Re: [alsa-devel] [PATCH linux-next v2 9/9] ASoC: rsnd: add busif property to dai stream

From: Kuninori Morimoto
Date: Mon Oct 08 2018 - 20:44:19 EST

Hi Jiada

> SSI can work in following modes
> 1. Basic Mode: (channel 1, 2, 4, 6, 8, 16)
> 2. TDM Extended Mode: (channel 6, 8)
> 3. TDM Split Mode: (channel 1, 2)
> 4. TDM Ex-Split mode: (Channel 2, 4, 6, 8, 10)
> > So, my opinions for BUSIFn support are
> > - SSI mode should be selected automatically
> can you give me your idea, how to automatically determine working mode,
> when user plays 2 channel stream on playback dai-link

If my understanding was correct, we can do like this
If DT indicated sound card has dai-link x N, tdm-slots = <M>,
If (N, M) = (1, 2) : Basic mode
If (N, M) = (1, >2): TDM mode
If (N, M) = (2, 4) : TDM Split mode
If (N, M) = (2, >4): TDM Ex-Split mode
If (N, M) = (>2, 8): TDM Split mode

Maybe some combination was wrong, but we can do something like this ?

> for example user asks dai-link0 to playback 2ch audio stream,
> driver can't determine which mode to work, as it can be Basic mode,
> Split mode or Ex-Split mode.

Why do we need to use Basic mode if HW has TDM Split mode connection?
If user playbacks 2ch audio in such situation,
we can use TDM Split mode (= only 2ch has sound, other channel has no sound ?)
user might start to playback for other channels.
I'm not sure how it works...

> > - BUSIFn connection should be selected on DT
> since which BUSIFx is used during audio data transfer, is not
> consideration of user,
> I think your previous suggestion, (automatically select BUSIFx) makes
> more sense

I'm not yet sure detail, but in your idea, does it mean,
BUSIFx connection might be exchanged runtime ?
I think BUSIFx connection shouldn't exchanged runtime IMO.
Otherwise, sound position can't be fixed, and user can't control
sound, I think...

Best regards
Kuninori Morimoto