05.04.2015, 20:26, Russell King - ARM Linux kirjoitti: > On Sun, Apr 05, 2015 at 06:46:13PM +0200, Takashi Iwai wrote: >> >> One another question: don't we need to deal with the sample bits in >> sad[2]? > > It should, but I'm very wary about doing that without seeing more > examples of real SADs. Right now, all my examples only support > one SAD with either 2 channel or 6 channel audio at the standard > (basic) 32, 44.1 and 48kHz rates. > > The HDMI / CEA specs are very loose in their wording about the > short audio descriptors. I've no idea whether a sink can provide > (for example) descriptors such as: > > LPCM, 6 channel 32, 44.1, 48kHz > LPCM, 2 channel, 32, 44.1, 48, 96, 192kHz > > or whether have to describe that as a single descriptor. I only > have two TVs to test with here.
For the record, yes, multiple LPCM SADs are relatively common, and I think I've seen some that offered more rates on a stereo SAD than on a multichannel SAD (like in your example). > What I'm concerned about is that when the ALSA parameter refining > starts, we start with (eg) 2-8 channels, 32-192kHz. Given that, > if we invoke the channel restriction before the rate restriction, > we would end up limiting to 2 channel at 32-192kHz. If we apply > the restrictions in the opposite order, we'd restrict to 6 > channel, 32-48kHz. Neither are obviously correct in this > circumstance, and I don't really see a way to solve it given my > understanding of the way ALSA's parameter refinement works. > > I suspect this is why most HDMI drivers are implemented such that > they take the maximum capabilities over all SADs, which would end > up restricting audio in the above case to: up to 6 channels, at > 32, 44.1, 48, 96 and 192kHz, even though 6 channel @ 192kHz isn't > hasn't been indicated as supported. > > Most of this is speculation though, based off what is in the > documentation. As I say, I don't have enough real-world examples > to get a feel for what manufacturers _actually_ do to give a hint > as to how the documentation should be interpreted. > > So, maybe I should just copy what everyone else does and take the > maximum of all descriptors... > -- Anssi Hannula
