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:

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On Mon, Jan 04, 2021 at 09:24:49PM +0000, Mark Brown wrote:  

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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.  

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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.

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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.

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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.  

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Components we're calling things like "extcon"...  

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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.


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