[PATCH v3 1/2] video: hdmi: add helper function for N and CTS
Philipp Zabel
p.zabel at pengutronix.de
Thu Apr 21 12:39:28 UTC 2016
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?
> + { 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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