On 12.01.2011 18:42, Stephen Warren wrote:
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:
- 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?
Usage of those formats is indeed somewhat limited.
This is true especially with ALSA, since if you open a device with 3 channels, it generally means left+right+rearleft instead of the likely intended left+right+lfe or left+right+center.
And yes, (1) is enough, the below (2) was meant to be an additional future development.
- 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?
No, alsa-lib would insert a dummy channel, so it gets through the hw_constraint as it is now a 4 channel stream. This is what already happens when the constrains are added (and the alsa device is used via 'plug', e.g. "plug:'hdmi:CARD=NVidia,DEV=3'").
What (2) would mean is that alsa-lib also informs the kernel of the actual layout (including 4th channel being a dummy one) so that patch_hdmi can set the infoframe correctly.
(and in case of 7x hardware, libalsa would notice that the kernel driver has a channel map different from alsa and do some channel remapping).