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@st.com
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@st.com
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