[alsa-devel] radeon multi-channel lpcm

Pierre Ossman pierre-list at ossman.eu
Thu Sep 6 09:52:51 CEST 2012

On Thu, 06 Sep 2012 09:28:52 +0200
Takashi Iwai <tiwai at suse.de> wrote:

> At Thu, 6 Sep 2012 09:09:00 +0200,
> Pierre Ossman wrote:
> > 
> > But if you're saying that the hardware doesn't really need the ELD,
> > then steps 3-4 could be replaced by a pure software channel.
> No, what I meant is about the audio codec perspective.  From the audio
> codec, it has no direct hardware access to GPU that actually handles
> the ELD register things.  It always communicate via HD-audio verbs to
> send/receive DIP bytes so the actual work is purely in the graphics
> driver side.

I assume "codec" here is in the HDA sense, as in the hardware hiding
somewhere behind the HDA interface.

In the Intel case, I'd say the audio hardware as a whole does have some
back channel to the GPU since a write to a GPU register somehow results
in data in the audio hardware. But yes, it would be a purely graphics
driver thing as it has both the ELD, and access to the registers you
can write to.

I'm working on the assumption that the radeon hardware works in similar
fashion as the Intel ones.

> > This would
> > be convenient as it is currently unknown how to do 3) on radeon.
> > 
> > (2 is currently missing in the radeon driver, but it is trivial to add
> Yeah, that's the big missing piece.

So I'll go poke the AMD people, as I cannot find anything in the public
docs about ELD registers. Hopefully it's not something that's still
classified... :/

     -- Pierre Ossman

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