Re: [RFC 0/4] ASoC: Add HDA HDMI codec driver

[Russell King - ARM Linux <linux@arm.linux.org.uk>]

On Fri, Oct 09, 2015 at 04:17:48PM +0100, Vinod Koul wrote:
> On Fri, Oct 09, 2015 at 01:52:07PM +0100, Russell King - ARM Linux wrote:
> > On Fri, Oct 09, 2015 at 01:28:45PM +0100, Vinod Koul wrote:
> > > Yes, this patch series attempts to add yet another HDMI driver to
> > > ASoC. This codec appears as HDA codec over HDA link. Although
> > > the codec reside in display we have a HDA link from audio block
> > > to this codec. The communication to codec is over HDA link
> > > 
> > > Thanks to i915 component infrastructure, we do not need to worry
> > > about keeping the codec on, this is done by i915 for us.
> > > 
> > > Based on discussion with Mark here at ELCE and other attempts by
> > > various folks on HDMI, I wanted to show on list the stuff we have
> > > done and discuss and try to see how we converge various attempts
> > > 
> > > The driver here only supports stereo and doesn't do multichannel
> > > just yet, will add later once we converge here. The support for
> > > using i915 component notification by David will be added later
> > > on.
> > 
> > I notice that you don't limit the capabilities of the ASoC device to
> > the capabilities of the HDMI sink - is that an intentional design
> > decision, or is it handled some other way?
> > 
> > I think that's the "interesting" part of HDMI - how should audio find
> > out the capabilities on the HDMI sink, and that's the area which people
> > have been struggling to design and come to some sort of concensus over.
> 
> I think we should set capabilities based on the sink capabilities. And these
> should be set after reading the ELD. We want to do that when stream is
> opened and we query ELD and set the constarinats based on ELD.
> I have not added that code but this was the idea and was planned to come
> after this

Note that there's sound/core/pcm_drm_eld.c which should help you with
that.  Please help to improve it if it doesn't meet your needs - it's
a helper precisely to set the constraints based on ELD.

It tries to find the best fit of sample rate vs channels given a ELD
array of SADs.

> So we have discussed this with Takashi and the general idea is that we add a
> SW mechanism as well which will be based on i915 component framework to read
> ELD reliably from display driver
> 
> I think as a general idea all the hdmi audio drivers should rely on component
> interface generically to read ELD/ get notification (that was added
> recently). Today on audio we have i915 component interface and IMHO this
> should be made a generic audio-display component interface and used by all.
> The callbacks are not really HDA based. But I don't really know on other
> arch if that is doable or not...

Do you have a pointer to this work?

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