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:
> 1) its number of allocated channels = substream->runtime->channels
> 2) 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
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