[alsa-devel] [RFC PATCH 1/2] ASoC: simple-card: add support for bclk_ratio

[Russell King - ARM Linux admin]

On Tue, Feb 26, 2019 at 11:31:15AM -0500, Sven Van Asbroeck wrote:
> On Tue, Feb 26, 2019 at 10:45 AM Russell King - ARM Linux admin
> <linux at armlinux.org.uk> wrote:
> >
> >
> > I can't see how you'd extend a single I2S setup to support multi-
> > channel audio without either adding more I2S data lines or adding
> > additional WS signals (so making it e.g., a binary number).
> >
> 
> That's a very good point too. In light of this, I struggle to understand how
> the ssl_ssi can specify this:
> 
> static struct snd_soc_dai_driver fsl_ssi_dai_template = {
>         .playback = {
>                 .stream_name = "CPU-Playback",
>                 .channels_min = 1,
>                 .channels_max = 32,
>         },
> 
> There is talk in the manual about "network mode", which could work by changing
> the LRCLK only at the first slot - thereby allowing clients to receive all
> slots just by counting, as long as they know the slot size?
> 
> LRCLK   _____/-----------------\_____/---------
> DATA    SLOT1|SLOT2|SLOT3|SLOT4|SLOT1

>From what I gather, these are described using SND_SOC_DAIFMT_DSP_A
and SND_SOC_DAIFMT_DSP_B dai formats, and the parameters are
controlled not through snd_soc_dai_set_bclk_ratio() but via
snd_soc_dai_set_tdm_slot().

So, IMHO, the TDM formats should be disregarded from consideration
here.  Mark, ack?

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