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

[Mark Brown]

On Tue, Feb 26, 2019 at 05:03:49PM +0000, Russell King - ARM Linux admin wrote:
> On Tue, Feb 26, 2019 at 11:31:15AM -0500, Sven Van Asbroeck wrote:

> > 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

Roughly, yes - the DSP formats are formats which only care about one
edge of the LRCLK, the difference being if the first data bit is the
same clock cycle as the transition or the next clock cycle.

> 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?

I'd expect set_bclk_ratio() to cover all formats - usually the hardware
either has zero flexibility when it comes to the LRCLK format or isn't
super bothered, this stuff is mainly used to adapt the more flexible
hardware to the less flexible hardware.

TDM is definitely something that only really makes sense with DSP
formats though, I2S TDM is just weird.
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