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

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Message-ID: <ascu5yztalk62fernydttkywnqemnmjlcflzdyfmt7dzuzngho@vvxrnvwhfdmk>
Date: Fri, 13 Sep 2024 07:34:27 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Amit Sunil Dhamne <amitsd@...gle.com>
Cc: robh+dt@...nel.org, 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 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.

> 
> Regards,
> 
> Amit
> 
> > > +
> > >   dependencies:
> > >     sink-vdos-v1: [ sink-vdos ]
> > >     sink-vdos: [ sink-vdos-v1 ]
> > > @@ -478,3 +488,16 @@ examples:
> > >               };
> > >           };
> > >       };
> > > +
> > > +  # USB-C connector with PD timers
> > > +  - |
> > > +    #include <dt-bindings/usb/pd.h>
> > > +    usb {
> > > +        connector {
> > > +            compatible = "usb-c-connector";
> > > +            label = "USB-C";
> > > +            pd-timers =
> > > +                <PD_TIMER_SINK_WAIT_CAP 600>,
> > > +                <PD_TIMER_CC_DEBOUNCE 170>;
> > > +        };
> > > +    };
> > > diff --git a/include/dt-bindings/usb/pd.h b/include/dt-bindings/usb/pd.h
> > > index e6526b138174..6c58c30f3f39 100644
> > > --- a/include/dt-bindings/usb/pd.h
> > > +++ b/include/dt-bindings/usb/pd.h
> > > @@ -465,4 +465,12 @@
> > >   	 | ((vbm) & 0x3) << 15 | (curr) << 14 | ((vbi) & 0x3f) << 7	\
> > >   	 | ((gi) & 0x3f) << 1 | (ct))
> > > +/* PD Timer definitions */
> > > +/* tTypeCSinkWaitCap (Table 6-68 Time Values, USB PD3.1 Spec) */
> > > +#define PD_TIMER_SINK_WAIT_CAP		0
> > > +/* tPSSourceOff (Table 6-68 Time Values, USB PD3.1 Spec) */
> > > +#define PD_TIMER_PS_SOURCE_OFF		1
> > > +/* tCCDebounce (Table 4-33 CC Timing, USB Type-C Cable & Connector Spec Rel2.2) */
> > > +#define PD_TIMER_CC_DEBOUNCE		2
> > > +
> > >   #endif /* __DT_POWER_DELIVERY_H */
> > > -- 
> > > 2.46.0.598.g6f2099f65c-goog
> > > 

-- 
With best wishes
Dmitry