[DNM] Audio: Buffers: Add support for DP-to-DP component binding

[singalsu]

Previously binding two DP (Data Processing) scheduled components was rejected with IPC4_INVALID_REQUEST. This patch adds support for DP-to-DP binding by creating a dual ring buffer configuration where each DP module gets its own ring buffer on either side of the intermediate comp_buffer.

Data flow for DP-to-DP:
src_DP -> ring_buf_src -> comp_buffer -> ring_buf_sink -> sink_DP

Changes in helper.c:

• Remove the DP-to-DP bind rejection in ipc_comp_connect().
• Add src_is_dp, sink_is_dp, and dp_to_dp flags to detect the DP-to-DP case.
• Create a second ring_buffer allocated from the source module's heap for the source side of the comp_buffer.
• Track ring_buffer client_count on the DP heap with a NULL guard to avoid unsafe container_of when CONFIG_USERSPACE is disabled.

Changes in audio_buffer.c:

• Change audio_buffer_attach_secondary_buffer() from a global rejection to per-side checks, allowing both secondary_buffer_sink and secondary_buffer_source to be set simultaneously.
• Add a dual-secondary sync path in audio_buffer_sync_secondary_buffer()
  that cascades data through: input ring_buffer -> comp_buffer ->
  output ring_buffer, with rate-limiting applied on the output side.

Changes in ring_buffer.c:

• Add DP heap client_count decrement in ring_buffer_free() with a NULL heap guard, matching the pattern used in comp_buffer_free().

[lgirdwood]

@singalsu so this is not breaking anything atm, but its probably worth while to modify the nocodec topology to have this DP-DP config and see what happens...

[softwarecki]

No, no, no! No comp_buffer between dp modules! Just single ring buffer. We plan to remove comp_buffer and add support for dp-dp connection.

[singalsu]

No, no, no! No comp_buffer between dp modules! Just single ring buffer. We plan to remove comp_buffer and add support for dp-dp connection.

Would be great if that can be done! I need this to have decoder and phase_vocoder in same pipeline without LL components in between throttling the playback data. The phase vocoder consumes at input the audio data at 0.5x to 2.0x speed vs. normal. There can't be LL components with speed higher than 1.0.