At Tue, 18 Nov 2008 16:57:16 +0800, Wu Fengguang wrote:
To play a 3+ channels LPCM/DSD stream via HDMI,
- HDMI sink must tell HDMI source about its speaker placements (via ELD, speaker-allocation field)
- HDMI source must tell the HDMI sink about channel allocation (via audio infoframe, channel-allocation field)
(related docs: HDMI 1.3a spec section 7.4, CEA-861-D section 7.5.3 and 6.6)
This patch attempts to set the CA(channel-allocation) byte in the audio infoframe according to
- the number of channels in the current stream
- the speakers attached to the HDMI sink
A channel_allocations[] line must meet the following two criterions to be considered as a valid candidate for CA:
- its number of allocated channels = substream->runtime->channels
- its speakers are a subset of the available ones on the sink side
If there are multiple candidates, the first one is selected. This simple policy shall cheat the sink into playing music, but may direct data to the wrong speakers.
Sorry, this last step is not obvious to me. Any domain experts, please?
The problem is that the speaker positioning isn't defined in the ALSA API yet. I think your implementation will work in practice.
+static struct cea_channel_speaker_allocation channel_allocations[] = { +/* channel number: 8 7 6 5 4 3 2 1 */
Do we need to set ca_index explicitly? Any case ca_index != array index?
+static void init_channel_allocations(void) +{
- int i, j;
- struct cea_channel_speaker_allocation *p;
- for (i = 0; i < ARRAY_SIZE(channel_allocations); i++) {
p = channel_allocations + i;
You should zero-initialize p->channels and p->spk_mask here...
for (j = 0; j < ARRAY_SIZE(p->speakers); j++)if (p->speakers[j]) {p->channels++;p->spk_mask |= p->speakers[j];}- }
... because patch_intel_hdmi() may be called multiple times (either multiple codecs or reconfiguration via hwdep) as below.
@@ -455,6 +642,8 @@ static int patch_intel_hdmi(struct hda_c
snd_hda_eld_proc_new(codec, &spec->sink);
- init_channel_allocations();
- return 0;
}
thanks,
Takashi