[alsa-devel] HDMI audio: TV vs. codec supported sample rates

[Stephen Warren]

Jaroslav Kysela wrote:
> On Tue, 3 Aug 2010, Stephen Warren wrote:
> 
> > A user has the following setup:
> >
> > A GPU which supports audio-over-HDMI. The codec supports sample rates
> > 32000 44100 48000 88200 96000 176400 192000 (from
> > /proc/asound/card1/codec#1). However, the user's TV supports only sample
> > rates 44100 48000 88200 (from /proc/asound/card1/eld*).
> >
> > When the user plays sound with sample rate 22050, they hear nothing.
> > Sound with sample rates supported by the TV works OK.
> >
> > My question: Is the HDA codec driver supposed to dynamically adjust its
> > list of supported sample rates based on the ELD content, or is the ALSA
> > library somehow supposed to detect the subset of rates supported in HW
> > and convert the sample rate in SW before sending the audio to the
> > driver?
> 
> The driver must return the correct list of supported sample rates.
> Otherwise alsa-lib thinks that the invalid sample rate is supported in the
> hardware or driver.

OK, that makes sense. Is this the responsibility of the codec driver (e.g.
patch_nvhdmi.c) or something in the core HDMI code (e.g. patch_hdmi.c, or
hda_*.c)

I don't see anything in patch_intelhdmi.c that relates to sample rate
support at all. However, I see that patch_nvhdmi.c contains e.g.:

static struct hda_pcm_stream nvhdmi_pcm_digital_playback_8ch_89 = {
        .substreams = 1,
        .channels_min = 2,
        .rates = SUPPORTED_RATES,

Should .rates not be initialized here, so that some automatic ELD-parsing
logic gets triggered to fill this in later?

Thanks.

-- 
nvpublic