On Thu, Dec 26, 2024 at 04:30:17PM +0800, Chen-Yu Tsai wrote:
> Hi,
>
> On Wed, Dec 4, 2024 at 3:22 AM Nícolas F. R. A. Prado
> <nfraprado@xxxxxxxxxxxxx> wrote:
> >
> > Remove hardcoded dmic codec from the UL_SRC dai link to avoid requiring
> > a dmic codec to be present for the driver to probe, as not every
> > MT8188-based platform might need a dmic codec. The codec can be assigned
> > to the dai link through the dai-link property in Devicetree on the
> > platforms where it is needed.
>
> A followup question about this. The DMICs on the Chromebooks are attached
> to the PMIC codec's input side, which then converts the signals to standard
> I2S and passes them out to the SoC through its AIF1. So the original code
> was somewhat incorrect, though it works.
>
> How should we describe such a connection, given that the MediaTek sound
> bindings aren't a full graph?
What you're describing is that the hardware topology looks like this:
-------------------- --------------------
| SoC | | MT6359 PMIC |
| UL_SRC BE | <--- | AIF1 AIN0_DMIC | <-- DMic
-------------------- --------------------
But that the dailink definition in the machine driver had the DMic codec
connected directly to the UL_SRC BE instead, alongside the connection to the
PMIC, unlike the topology above.
My understanding is that the dmic codec was added simply to allow the usage of
the wakeup-delays. From [1] it appears that DAI connections between two codecs
are possible, though rare. So the PMIC -> DMic connection description might be
possible in that way, although I'm not sure it brings any benefits besides
closer resembling the hardware topology.
[1] https://www.kernel.org/doc/html/latest/sound/soc/codec-to-codec.html
>
> > No Devicetree currently relies on it so it is safe to remove without
> > worrying about backward compatibility.
>
> Removing it didn't seem to cause any issues for the Chromebooks that
> do actually have DMICs. I suspect the only difference would be that
> the wakeup-delays no longer apply correctly.
That's my guess too.
Thanks,
Nícolas
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