c
> index 1626892..6381ce0 100644
> --- a/drivers/video/hdmi.c
> +++ b/drivers/video/hdmi.c
> @@ -1242,3 +1242,205 @@ 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*/

If you used

	[HDMI_AUDIO_N_CTS_32KHZ] = {

instead, that would mirror how the array is indexed via audio_freq_id in
hdmi_audio_get_coherent_n_cts below.

> +		{  25174825, {  4576,  28125, 0 } }, /* 25,20/1.001  MHz */
                                                           ^
s/,/./

> +		{  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 */
                           ^
Maybe add a comment above that tmds_clk is rounded down?

> +		{ 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;
> +	u64 val, min;
> +	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;
> +			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;
> +		}
> +	}
> +
> +	/*
> +	* predefined frequency not found. Compute CTS using formula:
         ^
> +	* CTS = (Ftdms_clk * N) / (128* audio_fs)
         ^                             ^
> +	*/
         ^
Missing spaces.

> +	val = (u64)tmds_clk * n_cts->n;
> +	n_cts->cts = div64_u64(val, 128UL * audio_fs);
> +
> +	n_cts->cts_1_ratio = 0;
> +	min = (u64)n_cts->cts * 128UL * audio_fs;
> +	if (min < (val)) {
                   ^   ^
These parentheses are not needed.

> +		/*
> +		* non-accurate value for CTS
                 ^
> +		* compute ratio, needed by user to alternate in ACR
                 ^
> +		* between CTS and CTS + 1 value.
                 ^
> +		*/
                 ^
Missing spaces.

> +		n_cts->cts_1_ratio = 100 - ((u32)(val - min)) * 100 /
> +					    (128 * audio_fs);

I don't understand the purpose of the (100-x) above (and how cts_1_ratio
is supposed to be used).

When for example val == (min + 0.3 * 128 * audio_fs) then
cts_1_ratio = 70.
To achieve an average CTS of (val), shouldn't (min) be used 70% of the
time and (min+1) be used 30% of the time?
I would have expected (cts_1_ratio == 30) in that case.

> +	}
> +
> +	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..28b6794 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 with ACR "CTS + 1" value x% of the time to
> + *             generate accurate audio clock

Does this mean that at cts_1_ratio == 30, CTS should be used 70% of the
time, and CTS+1 should be used 30% of the time, or the other way around?

> + */
> +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 */

regards
Philipp

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