Re: [PATCH v3 1/3] dt-bindings: usb: dwc3: Add support for multiport related properties

[Harsh Agarwal]

On 6/10/2022 10:52 PM, Rob Herring wrote:
> On Fri, Jun 10, 2022 at 05:25:25PM +0530, Harsh Agarwal wrote:
> > On 6/9/2022 9:08 PM, Rob Herring wrote:
> > > On Wed, Jun 08, 2022 at 11:06:25PM +0530, Harsh Agarwal wrote:
> > > > Added support for multiport, mport, num_usb2_phy and num_usb3_phy
> > > > properties. These properties are used to support devices having
> > > > a multiport controller.
> > > >
> > > > Signed-off-by: Harsh Agarwal <quic_harshq@xxxxxxxxxxx>
> > > > ---
> > > >    .../devicetree/bindings/usb/snps,dwc3.yaml         | 53 ++++++++++++++++++++++
> > > >    1 file changed, 53 insertions(+)
> > > >
> > > > diff --git a/Documentation/devicetree/bindings/usb/snps,dwc3.yaml b/Documentation/devicetree/bindings/usb/snps,dwc3.yaml
> > > > index d41265b..9332fa2 100644
> > > > --- a/Documentation/devicetree/bindings/usb/snps,dwc3.yaml
> > > > +++ b/Documentation/devicetree/bindings/usb/snps,dwc3.yaml
> > > > @@ -343,6 +343,32 @@ properties:
> > > >          This port is used with the 'usb-role-switch' property  to connect the
> > > >          dwc3 to type C connector.
> > > > +  multiport:
> > > Again, I don't think this is going to play well if you need to describe
> > > USB devices in your DT. For example, a USB hub with additional DT
> > > properties.
> > Thanks for the review Rob.
> > Can you please explain why would one want to describe a USB hub in device
> > tree ?
> Because someone soldered a hub on the board and then connected extra
> things like resets, GPIOs, supplies which are all outside of standard
> USB. It's quite common...
>
> There's some flavors of Beagle boards that have a USB ethernet on board.
> Guess what, they skipped out on a eeprom and so the device and a MAC
> address has to be described in DT (if you want a stable MAC addr).
>
> > IF USB hub is attached to a root port , it would be enumerated by the SW. I
> > am not clear how DT is coming
> > into picture. Even if there was a scenario to add DT properties for a hub,
> > then this multiport node would be like a nop
> > as it just helps us to get the PHY phandles in a proper way.
> It won't be enumerated by the SW if it has to be powered on first using
> non-standard resources.
>
> > Do you feel we still might have a problem with multiport node ?
> A board design could have a hub or device on any or all your ports.
>
> > > > +    description:
> > > > +      If a single USB controller supports multiple ports, then it's referred to as
> > > > +      a multiport controller. Each port of the multiport controller can support
> > > > +      either High Speed or Super Speed or both and have their own PHY phandles. Each
> > > > +      port is represented by "mport" node and all the "mport" nodes are grouped
> > > > +      together inside the "multiport" node where individual "mport" node defines the
> > > > +      PHYs supported by that port.
> > > > +
> > > > +  num_usb2_phy:
> > > > +    description: Total number of HS-PHYs defined by the multiport controller.
> > > > +    $ref: /schemas/types.yaml#/definitions/uint32
> > > > +
> > > > +  num_usb3_phy:
> > > > +    description: Total number of SS-PHYs defined by the multiport controller.
> > > > +    $ref: /schemas/types.yaml#/definitions/uint32
> > > > +
> > > > +  mport:
> > > > +    description: Each mport node represents one port of the multiport controller.
> > > > +    oneOf:
> > > > +      - required:
> > > > +        - usb-phy
> > > This is deprecated. Why are you adding it?
> > Do you mean "usb-phy" is deprecated ?
> It is replaced by 'phys'. Any new user should use 'phys'.
>
> > Internally we use usb-phy with our downstream GLUE driver
> Upstream does not care about that.
>
> > > > +      - required:
> > > > +        - phys
> > > > +        - phy-names
> > > Other multi port USB hosts just have a list of phys. Why can't you just
> > > use phy-names to identify each phy:
> > >
> > > phy-names = "port0-hs", "port0-ss", "port1-hs", "port1-ss", "port2-hs",
> > >     "port3-hs";
> > With the above method we would have to do some kind of string parsing on the
> > phy-names to get the HS and SS PHYs as we need to cater to different
> > combinations of Ports ( some support HS+SS , other supports SS only).
> You are doing string parsing anyways to get the child nodes and
> properties.
>
> > So one challenge here is with the "usb-phy". There we directly define the
> > phy phandles and that might/might-not have proper sub-strings. eg
> > USB_QMP_PHY . So extracting PHYS could be tricky if the phy-handle does not
> > have proper substring like "SS" "HS" etc.
> The schema can and should enforce that you have the proper strings.
Hi Rob,
Apologies for replying late.

