[alsa-devel] [PATCH] ALSA: hda: Disable 4/6 channels on some NVIDIA GPUs.

Stephen Warren swarren at nvidia.com
Wed Jan 12 17:42:22 CET 2011

Anssi Hannula wrote:
> On 11.01.2011 19:41, Stephen Warren wrote:
> > Anssi Hannula wrote:
> >> On 10.01.2011 18:19, Nitin Daga wrote:
> >>> Added hardware constraint in patch_hdmi.c to disable
> >>> channels 4/6 which are not supported by some older
> >>> NVIDIA GPUs.
> >>
> >> And 3/5/7, which do not seem to work either with my 0x0007.
> >
> > Are 3/5/7 channels supported by any vendor?
> Actually, I just tested and just transmitting 3-channel data with extra
> 4th dummy channel while setting the Audio InfoFrame fields to indicate a
> 3 channel stream makes it work.
> So it would seem (to me) like the best approach would be:
> 1. Add a hw_constraint to prevent odd channel counts (easy)

That seems enough to me. I'm not sure that 3/5/7 channels are a format
that there is much use-case for?

> 2. Provide some way for alsa plug (and the user application) to indicate
>    the "actual/original" channel count/layout without dummy channels,
>    so that the infoframe can be set correctly.
>    This is harder, and I guess should probably be implemented so that
>    the channel remapping issue on older nvidia hw will be fixed as well.

Hmm. That sounds kinda complex. If constraints prevent the application
from using e.g. 3-channel, then implementing (2) means the plugin would
have to also modify the constraints to re-allow 3-channel, so the
application could actually use it, no?


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