On 01/19/2016 05:54 PM, Russell King - ARM Linux wrote:
> On Tue, Jan 19, 2016 at 02:40:31PM +0100, Arnaud Pouliquen wrote:
>> From: Moise Gergaud <moise.gergaud@xxxxxx>
>>
>> Add helper function to compute HDMI CTS and N parameters
>> Implementation is based on HDMI 1.4b specification.
>
> You should note that these CTS/N parameters are for where the audio and
> video clocks are coherent: iow, they are derived from the same source.
> If they can drift (because they're generated from different sources)
> then a hardware implementation which automatically calculates CTS is
> needed.
Yes this is the case on STI platform, CTS is computed by hardware. In
this case hdmi driver only takes into account the N value.
>
> However, some of the values given in the HDMI specs for CTS are actually
> two values, because a single value does not specify the audio clock even
> with the N values given. For these, the values returned will not give
> an accurate clock - this should also be noted.
In HDMI specs i only see a double value for 32 kHz with TMDS clock at
74.324 MHz. I can add a alt_CTS params in hdmi_audio_n_cts that will
be not null if alternate a value is needed. Is this something reasonable
for you?
As also suggest Mark, i need to add all the restriction info in code.
>
> Next, does "pixel clock" make sense when you have pixel repetition?
> Would calling this "tdms_clock" be more accurate to the specification
> and less mis-leading to users?
>
>> Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@xxxxxx>
>> ---
>> drivers/video/hdmi.c | 146 +++++++++++++++++++++++++++++++++++++++++++++++++++
>> include/linux/hdmi.h | 11 ++++
>> 2 files changed, 157 insertions(+)
>>
>> diff --git a/drivers/video/hdmi.c b/drivers/video/hdmi.c
>> index 1626892..8af33c1 100644
>> --- a/drivers/video/hdmi.c
>> +++ b/drivers/video/hdmi.c
>> @@ -1242,3 +1242,149 @@ 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 long pixel_clk;
>> + struct hdmi_audio_n_cts n_cts;
>> +};
>> +
>> +static const struct hdmi_audio_acr hdmi_audio_standard_acr[3][12] = {
>> + { /*32 kHz*/
>> + { 25175, { 4576, 28125 } }, /* 25,20/1.001 MHz */
>> + { 25200, { 4096, 25200 } }, /* 25.20 MHz */
>> + { 27000, { 4096, 27000 } }, /* 27.00 MHz */
>> + { 27027, { 4096, 27027 } }, /* 27.00*1.001 MHz */
>> + { 54000, { 4096, 54000 } }, /* 54.00 MHz */
>> + { 54054, { 4096, 54054 } }, /* 54.00*1.001 MHz */
>> + { 74176, { 11648, 310938 } }, /* 74.25/1.001 MHz */
>> + { 74250, { 4096, 74250 } }, /* 74.25 MHz */
>> + { 148352, { 11648, 421875 } }, /* 148.50/1.001 MHz */
>> + { 148500, { 4096, 148500 } }, /* 148.50 MHz */
>> + { 296703, { 5824, 421875 } }, /* 297/1.001 MHz */
>> + { 297000, { 3072, 222750 } }, /* 297 MHz */
>> + },
>> + { /*44.1 kHz, 88.2 kHz 176.4 kHz*/
>> + { 25175, { 7007, 31250 } }, /* 25,20/1.001 MHz */
>> + { 25200, { 6272, 28000 } }, /* 25.20 MHz */
>> + { 27000, { 6272, 30000 } }, /* 27.00 MHz */
>> + { 27027, { 6272, 30030 } }, /* 27.00*1.001 MHz */
>> + { 54000, { 6272, 60000 } }, /* 54.00 MHz */
>> + { 54054, { 6272, 60060 } }, /* 54.00*1.001 MHz */
>> + { 74176, { 17836, 234375 } }, /* 74.25/1.001 MHz */
>> + { 74250, { 6272, 82500 } }, /* 74.25 MHz */
>> + { 148352, { 8918, 234375 } }, /* 148.50/1.001 MHz */
>> + { 148500, { 6272, 165000 } }, /* 148.50 MHz */
>> + { 296703, { 4459, 234375 } }, /* 297/1.001 MHz */
>> + { 297000, { 4704, 247500 } }, /* 297 MHz */
>> + },
>> + { /*48 kHz, 96 kHz 192 kHz*/
>> + { 25175, { 6864, 28125 } }, /* 25,20/1.001 MHz */
>> + { 25200, { 6144, 25200 } }, /* 25.20 MHz */
>> + { 27000, { 6144, 27000 } }, /* 27.00 MHz */
>> + { 27027, { 6144, 27027 } }, /* 27.00*1.001 MHz */
>> + { 54000, { 6144, 54000 } }, /* 54.00 MHz */
>> + { 54054, { 6144, 54054 } }, /* 54.00*1.001 MHz */
>> + { 74176, { 11648, 140625 } }, /* 74.25/1.001 MHz */
>> + { 74250, { 6144, 74250 } }, /* 74.25 MHz */
>> + { 148352, { 5824, 140625 } }, /* 148.50/1.001 MHz */
>> + { 148500, { 6144, 148500 } }, /* 148.50 MHz */
>> + { 296703, { 5824, 281250 } }, /* 297/1.001 MHz */
>> + { 297000, { 5120, 247500 } }, /* 297 MHz */
>> + }
>> +};
>> +
>> +/**
>> + * hdmi_compute_n_cts() - compute N and CTS parameters
>> + * @audio_fs: audio frame clock frequency in kHz
>
> This is wrong. You're expecting values such as 32000 here. 32000kHz
> would be 32MHz, which is way too high for an audio frame clock. I
> think you mean Hz.
>
Oops, yes Hz not kHz
>> + * @pixel_clk: pixel clock frequency in kHz
>
> This is correct though.
>
>> + * @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_compute_n_cts(unsigned int audio_fs, unsigned long pixel_clk,
>> + struct hdmi_audio_n_cts *n_cts)
>> +{
>> + int audio_freq_id, i;
>> + int ratio = 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;
>> + ratio = 2;
>> + n_cts->n = 6272 * 2;
>> + break;
>> +
>> + case 96000:
>> + audio_freq_id = HDMI_AUDIO_N_CTS_48KHZ;
>> + ratio = 2;
>> + n_cts->n = 6144 * 2;
>> + break;
>> +
>> + case 176400:
>> + audio_freq_id = HDMI_AUDIO_N_CTS_44_1KHZ;
>> + ratio = 4;
>> + n_cts->n = 6272 * 4;
>> + break;
>> +
>> + case 192000:
>> + audio_freq_id = HDMI_AUDIO_N_CTS_48KHZ;
>> + ratio = 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 (pixel_clk == acr_table[i].pixel_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)
>> + */
>> + n_cts->cts = pixel_clk * n_cts->n / (128 * audio_fs);
>
> This looks like it could overflow. 192kHz audio clock, 297MHz tdms
> clock -> (297000 * 6144 * 4) = 7299072000. 32 bit unsigned math
> overflows beyond 4294967295.
>
Yes, need to use intermediate 64 bits variable for calculation
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