I get your concern. Yes we can remove the "multiport" node and instead 
define the
USB phy phandles all in one place. Still I would need to add support for 
both generic-phy and
usb-phy framework as downstream many vendors are using "usb-phy" and 
it's supported by ACK as well.
This would not regress anything with Generic PHY.

@Greg can you please comment as ACK has support for usb-phy framework.

Now coming to implementation, let's consider a 4 port USB multiport 
controller having
4 HS PHYs and 2 SS PHYs.  We can have two approaches here

#1 -> If we could mandate using "HS" or "SS" as substring in
phy-names or usb-phy, then we can calculate number of HS and SS phy and 
also get
corresponding PHY nodes. Only concern here is that downstream vendors 
might need
to change their existing usb-phy names and add proper substring if they 
are not doing so ;

phy = <&usb-hs-phy>,<&usb-ss-phy>,
      <&usb-hs-phy1>, <&usb-ss-phy1>,
      <&usb-hs-phy2>, <&usb-hs-phy3>;

phy-names = "port0-hs", "port0-ss", "port1-hs", "port1-ss", "port2-hs",
   "port3-hs";


OR


#2-> We could mandate defining the USB phy in HS - SS pairs.
For ports that has only HS PHY, we would need to define usb_nop_phy in 
SS place.
Then we can calculate the number of HS & SS phys and get corresponding
PHY nodes by using simple fact that HS phy would be defined at odd places &
SS phy defined at even. Here substrings are not mandated.

phy = <&usb-hs-phy>,<&usb-qmp-phy>,
      <&usb-hs-phy1>, <&usb-qmp-phy1>,
      <&usb-hs-phy2>, <&usb_nop_phy>
      <&usb-hs-phy3>, <&usb_nop_phy>;

phy-names = "port0-hs", "port0-ss",
	    "port1-hs", "port1-ss",
	    "port2-hs", "usb-nop",
	    "port3-hs", "usb-nop";


Please let me know if you prefer any approach here or have any suggestions.

>   
>
> > We cannot break existing implementation and so we thought of going with the
> > "multiport" node approach, listing below some flexibility :
> How would this break?
>
> > 1. Better representation of the PHYs and it's relation with a port.
> > 2. Here for each port we pick the first PHY as HS and 2nd PHY as SS as we
> > have been doing traditionally.
> > So for "usb-phy" we need not care how the PHY handles are named.
> >
> > 3. It's future proof incase we need to add additional properties specific to
> > a port. We can just add those properties inside MP_1 or MP_2 etc.
> > Though nothing like this has yet been implemented.
> Then you have to consider how the standard USB device binding fits into
> this, and it needs to work for anyone with multiple ports. The
> usb-hcd.yaml schema already defines that child nodes represent a USB
> device attached to a port on the host. 'reg' is the port number.
>
> Rob