At Tue, 31 Aug 2010 08:41:53 -0700, Stephen Warren wrote: > > Takashi Iwai wrote: > > > > At Mon, 30 Aug 2010 10:11:09 -0700, > > Stephen Warren wrote: > > > > > > It looks like even though some NVIDIA MCPs have min/max channel of 2/8, not > > > all HW supports the intermediate # channels (4 and 6) over HDMI. Various > > > combinations are supported on various HW: 2, 2/8, 2/6/8, 2/4/6/8. > > > > > > At present, when an application uses an unsupported number of channels, > > > playback appears to operate correctly, but the HW doesn't actually send the > > > audio data over HDMI. > > > > > > Is it possible for patch_nvhdmi.c to simply program codec the HW in 8-channel > > > mode even though the controller is only sending 4-/6-channel data? > > > > I'm not sure whether HD-audio codec can have a /dev/zero-kind of stream. > > It's possible to set up but I don't think it's worth. > > It'd be far easier to omit 4 and 6-channels for such a case. > > > > > I'm not > > > sure if this would cause the codec to get out of sync with the controller's > > > data stream. Would the controller end up grabbing 8 channels worth of data > > > from the stream at a time, have no way to synchronize to the start of each > > > sample, and hence end up packing e.g. 2 complete 4 channel samples into a > > > single 8 channel sample? > > > > > > If not, it seems that patch_nvhdmi.c should be modified so that each codec's > > > _open() function returns an error for unsupported rates. I can code that up > > > if we need. > > > > Do you mean for unsupported channels? > > Oops, yes. > > Do you think that's the correct fix? > > If the driver errors out the open, will a plug: (or other non hw:) ALSA device > dynamically "upsample" a 4-channel stream to the next supported (8-channel), or > will the user application have to handle this? alsa-lib can do make working (e.g. via upmix plugin). But other audio backend can do it by itself. IMO, telling the truth is a better approach. It is 4-channel, after all. > > > Unfortunately, it doesn't look like it's possible for applications to query > > > this information from ALSA, since a hw_params_t exposes just a min/max > > > channel count rather than a mask. > > > > It can be also masked. > > Are you saying the APIs already support a mask for channel count, and I just > didn't find it, or that the APIUs should be updated to report a mask? You can pass the list as hw_constraint. Look for drivers using struct snd_pcm_hw_constraint_list. thanks, Takashi _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
