linux-kernel - Re: [PATCH v1 3/9] dt-bindings: reset: intel,rcu-gw: Update bindings for "legacy" SoCs

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Date:   Sun, 3 Jul 2022 01:04:20 +0200
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     Rob Herring <robh@...nel.org>
Cc:     linux-phy@...ts.infradead.org, devicetree@...r.kernel.org,
        p.zabel@...gutronix.de, linux-kernel@...r.kernel.org,
        linux-mips@...r.kernel.org, vkoul@...nel.org, kishon@...com,
        rtanwar@...linear.com
Subject: Re: [PATCH v1 3/9] dt-bindings: reset: intel,rcu-gw: Update bindings
 for "legacy" SoCs

 Hi Rob,

On Fri, Jul 1, 2022 at 6:33 PM Rob Herring <robh@...nel.org> wrote:
>
> On Tue, Jun 28, 2022 at 02:44:35PM +0200, Martin Blumenstingl wrote:
> > The Lantiq Amazon-SE, Danube, xRX100 and xRX200 SoCs have up to two USB2
> > PHYs which are part of the RCU register space. The RCU registers on
> > these SoCs are using big endian. Update the binding for these SoCs to
> > properly describe this IP:
> > - Add compatible strings for Amazon-SE, Danube and xRX100
> > - Rename the xRX200 compatible string (which is not used anywhere) and
> >   switch to the one previously documented in mips/lantiq/rcu.txt
> > - Allow usage of "simple-mfd" and "syscon" in the compatible string so the
> >   child devices (USB2 PHYs) can be described
> > - Allow #address-cells and #size-cells to be set to 1 for describing the
> >   child devices (USB2 PHYs)
> > - #reset-cells must always be 3 (offset, reset bit and status bit) on the
> >   legacy SoCs while LGM uses a fixed value of 2 (offset and reset bit -
> >   status bit is always identical to the reset bit).
> >
> > Signed-off-by: Martin Blumenstingl <martin.blumenstingl@...glemail.com>
> > ---
> >  .../bindings/reset/intel,rcu-gw.yaml          | 84 +++++++++++++++++--
> >  1 file changed, 79 insertions(+), 5 deletions(-)
> >
> > diff --git a/Documentation/devicetree/bindings/reset/intel,rcu-gw.yaml b/Documentation/devicetree/bindings/reset/intel,rcu-gw.yaml
> > index be64f8597710..b90913c7b7d3 100644
> > --- a/Documentation/devicetree/bindings/reset/intel,rcu-gw.yaml
> > +++ b/Documentation/devicetree/bindings/reset/intel,rcu-gw.yaml
> > @@ -11,9 +11,16 @@ maintainers:
> >
> >  properties:
> >    compatible:
> > -    enum:
> > -      - intel,rcu-lgm
> > -      - intel,rcu-xrx200
>
> It is okay to remove/change this because ?
I'll update the description in v2. The "intel,rcu-xrx200" compatible
string isn't used anywhere (upstream or downstream in OpenWrt).
u-boot on Lantiq xRX200 SoCs is too old to pass a dtb to the kernel,
so we're appending the DTB to the kernel image.

> > +    oneOf:
> > +      - items:
> > +          - enum:
> > +              - lantiq,ase-rcu
> > +              - lantiq,danube-rcu
> > +              - lantiq,xrx100-rcu
> > +              - lantiq,xrx200-rcu
> > +          - const: simple-mfd
>
> This says child nodes have 0 dependence on anything in the parent node.
> Such as a clock in the parent needing to be enabled.
>
> > +          - const: syscon
>
> Given the child nodes depend on this, I find the combination to be a
> contradiction. But it's widely used, so oh well.
I can think of two ways to solve this:
1) remove the simple-mfd compatible string and make the driver also
discover child nodes
2) remove the simple-mfd compatible string and remove the USB PHY
child nodes - then add add #phy-cells = <1> to the RCU node itself
(and somehow update the RCU and USB PHY drivers accordingly)
3) introduce a separate child node for the reset-controller, then the
child nodes depend on each other (but there's no strict dependency on
the parent anymore other than the fact that the parent needs a
"syscon" compatible string).

My understanding of this IP block is that it was initially designed as
a reset controller, hence its name "reset controller unit" (RCU). Then
additional logic was added after the fact.
So I think 1) (dropping the simple-mfd compatible string) or 2)
(dropping the simple-mfd compatible string and the child nodes
altogether) is the right way to go here. Which route would you go and
why?

[...]
> > +patternProperties:
> > +  "^usb2-phy@[0-9a-f]+$":
> > +    type: object
> > +    $ref: "../phy/lantiq,xway-rcu-usb2-phy.yaml"
> > +
> > +allOf:
> > +  - if:
> > +      properties:
> > +        compatible:
> > +          contains:
> > +            const: intel,rcu-lgm
> > +    then:
> > +      properties:
> > +        "#reset-cells":
> > +          const: 2
>
> else:
>   properties:
>     "#reset-cells":
>       const: 3
much shorter, thanks - I'll take care of this in v2.

[...]
> > +        usb_phy0: usb2-phy@18 {
> > +            compatible = "lantiq,xrx200-usb2-phy";
> > +            reg = <0x18 4>, <0x38 4>;
> > +            status = "disabled";
>
> Why is your example disabled? Don't use 'status' in examples.
I should know this better - I'll fix this in v2.


Best regards,
Martin