[alsa-devel] [PATCH v3 1/2] video: hdmi: add helper function for N and CTS
Arnaud Pouliquen
arnaud.pouliquen at st.com
Thu Apr 21 15:52:24 CEST 2016
On 04/21/2016 02:39 PM, Philipp Zabel wrote:
> 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 at st.com>
>> Acked-by: Benjamin Gaignard <benjamin.gaignard at linaro.org>
>> Acked-by: Vincent ABRIOU <vincent.abriou at st.com>
>
> Reviewed-by: Philipp Zabel <p.zabel at 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?
My apologize, I have forgotten to add 296703297 value to take into
account truncated and rounded values as discussed in V2:
{ 296703296, { 5824, 421875, 0 } }, /* 297/1.001 MHz (truncated) */
{ 296703297, { 5824, 421875, 0 } }, /* 297/1.001 MHz (rounded) */
>
>> + { 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.
you are right! my reasoning is foolish... Thank for pointing this error!
>>
>> +/**
>> + * 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?
yes CTS should be used 70% of the time, i will add example in comment
>
>> + */
>> +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
>
thanks and Regards
Arnaud
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