On Thu, 2 Jan 2014 13:10:45 +0000 Mark Brown broonie@kernel.org wrote:
On Thu, Jan 02, 2014 at 01:44:37PM +0100, Jean-Francois Moine wrote:
I still don't understand. There is already such cases in the Cubox: the S/PDIF output from the kirkwood audio controller is connected to both the HDMI transmitter and the S/PDIF TOSLINK. So, in the audio controller, the port @1 defines the S/PDIF DAI and the endpoints @0 and @1 point to the remote DAIs, creating 2 snd DAI links:
port@1 { audio_hdmi_spdif: endpoint@0 { remote-endpoint = <&hdmi_spdif_audio>; }; audio_spdif: endpoint@1 { remote-endpoint = <&spdif_audio>; }; };
Oh, so the endpoints are virtual and that's supposed to be three things wired together rather than a single device with multiple links? That's really not very clear from reading the above and seems cumbersome - every device will want to explicitly identify every other device on the link and any configuration is going to either need to be replicated on every device or we'll need to check lots of places for the configuation. It seems like this will be hard to work with.
No, the 'endpoint' <=> 'remote-endpoint' is a point to point relation. Even if the sources and sinks are not explicitly defined, the way the stream flows is easy to find: the main source is always in the 'audio-controller' node
sound { compatible = "media-audio"; audio-controller = <&audio1>; };
and, then, the controller ports are sources (CPU DAIs) and the associated remote ports are sinks (CODEC DAIs).
With many levels, once the remote (sink) ports are identified, in the devices where such sinks exist, the remaining ports are sources.
Usually, the devices don't have to know to which other device they are connected, and, yes, the reverse pointer sink to source is not useful.
But the way (link) the audio stream comes from may be important to know. This is the case for the HDMI CODEC which must tell the HDMI transmitter from which hardware port(s) ('reg') it may get the audio stream. That's why, the HDMI encoder has two endpoints in its audio port, each endpoint being a different CODEC DAI.