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.
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.
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.
- @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.