ASoC: SOF: Add Virtual DAI support for i.MX8M

[SurajSonawane2415]

This PR is part of the GSoC 2025 Project: Add Virtual DAI Component to SOF and is based on SOF Issue #9349.

We introduce a new SOF_DAI_VIRTUAL type and its associated support to enable audio pipelines that do not rely on physical DAI hardware. This is useful in the following scenarios:

• Debugging and rapid prototyping: Quickly create and test audio pipelines without needing actual hardware.
• Software loopback preparation: Lays the groundwork for a memory-to-memory audio pipeline within SOF.

Motivation

• Debugging & prototyping: Create/test pipelines without hardware.
• Loopback preparation: Foundation for memory-to-memory audio pipelines.

Key Changes

• Add SOF_DAI_VIRTUAL type and config struct.
• Define topology tokens for Virtual DAI.
• Extend IPC3 topology parsing for Virtual DAI.
• Add Virtual DAI entry in i.MX8M SOF backend.
• Update sof_ipc3_pcm_dai_link_fixup to handle Virtual DAI.

Tested above changes on IMX8MP EVK board

Logs:

[   10.300681] sof-audio-of-imx8m 3b6e8000.dsp: Topology: ABI 3:29:1 Kernel ABI 3:23:1
[   10.300750] sof-audio-of-imx8m 3b6e8000.dsp: DAI connect: widget name=DAI_VIRTUAL7.OUT, sname=NoCodec-0, id=27
[   10.300758] sof-audio-of-imx8m 3b6e8000.dsp: DAI connect: expect id dai_in=27 or dai_out=28
[   10.300763] sof-audio-of-imx8m 3b6e8000.dsp: DAI connect: checking stream_name='NoCodec-0' for link='NoCodec-0'
[   10.300768] sof-audio-of-imx8m 3b6e8000.dsp: DAI connect: MATCH found for NoCodec-0
[   10.300773] sof-audio-of-imx8m 3b6e8000.dsp: DAI connect: widget DAI_VIRTUAL7.OUT set on CPU DAI virtual_dai (stream 0)
[   10.300778] sof-audio-of-imx8m 3b6e8000.dsp: tplg: connected widget DAI_VIRTUAL7.OUT -> DAI link NoCodec-0
[   10.300980] sof-nocodec sof-nocodec: ASoC: Parent card not yet available, widget card binding deferred
[   10.300996] sof-audio-of-imx8m 3b6e8000.dsp: tplg: config VIRTUAL_DAI7 fmt 0x1

Related Work

• Zephyr PR: #95233 drivers: dai: Add virtual DAI driver and tests
  Includes Virtual DAI driver, DTS binding, Kconfig/CMake updates, and ztest-based API tests.

• SOF PR: #10147 dai: Add support for Virtual DAI for rapid prototyping and software loopback
  Adds Virtual DAI support on i.MX8MP with topology and emul_dma integration for software-based audio pipelines.

• linux-imx nocodec feature commit: Enabled NoCodec support for the i.MX8M platform to allow pipeline testing without real codecs.
  Link: nocodec-commit

Current Status

• Verified on i.MX8MP EVK with NoCodec: probe/config/removal working.
• Playback/capture validation ongoing.
• emul_dma integrated, but data copy still incomplete.

Future Work

Implement proper playback (log/discard) and capture (zero-filled).