Subject: Re: [PATCH net-next v2 01/35] dt-bindings: phy: Add QorIQ SerDes binding

From: Rob Herring <[email-masked]>
Date: Thu, 30 Jun 2022 11:27:13 -0600

On Tue, Jun 28, 2022 at 06:13:30PM -0400, Sean Anderson wrote:
> This adds a binding for the SerDes module found on QorIQ processors. The
> phy reference has two cells, one for the first lane and one for the
> last. This should allow for good support of multi-lane protocols when
> (if) they are added. There is no protocol option, because the driver is
> designed to be able to completely reconfigure lanes at runtime.
> Generally, the phy consumer can select the appropriate protocol using
> set_mode. For the most part there is only one protocol controller
> (consumer) per lane/protocol combination. The exception to this is the
> B4860 processor, which has some lanes which can be connected to
> multiple MACs. For that processor, I anticipate the easiest way to
> resolve this will be to add an additional cell with a "protocol
> controller instance" property.
> 
> Each serdes has a unique set of supported protocols (and lanes). The
> support matrix is stored in the driver and is selected based on the
> compatible string. It is anticipated that a new compatible string will
> need to be added for each serdes on each SoC that drivers support is
> added for. There is no "generic" compatible string for this reason.
> 
> There are two PLLs, each of which can be used as the master clock for
> each lane. Each PLL has its own reference. For the moment they are
> required, because it simplifies the driver implementation. Absent
> reference clocks can be modeled by a fixed-clock with a rate of 0.
> 
> Signed-off-by: Sean Anderson <[email-masked]>
> ---
> 
> Changes in v2:
> - Add #clock-cells. This will allow using assigned-clocks* to configure
>   the PLLs.
> - Allow a value of 1 for phy-cells. This allows for compatibility with
>   the similar (but according to Ioana Ciornei different enough) lynx-28g
>   binding.
> - Document phy cells in the description
> - Document the structure of the compatible strings
> - Fix example binding having too many cells in regs
> - Move compatible first
> - Refer to the device in the documentation, rather than the binding
> - Remove minItems
> - Rename to fsl,lynx-10g.yaml
> - Use list for clock-names
> 
>  .../devicetree/bindings/phy/fsl,lynx-10g.yaml | 93 +++++++++++++++++++
>  1 file changed, 93 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/phy/fsl,lynx-10g.yaml
> 
> diff --git a/Documentation/devicetree/bindings/phy/fsl,lynx-10g.yaml b/Documentation/devicetree/bindings/phy/fsl,lynx-10g.yaml
> new file mode 100644
> index 000000000000..b5a6f631df9f
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/phy/fsl,lynx-10g.yaml
> @@ -0,0 +1,93 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +$id: http://devicetree.org/schemas/phy/fsl,lynx-10g.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: NXP Lynx 10G SerDes
> +
> +maintainers:
> +  - Sean Anderson <[email-masked]>
> +
> +description: |
> +  These Lynx "SerDes" devices are found in NXP's QorIQ line of processors. The
> +  SerDes provides up to eight lanes. Each lane may be configured individually,
> +  or may be combined with adjacent lanes for a multi-lane protocol. The SerDes
> +  supports a variety of protocols, including up to 10G Ethernet, PCIe, SATA, and
> +  others. The specific protocols supported for each lane depend on the
> +  particular SoC.
> +
> +properties:
> +  compatible:
> +    description: |
> +      Each compatible is of the form "fsl,<soc-name>-serdes-<instance>".
> +      Although many registers are compatible between different SoCs, the
> +      supported protocols and lane assignments tend to be unique to each SerDes.
> +      Additionally, the method of activating protocols may also be unique.

We typically have properties for handling these variables. Numbering 
instances is something we avoid.

> +      Because of this, each SerDes instance will need its own compatible string.

> +      In cases where two SoCs share the same SerDes implementation (such as the
> +      LS1046A and LS1026A), both SoCs should share the same compatible strings.

No, not unless the 2 parts are just fuse or package pinout differences. 
Otherwise, there's always the chance they are not 'the same' and have 
different bugs.

You could have "fsl,ls1046a-serdes", "fsl,ls1026a-serdes" (whichever SoC 
is older last) if you think they are 'the same'.

> +    enum:
> +      - fsl,ls1046a-serdes-1
> +      - fsl,ls1046a-serdes-2
> +
> +  "#clock-cells":
> +    const: 1
> +    description: |
> +      The cell contains the index of the PLL, starting from 0. Note that when
> +      assigning a rate to a PLL, the PLLs' rates are divided by 1000 to avoid
> +      overflow. A rate of 5000000 corresponds to 5GHz.
> +
> +  "#phy-cells":
> +    minimum: 1
> +    maximum: 2
> +    description: |
> +      The cells contain the following arguments:
> +      - The first lane in the group. Lanes are numbered based on the register
> +        offsets, not the I/O ports. This corresponds to the letter-based ("Lane
> +        A") naming scheme, and not the number-based ("Lane 0") naming scheme. On
> +        most SoCs, "Lane A" is "Lane 0", but not always.
> +      - Last lane. For single-lane protocols, this should be the same as the
> +        first lane.
> +      If no lanes in a SerDes can be grouped, then #phy-cells may be 1, and the
> +      first cell will specify the only lane in the group.

Usually when we have per lane phys, the consumer side will have a 'phys' 
entry per lane.

Having a variable number of cells isn't great either. We usually only do 
that when we have to extend an existing binding.

> +
> +  clocks:
> +    maxItems: 2
> +    description: |
> +      Clock for each PLL reference clock input.
> +
> +  clock-names:
> +    items:
> +      - enum: &clocks
> +          - ref0
> +          - ref1
> +      - enum: *clocks

Whoa, there's a first. Don't use YAML anchors and references. We only 
support JSON subset of YAML.

> +
> +  reg:
> +    maxItems: 1
> +
> +required:
> +  - "#clock-cells"
> +  - "#phy-cells"
> +  - compatible
> +  - clocks
> +  - clock-names
> +  - reg
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    serdes1: phy@1ea0000 {
> +      #clock-cells = <1>;
> +      #phy-cells = <2>;
> +      compatible = "fsl,ls1046a-serdes-1";
> +      reg = <0x1ea0000 0x2000>;
> +      clocks = <&clk_100mhz>, <&clk_156mhz>;
> +      clock-names = "ref0", "ref1";
> +      assigned-clocks = <&serdes1 0>;
> +      assigned-clock-rates = <5000000>;
> +    };
> +
> +...
> -- 
> 2.35.1.1320.gc452695387.dirty
> 
>