Re: [SPAM]Re: [PATCH v3 4/5] dt-bindings: clock: mediatek: update audsys documentation to adapt MFD device

[Ryder Lee <ryder.lee@mediatek.com>]

On Wed, 2018-02-28 at 09:13 -0600, Rob Herring wrote:
> >> There are several problems you need to fix. First,
> >> "mediatek,mt2701-audsys" is not documented. It is only used in the
> >> example. Second, bindings/arm/mediatek/mediatek,audsys.txt should move
> >> to bindings/sound/ if it is only audio related functions. Or perhaps
> >> just combine the 2 documents because it is all inconsistent currently.
> >
> > Because the series crossed subsystems but didn't apply at the same time.
> >
> >> The 2 documents are inconsistent as to what is the relationship of
> >> -audsys and -audio (afe) nodes. mt2701-afe-pcm.txt shows that the AFE
> >> is already a child of -audsys. The -audsys node should have
> >> #clock-cells. It should also not be a simple-mfd (another
> >> inconsistency in the binding) because it needs to probe first to
> >> provide clocks to child nodes, and then trigger probing the child
> >> nodes.
> >
> > This is the 1st version I sent before, and the clock parts still under
> > review :( .  But yes, the 2 inconsistent documents should be fixed -
> > this may depend on what we end up doing with the DT appearance.
> >
> > IMHO, apart from overlapping regions with other functions I didn't see
> > any difference between audsys and other clock drivers (providers).
> >
> > For the sake of uniformity, I make the 2 sub-devices parallel and move
> > "simple-mfd" to the top, and the sequences should actually be handled
> > through "probe deferral mechanism" - that would make this kind of
> > situations much easier to manage.
> 
> If a child node has a dependency on the parent, probe deferral is not
> the correct solution. The parent should probe first and control
> probing of the chlidren. "simple-mfd" is intended for cases where
> there is no dependency on the parent node.

In my opinion, they are just the provider-consumer relationship not the
parent-child relationship, and we leverage this mechanism for most CCF
users.  Please correct me if I'm wrong.  

That's why I sent the a new one to separate them (but I forgot to modify
mt2701-afe-pcm.txt).

> > BTW, I could make the AFE driver be instantiated/probed from the clock
> > driver but this seems superfluous to me.  Just make sure is this what
> > you want?
> 
> I would think it would be the other way around. The AFE driver creates
> some clocks. Whether that's a separate driver or a single driver is a
> kernel issue that has nothing to do with the binding. IIRC, there's
> several examples in display controllers and camera interfaces where
> those drivers are also clock providers.

I've look at some display drivers, but couldn't find a good case. The
different is, that the driver I saw provides clocks to other submodules,
while the AFE is just a user. So it's odd if we register AFE itself as a
clock provider (and use the clocks it generates).