Currently, ASoC supports dailinks with the following mappings:
1 cpu DAI to N codec DAIs
N cpu DAIs to N codec DAIs
But the mapping between N cpu DAIs and M codec DAIs is not supported.
The reason is that we didn't have a mechanism to map cpu and codec DAIs

This patch suggests a new snd_soc_dai_link_codec_ch_map struct in
struct snd_soc_dai_link{} which provides codec DAI to cpu DAI mapping
information used to implement N cpu DAIs to M codec DAIs
support.

When a dailink contains two or more cpu DAIs, we should set channel
number of cpus based on its channel mask. The new struct also provides
channel mask information for each codec and we can construct the cpu
channel mask by combining all codec channel masks which map to the cpu.

The N:M mapping is however restricted to the N <= M case due to physical
restrictions on a time-multiplexed bus such as I2S/TDM, AC97, SoundWire
and HDaudio.
Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Reviewed-by: Péter Ujfalusi <peter.ujfalusi@linux.intel.com>
Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Link: https://lore.kernel.org/r/20230607031242.1032060-2-yung-chuan.liao@linux.intel.comSigned-off-by: Mark Brown <broonie@kernel.org>