[alsa-devel] [RFC PATCH] ASoC: pcm512x: Implement the set_bclk_ratio interface

[Dimitris Papavasiliou]

On Tue, Jan 15, 2019 at 10:06 AM Peter Rosin <peda at axentia.se> wrote:
> ...and when double-checking that, this dai op is only ever called from
> snd_soc_dai_set_bclk_ratio, and that function is in turn not called from
> anywhere AFAICT. What's the point of this dai op anyway? Or, what am I
> missing?

Well, my use for this, would be to allow the machine driver to call
snd_soc_dai_set_bclk_ratio, in order to explicitly set the frame
width.  This would allow it to use 32-bit frames for 24-bit data and
avoid the fractional dividers that would otherwise result.  Right now,
the machine driver (which lives in the Raspberry Pi kernel tree) uses
a workaround for this, that relies on a patch made to the CODEC driver
to half-support TDM slots, which hasn't be pushed upstream, and
wouldn't be accepted if it had, since it's essentially a hack.  You
can find more details here:

http://mailman.alsa-project.org/pipermail/alsa-devel/2018-December/143507.html

What the intended use for the snd_soc_dai_set_bclk_ratio is, I'm not
so clear about, hence this RFC.