Message-ID: <z2wrzts6cgunxs5tc764izvrfi4i2d637zpt6tj5f4piry6j66@cke2yxhih6dg>
Date: Tue, 24 Jun 2025 00:08:03 +0200
From: Sebastian Reichel <sebastian.reichel@...labora.com>
To: Amit Sunil Dhamne <amitsd@...gle.com>
Cc: Rob Herring <robh@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Badhri Jagan Sridharan <badhri@...gle.com>, 
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>, "Rafael J. Wysocki" <rafael@...nel.org>, 
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@...nel.org>, Kyle Tso <kyletso@...gle.com>, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org, 
	linux-pm@...r.kernel.org
Subject: Re: [PATCH v2 1/5] dt-bindings: connector: extend ports property to
 model power connections

Hi,

On Tue, May 20, 2025 at 01:10:25PM -0700, Amit Sunil Dhamne wrote:
> Hi Rob,
> 
> Thanks for your response!
> 
> On 5/14/25 12:42 PM, Rob Herring wrote:
> > On Wed, May 07, 2025 at 06:00:22PM -0700, Amit Sunil Dhamne wrote:
> >> Extend ports property to model power lines going between connector to
> >> charger or battery/batteries. As an example, connector VBUS can supply
> >> power in & out of the battery for a DRP.
> >>
> >> Additionally, add ports property to maxim,max33359 controller example.
> >>
> >> Signed-off-by: Amit Sunil Dhamne <amitsd@...gle.com>
> >> ---
> >>  .../bindings/connector/usb-connector.yaml          | 20 +++++++++++------
> >>  .../devicetree/bindings/usb/maxim,max33359.yaml    | 25 ++++++++++++++++++++++
> >>  2 files changed, 38 insertions(+), 7 deletions(-)
> >>
> >> diff --git a/Documentation/devicetree/bindings/connector/usb-connector.yaml b/Documentation/devicetree/bindings/connector/usb-connector.yaml
> >> index 11e40d225b9f3a0d0aeea7bf764f1c00a719d615..706094f890026d324e6ece8b0c1e831d04d51eb7 100644
> >> --- a/Documentation/devicetree/bindings/connector/usb-connector.yaml
> >> +++ b/Documentation/devicetree/bindings/connector/usb-connector.yaml
> >> @@ -181,16 +181,16 @@ properties:
> >>  
> >>    port:
> >>      $ref: /schemas/graph.yaml#/properties/port
> >> -    description: OF graph bindings modeling a data bus to the connector, e.g.
> >> -      there is a single High Speed (HS) port present in this connector. If there
> >> -      is more than one bus (several port, with 'reg' property), they can be grouped
> >> -      under 'ports'.
> >> +    description: OF graph binding to model a logical connection between a device
> >> +      and connector. This connection may represent a data bus or power line. For
> >> +      e.g. a High Speed (HS) data port present in this connector or VBUS line.
> >> +      If there is more than one connection (several port, with 'reg' property),
> >> +      they can be grouped under 'ports'.
> > 'port' and 'port@0' are equivalent. So you can't be changing its 
> > definition.
> 
> Noted!
> 
> 
> > I'm not sure showing a power connection with the graph is the right 
> > approach.
> 
> I want to provide some more context and rationale behind using this design.
> 
> From a hardware perspective:
> 
> The max77759/max33359 IC has Type-C port controller, charger, fuel gauge
> (FG) ICs. The Vbus from the connector goes to/from the TCPC and connects
> with the charger IP via circuitry & from there on to the battery. The FG
> is connected to the battery in parallel. As it can be seen that while
> these IPs are interconnected, there's no direct connection of the fuel
> gauge & the connector.
> 
> For this feature, I am interested in getting the reference to the FG. As
> per graph description: "...These common bindings do not contain any
> information about the direction or type of the connections, they just
> map their existence." This works for my case because I just want the
> connector to be aware of the Fuel gauge device without imposing a
> specific directionality in terms of power supplier/supplied. This is
> also the reason why I didn't use
> "/schemas/power/supply/power-supply.yaml#power-supplies" binding.
> 
> > We have a binding for that already with the regulator binding.
> 
> I haven't explored the option of using regulator bindings. But in my
> case I am interested in fuel gauge and unfortunately, they're modeled as
> power_supply devices.

From hardware point of view there is no direct connection at all
between the fuel gauge and the connector. The usual hardware
connection is

connector -> charger -> battery

With the charger potentially supporting reverse operation to provide
energy from the battery to the connector (with "battery" I assume
a "smart" battery, so the raw cells and some kind of fuel gauge).

Thus the following example should properly document the hardware
connections:

---------------------------------------
typec-connector {
    /* ... */
};

charger {
    /* ... */
    power-supplies = <&connector>;
};

fuel-gauge {
    /* ... */
    power-supplies = <&charger>;
};
---------------------------------------

It means instead of the direct graph lookup for the fuel gauge,
you would need a function walking through the graph build by the
power-supplies phandles. But it also means that the DT properly
describes the hardware instead of adding random graph connections.

Greetings,

-- Sebastian

> > Perhaps the connector needs to be a supply. It's already using that 
> > binding in the supplying power to the connector case.
> 
> Want to clarify, in this case you mean
> /schemas/regulator/regulator.yaml#*-supply$ right?
> 
> Adding to my response above, the reason I don't want to impose a
> directionality in terms of supplier/supplied is that in case of USB Dual
> Role Port they're dynamic i.e., when USB is source, the power is
> supplied out of the battery (battery/FG will be supplier) and in case
> USB is sink, battery is supplied power. Whether the connector port is in
> source or sink role is determined on a connection to connection basis.
> Also, the knowledge of the supply direction is of no consequence for
> this feature.
> 
> 
> Please let me know what you think.
> 
> Thanks,
> 
> Amit
> 
> 
> > Rob
> 

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