Re: [PATCH v6 2/8] regulator: dt-bindings: Document max8997-pmic nodes

Timon Baetz
2021-01-08T15:17:41Z

On Wed, 6 Jan 2021 14:59:31 +0000, Mark Brown wrote:
> On Tue, Jan 05, 2021 at 05:55:29PM +0100, Krzysztof Kozlowski wrote:
> > On Mon, Jan 04, 2021 at 09:24:49PM +0000, Mark Brown wrote:
>
> > > I'm not sure I follow, sorry? Either the core driver can parse the
> > > bindings enough to know what children it has or (probably better) it can
> > > instantiate the children unconditionally and then the function drivers
> > > can figure out if they need to do anything.
>
> > Currently the MFD parent/core driver will instantiate children
> > unconditionally. It would have to be adapted. With proposed bindings -
> > nothing to change. MFD core already does the thing.
>
> We're not talking massive amounts of code here, but we are talking ABI
> for a DT update.
>
> > The point is that function drivers should not be even bound, should not
> > start to probe. Otherwise if they probe and fail, they will pollute the
> > dmesg/probe log with failure. With the failure coming from looking for
> > missing of_node or any other condition from parent/core driver.
>
> There will only be an error message if one is printed, if we can do a
> definitive -ENODEV there should be no need to print an error.
>
> > > > Another point, is that this reflects the real hardware. The same as we
> > > > model entire SoC as multiple children of soc node (with their own
> > > > properties), here we represent smaller chip which also has
> > > > sub-components.
>
> > > Components we're calling things like "extcon"...
>
> > I am rather thinking about charger, but yes, extcon as well. Either you
> > have USB socket (and want to use associated logic) or not.
>
> Right, I'm just saying we don't need to add new device nodes reflecting
> implementation details into the DT to do that.

I'm not sure I can contribute that much to this discussion (this is my
first proper kernel patch, also I don't really understand the argument).
FWIW I looked at other MFD devices while implementing this like max77836,
max77693, max77650, max77843 (just to name a few).
Assigning of_node to sub-devices using sub-nodes with compatible strings
seemed to be a common pattern for MFD devices.
Muic needs a node to be used with extcon_get_edev_by_phandle().
Charger needs a node to reference a regulator.