ASoC: SOF: ipc4-topology: set playback channel mask

[bardliao]

Currently, we send all channels to all amps and copy the channel_mask to all ALH DMAs in playback. However, the amp may not have the capability to run any process and SOF may need to split the channels and send specific data channel to each amp. In that case, we need to split the channel_mask in ALH DMA.
Copy the channel mask only if the widget channel count is the same the FE channels for playback, otherwise, split the channels among the aggregated DAIs. Like what we did in capture.

[Copilot]

Pull Request Overview

This PR fixes channel mask handling in SOF (Sound Open Firmware) IPC4 topology for playback scenarios. It addresses cases where amplifiers cannot process all channels and SOF needs to split channels among DAIs.

• Updates playback channel mask logic to conditionally use full channel mask or split channels
• Removes hardcoded playbook channel mask assignment in favor of calculated masks
• Aligns playback behavior with existing capture channel splitting logic

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[Copilot]

The condition checks for snd_soc_dapm_dai_in (playbook) but sets step = 0 which effectively disables the shifting logic in the channel mask calculation below. This magic number should be documented or made more explicit with a named constant or explanatory comment about why step is zeroed for this condition.

Suggested change

	if (swidget->id == snd_soc_dapm_dai_in && ch_count == out_ref_channels) {
	mask = ch_mask;
	mask = ch_mask;
	/*
	* For DAI input widgets where all channels are used,
	* disable the shifting logic in the channel mask calculation
	* by setting step to 0. This ensures the same mask is applied
	* to all devices.
	*/

[Copilot]

There's a grammatical error in the comment. 'in the case' should be 'in this case' for proper English grammar.

Suggested change

	* Set the same channel mask if the widget channel count is the same
	* as the FE channels for playback as the audio data is duplicated
	* for all speakers in the case. Otherwise, split the channels
	* for all speakers in this case. Otherwise, split the channels

[ujfalusi]

I would rather:

if (swidget->id == snd_soc_dapm_dai_in && ch_count == out_ref_channels) {
	/* Set the same mask to all devices if ch_count == out_ref_channels */
	step = 0;
	mask = ch_mask;
} else {
	step = ch_count / blob->alh_cfg.device_count;
	mask =  GENMASK(step - 1, 0);
}

[ujfalusi]

but the comment is somehow strange...
"Set the same mask to all devices" and swidget->id == snd_soc_dapm_dai_in, so it is not all devices, but DAIs..

[bardliao]

but the comment is somehow strange... "Set the same mask to all devices" and swidget->id == snd_soc_dapm_dai_in, so it is not all devices, but DAIs..

I mean blob->alh_cfg.mapping[i].channel_mask, commit message updated.

[bardliao]

@ujfalusi @ranj063 @lgirdwood This PR is for 4 channel playback. However, the request was postponed. Do we want to merge it now or wait until we really need it?

[lgirdwood]

@singalsu good for your use cases ?