linux-kernel - Re: [RFC 1/2] dt-bindings: connector: Add property to set pd timer values

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Message-ID: <20240916163328.GA394032-robh@kernel.org>
Date: Mon, 16 Sep 2024 11:33:28 -0500
From: Rob Herring <robh@...nel.org>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc: Amit Sunil Dhamne <amitsd@...gle.com>,
	krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
	heikki.krogerus@...ux.intel.com, gregkh@...uxfoundation.org,
	linux-kernel@...r.kernel.org, kyletso@...gle.com,
	rdbabiera@...gle.com, Badhri Jagan Sridharan <badhri@...gle.com>,
	linux-usb@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [RFC 1/2] dt-bindings: connector: Add property to set pd timer
 values

On Fri, Sep 13, 2024 at 07:34:27AM +0300, Dmitry Baryshkov wrote:
> On Thu, Sep 12, 2024 at 04:26:25PM GMT, Amit Sunil Dhamne wrote:
> > Hi Dmitry,
> > 
> > On 9/12/24 3:05 AM, Dmitry Baryshkov wrote:
> > > On Tue, Sep 10, 2024 at 05:07:05PM GMT, Amit Sunil Dhamne wrote:
> > > > This commit adds a new property "pd-timers" to enable setting of
> > > > platform/board specific pd timer values for timers that have a range of
> > > > acceptable values.
> > > > 
> > > > Cc: Badhri Jagan Sridharan <badhri@...gle.com>
> > > > Cc: linux-usb@...r.kernel.org
> > > > Cc: devicetree@...r.kernel.org
> > > > Signed-off-by: Amit Sunil Dhamne <amitsd@...gle.com>
> > > > ---
> > > >   .../bindings/connector/usb-connector.yaml     | 23 +++++++++++++++++++
> > > >   include/dt-bindings/usb/pd.h                  |  8 +++++++
> > > >   2 files changed, 31 insertions(+)
> > > > 
> > > > diff --git a/Documentation/devicetree/bindings/connector/usb-connector.yaml b/Documentation/devicetree/bindings/connector/usb-connector.yaml
> > > > index fb216ce68bb3..9be4ed12f13c 100644
> > > > --- a/Documentation/devicetree/bindings/connector/usb-connector.yaml
> > > > +++ b/Documentation/devicetree/bindings/connector/usb-connector.yaml
> > > > @@ -253,6 +253,16 @@ properties:
> > > >       additionalProperties: false
> > > > +  pd-timers:
> > > > +    description: An array of u32 integers, where an even index (i) is the timer (referenced in
> > > > +      dt-bindings/usb/pd.h) and the odd index (i+1) is the timer value in ms (refer
> > > > +      "Table 6-68 Time Values" of "USB Power Delivery Specification Revision 3.0, Version 1.2 " for
> > > > +      the appropriate value). For certain timers the PD spec defines a range rather than a fixed
> > > > +      value. The timers may need to be tuned based on the platform. This dt property allows the user
> > > > +      to assign specific values based on the platform. If these values are not explicitly defined,
> > > > +      TCPM will use a valid default value for such timers.
> > > > +    $ref: /schemas/types.yaml#/definitions/uint32-array
> > > Is it really necessary to use the array property? I think it's easier
> > > and more logical to define corresponding individual properties, one per
> > > the timer.
> > 
> > Thanks for the review. The reason I did it this way was for
> > convenience. If in the future someone else wants add a new timer,
> > it'd be convenient to just add it as a new macro definition in pd.h
> > rather than having to define a new property each time, especially
> > if folks want to add more timers (scales better).
> > There are 3 timers already and I am working to add a fourth in a
> > follow up patch if the current RFC gets accepted.
> > 
> > Please let me know what do you think?
> 
> I'd leave the decision to DT maintainers, but in my opinion multiple
> properties scale better. Having a single value per property is easier to
> handle rather than changing the tagged array.

I agree. And it avoids what looks like a made up number space with the 
defines.

And note that an array of tuples is a matrix in DT defined types, not 
an array.

Rob