[alsa-devel] [PATCH v5] ASoC: cs53l30: Add support for Cirrus Logic CS53L30

[Caleb Crome]

On Thu, Jun 2, 2016 at 11:40 AM, Mark Brown <broonie at kernel.org> wrote:
> On Thu, Jun 02, 2016 at 10:40:58AM -0700, Caleb Crome wrote:
>> On Thu, Jun 2, 2016 at 10:17 AM, Mark Brown <broonie at kernel.org> wrote:
>
>> > Well, if you specifically mean TDM as opposed to multi-channel our
>> > general support for that isn't good (mainly due to lack of demand).  It
>> > sounds like you're more interested in multi channel here though.
>
>> I must be missing something.  To me, TDM is synonymous with
>> multi-channel on a single wire. The datasheets of codecs and SoCs
>
> TDM, at least in the sense Linux is using it, is multiple *unrelated*
> audio streams on a single wire.  Any multi-channel audio stream is TDM
> in some sense but the trivial extension to add two or more channels
> isn't really a big deal.  This is for things more complex than just
> stuffing more bytes of data onto a wire where there are going to be some
> timeslots that the device should ignore as they're going to/from other
> devices (or at least other streams even if the same chip is handling
> them).

Hi Mark,
   Thanks for taking the time to describe this to me.  This definitely
comes as a surprise to me.  I assumed that TDM mode simply means
multi-channels on a single wire (which is what it means in all the
datasheets).

Just so I have this straight, TDM in the linux sense is putting say,
6-channels on one wire where the channels are from logically different
places? i.e. chanels 0-1 are from bluetooth, 2-3 from analog in, and
4-5 from somewhere else?

So, going back to Nicolin's original question for this email, the
CS53L30, what are the proper DT settings for these modes:
The device can be configured in what amounts to at least 3 different modes:

1) 4-channel, 5-pin ADC interface:  dual I2S: shared BCLK/WCLK/MCLK,
separate data pins for channels 0/1 and 2/3 (SDOUT0/SDOUT1).
2) 4-channel, 4-pin ADC interface: MBLCK/BCLK/WCLK/SDOUT0 only.  Slots
0/1/2/3 on the SDOUT0 pin (synch master)
3) and finally, a multi-codec configuration, where 4 x CS53L30 are
used:  16-channel, 4-pin ADC (what I call TDM) interface, all on the
same 4 pins.  These are very related data streams -- they are
perfectly synchronized in hardware, so perhaps this isn't TDM in the
linux-sense.

>> Nicolin Wrote:
>> Another question is for its TDM support. This chip outputs 4-channel
>> data on two data output pins (SDOUT1 and SDOUT2) as normal mode; it
>> outputs 4-channel data on one data output pin (SDOUT1) as TDM mode.
>> However, the mode selection for a 4-channel recording should depend
>> on the hardware design: whether the SDOUT2 is connected or not. So
>> I am wondering if there is a common way or existing way to indicate
>> this hardware design. Or just by simply defining a new DT property?

As far as I can see he's not trying to define *unrelated* streams in
TDM mode, but very related streams, which is TDM in the
datasheet-sense.  And there not only needs to be a mechanism of
choosing the dual I2S mode, but also which TDM slots to drop the data
in (which I think already exists, right?)


>> What's the linuxy name for what the datasheets call TDM format with
>> slots > 2?  Do we just call that 'multi-channel', or specifically say,
>> 'channels_max > 2'?  I was always under the assumption that's what TDM
>> meant.
>
> We don't particularly call it anything, it's such a trivial extension.

That's not been my experience :-) Getting 16 channels onto a wire has
been anything but trivial because of the lack of SoC driver support
for it.  Perhaps I'm just using the wrong SoCs.

Thanks again,
 -Caleb