Re: [PATCH v9 05/15] dt-bindings: connector: Add property to set initial current cap for FRS

[Badhri Jagan Sridharan <badhri@google.com>]

On Tue, Oct 6, 2020 at 11:29 AM Rob Herring <robh@kernel.org> wrote:
>
> On Mon, Sep 28, 2020 at 07:39:54PM -0700, Badhri Jagan Sridharan wrote:
> > This change adds frs-typec-current which allows setting the initial current
> > capability of the new source when vSafe5V is applied during PD3.0
> > sink Fast Role Swap.
>
> Shouldn't you Cc the person you copied this from?
Not sure whether I get this comment. The patch wasn't copied. Maybe you were
expecting me to CC amelie.delaunay@st.com ? if so, just now CC'ed.

>
>
> > Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
> > ---
> > Changes since v1:
> > - Changing patch version to v6 to fix version number confusion.
> >
> > Changes since v6:
> > - Removed the redundant usb-connector.txt that I created by mistake.
> > - Moved to yaml.
> >
> > Changes since v7:
> > - Rebase
> >
> > Changes since v8:
> > - Redefine new-source-frs-typec-current as string enums to address
> >   Rob Herring's comment.
> > ---
> >  .../bindings/connector/usb-connector.yaml     | 26 +++++++++++++++++++
> >  include/dt-bindings/usb/pd.h                  | 10 +++++++
> >  2 files changed, 36 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/connector/usb-connector.yaml b/Documentation/devicetree/bindings/connector/usb-connector.yaml
> > index 9bd52e63c935..0b8cd08a8678 100644
> > --- a/Documentation/devicetree/bindings/connector/usb-connector.yaml
> > +++ b/Documentation/devicetree/bindings/connector/usb-connector.yaml
> > @@ -142,6 +142,32 @@ properties:
> >      required:
> >        - port@0
> >
> > +  new-source-frs-typec-current:
> > +    description: Initial current capability of the new source when vSafe5V
> > +      is applied during PD3.0 Fast Role Swap. "Table 6-14 Fixed Supply PDO - Sink"
> > +      of "USB Power Delivery Specification Revision 3.0, Version 1.2" provides the
> > +      different power levels and "6.4.1.3.1.6 Fast Role Swap USB Type-C Current"
> > +      provides a detailed description of the field. The sink PDO from current source
> > +      reflects the current source's(i.e. transmitter of the FRS signal) power
> > +      requirement during fr swap. The current sink (i.e. receiver of the FRS signal),
> > +      a.k.a new source, should check if it will be able to satisfy the current source's,
> > +      new sink's, requirement during frswap before enabling the frs signal reception.
> > +      This property refers to maximum current capability that the current sink can
> > +      satisfy. During FRS, VBUS voltage is at 5V, as the partners are in implicit
> > +      contract, hence, the power level is only a function of the current capability.
> > +      "not-supported" implies sink to source fast role swap not supported.
> > +      "default" refers to default USB power level as described by
> > +      "Table 6-14 Fixed Supply PDO - Sink".
> > +      "1.5A" refers to 1.5A@5V.
> > +      "3.0A" refers to 3.0A@5V.
>
>
> > +
> > +    $ref: /schemas/types.yaml#/definitions/string
> > +    enum:
> > +      - not-supported
> > +      - default
> > +      - 1.5A
> > +      - 3.0A
>
> What happens if the property is not present?

The behavior would be the same as "not-supported".

>
> I'm not crazy about mixing strings and what could be a number.

v8 version[1] of the patch was using uint32. I moved to using strings
as you were asking to unify with the approach in [2]. Since [3] was using
string enums, I moved to that. I don't have a strong preference here, so
I can move back to using u32 if you feel so.

[1] https://lore.kernel.org/linux-usb/20200921195555.1050731-5-badhri@google.com/
[2] https://lore.kernel.org/linux-usb/CAPTae5+Pe1m=TUhmPJY91eJbP+B6UroqBo3u7m0AC8YS1WPu9g@mail.gmail.com/
[3] https://lore.kernel.org/linux-arm-kernel/20200902075707.9052-2-amelie.delaunay@st.com/

>
> > +
> >  required:
> >    - compatible
> >
> > diff --git a/include/dt-bindings/usb/pd.h b/include/dt-bindings/usb/pd.h
> > index 985f2bbd4d24..db1ad4532197 100644
> > --- a/include/dt-bindings/usb/pd.h
> > +++ b/include/dt-bindings/usb/pd.h
> > @@ -35,6 +35,16 @@
> >
> >  #define VSAFE5V 5000 /* mv units */
> >
> > +/*
> > + * Based on "Table 6-14 Fixed Supply PDO - Sink" of "USB Power Delivery Specification Revision 3.0,
> > + * Version 1.2"
> > + * Initial current capability of the new source when vSafe5V is applied.
> > + */
> > +#define FRS_NOT_SUPPORTED    0
> > +#define FRS_DEFAULT_POWER    1
> > +#define FRS_5V_1P5A          2
> > +#define FRS_5V_3A            3
>
> Why are these in a DT header, but not used by the binding? Though
This is a mistake on my part. v8 of the patch which had
new-source-frs-typec-current
defined as uint32 were making use of these constants. Now that
new-source-frs-typec-current
is a string, these constants dont have any more significance in the binding.
Will remove in the next version of the patch.

> perhaps they should be. Are these numbers from the spec or made up?
Yes they are from the spec and are from "Table 6-14 Fixed Supply PDO - Sink"
of "USB Power Delivery Specification Revision 3.0, Version 1.2". Not made up.

>
> > +
> >  #define PDO_BATT_MAX_VOLT_SHIFT      20      /* 50mV units */
> >  #define PDO_BATT_MIN_VOLT_SHIFT      10      /* 50mV units */
> >  #define PDO_BATT_MAX_PWR_SHIFT       0       /* 250mW units */
> > --
> > 2.28.0.709.gb0816b6eb0-goog
> >