Date:   Thu, 30 Jun 2022 12:11:10 -0400
From:   Sean Anderson <sean.anderson@...o.com>
To:     Rob Herring <robh@...nel.org>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Madalin Bucur <madalin.bucur@....com>, netdev@...r.kernel.org,
        Russell King <linux@...linux.org.uk>,
        Paolo Abeni <pabeni@...hat.com>,
        linux-arm-kernel@...ts.infradead.org,
        Eric Dumazet <edumazet@...gle.com>,
        linux-kernel@...r.kernel.org,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        devicetree@...r.kernel.org
Subject: Re: [PATCH net-next v2 03/35] dt-bindings: net: fman: Add additional
 interface properties

Hi Rob,

On 6/30/22 12:01 PM, Rob Herring wrote:
> On Tue, Jun 28, 2022 at 06:13:32PM -0400, Sean Anderson wrote:
>> At the moment, mEMACs are configured almost completely based on the
>> phy-connection-type. That is, if the phy interface is RGMII, it assumed
>> that RGMII is supported. For some interfaces, it is assumed that the
>> RCW/bootloader has set up the SerDes properly. This is generally OK, but
>> restricts runtime reconfiguration. The actual link state is never
>> reported.
>> 
>> To address these shortcomings, the driver will need additional
>> information. First, it needs to know how to access the PCS/PMAs (in
>> order to configure them and get the link status). The SGMII PCS/PMA is
>> the only currently-described PCS/PMA. Add the XFI and QSGMII PCS/PMAs as
>> well. The XFI (and 1GBase-KR) PCS/PMA is a c45 "phy" which sits on the
>> same MDIO bus as SGMII PCS/PMA. By default they will have conflicting
>> addresses, but they are also not enabled at the same time by default.
>> Therefore, we can let the XFI PCS/PMA be the default when
>> phy-connection-type is xgmii. This will allow for
>> backwards-compatibility.
>> 
>> QSGMII, however, cannot work with the current binding. This is because
>> the QSGMII PCS/PMAs are only present on one MAC's MDIO bus. At the
>> moment this is worked around by having every MAC write to the PCS/PMA
>> addresses (without checking if they are present). This only works if
>> each MAC has the same configuration, and only if we don't need to know
>> the status. Because the QSGMII PCS/PMA will typically be located on a
>> different MDIO bus than the MAC's SGMII PCS/PMA, there is no fallback
>> for the QSGMII PCS/PMA.
>> 
>> mEMACs (across all SoCs) support the following protocols:
>> 
>> - MII
>> - RGMII
>> - SGMII, 1000Base-X, and 1000Base-KX
>> - 2500Base-X (aka 2.5G SGMII)
>> - QSGMII
>> - 10GBase-R (aka XFI) and 10GBase-KR
>> - XAUI and HiGig
>> 
>> Each line documents a set of orthogonal protocols (e.g. XAUI is
>> supported if and only if HiGig is supported). Additionally,
>> 
>> - XAUI implies support for 10GBase-R
>> - 10GBase-R is supported if and only if RGMII is not supported
>> - 2500Base-X implies support for 1000Base-X
>> - MII implies support for RGMII
>> 
>> To switch between different protocols, we must reconfigure the SerDes.
>> This is done by using the standard phys property. We can also use it to
>> validate whether different protocols are supported (e.g. using
>> phy_validate). This will work for serial protocols, but not RGMII or
>> MII. Additionally, we still need to be compatible when there is no
>> SerDes.
>> 
>> While we can detect 10G support by examining the port speed (as set by
>> fsl,fman-10g-port), we cannot determine support for any of the other
>> protocols based on the existing binding. In fact, the binding works
>> against us in some respects, because pcsphy-handle is required even if
>> there is no possible PCS/PMA for that MAC. To allow for backwards-
>> compatibility, we use a boolean-style property for RGMII (instead of
>> presence/absence-style). When the property for RGMII is missing, we will
>> assume that it is supported. The exception is MII, since no existing
>> device trees use it (as far as I could tell).
>> 
>> Unfortunately, QSGMII support will be broken for old device trees. There
>> is nothing we can do about this because of the PCS/PMA situation (as
>> described above).
>> 
>> Signed-off-by: Sean Anderson <sean.anderson@...o.com>
>> ---
>> 
>> Changes in v2:
>> - Better document how we select which PCS to use in the default case
>> 
>>  .../bindings/net/fsl,fman-dtsec.yaml          | 52 +++++++++++++++++--
>>  .../devicetree/bindings/net/fsl-fman.txt      |  5 +-
>>  2 files changed, 51 insertions(+), 6 deletions(-)
>> 
>> diff --git a/Documentation/devicetree/bindings/net/fsl,fman-dtsec.yaml b/Documentation/devicetree/bindings/net/fsl,fman-dtsec.yaml
>> index 809df1589f20..ecb772258164 100644
>> --- a/Documentation/devicetree/bindings/net/fsl,fman-dtsec.yaml
>> +++ b/Documentation/devicetree/bindings/net/fsl,fman-dtsec.yaml
>> @@ -85,9 +85,41 @@ properties:
>>      $ref: /schemas/types.yaml#/definitions/phandle
>>      description: A reference to the IEEE1588 timer
>>  
>> +  phys:
>> +    description: A reference to the SerDes lane(s)
>> +    maxItems: 1
>> +
>> +  phy-names:
>> +    items:
>> +      - const: serdes
>> +
>>    pcsphy-handle:
>> -    $ref: /schemas/types.yaml#/definitions/phandle
>> -    description: A reference to the PCS (typically found on the SerDes)
>> +    $ref: /schemas/types.yaml#/definitions/phandle-array
>> +    minItems: 1
>> +    maxItems: 3
> 
> What determines how many entries?

It depends on what the particular MAC supports. From what I can tell, the following
combinations are valid:

- Neither SGMII, QSGMII, or XFI
- Just SGMII
- Just QSGMII
- SGMII and QSGMII
- SGMII and XFI
- All of SGMII, QSGMII, and XFI

All of these are used on different SoCs.

>> +    description: |
>> +      A reference to the various PCSs (typically found on the SerDes). If
>> +      pcs-names is absent, and phy-connection-type is "xgmii", then the first
>> +      reference will be assumed to be for "xfi". Otherwise, if pcs-names is
>> +      absent, then the first reference will be assumed to be for "sgmii".
>> +
>> +  pcs-names:
>> +    $ref: /schemas/types.yaml#/definitions/string-array
>> +    minItems: 1
>> +    maxItems: 3
>> +    contains:
>> +      enum:
>> +        - sgmii
>> +        - qsgmii
>> +        - xfi
> 
> This means '"foo", "xfi", "bar"' is valid. I think you want to 
> s/contains/items/.
> 
>> +    description: The type of each PCS in pcsphy-handle.
>> +
> 
>> +  rgmii:
>> +    enum: [0, 1]
>> +    description: 1 indicates RGMII is supported, and 0 indicates it is not.
>> +
>> +  mii:
>> +    description: If present, indicates that MII is supported.
> 
> Types? Need vendor prefixes.

OK.

> Are these board specific or SoC specific? Properties are appropriate for 
> the former. The latter case should be implied by the compatible string.

Unfortunately, there are not existing specific compatible strings for each
device in each SoC. I suppose those could be added; however, this basically
reflects how each device is hooked up. E.g. on one SoC a device would be
connected to the RGMII pins, but not on another SoC. The MAC itself still
has hardware support for RGMII, but such a configuration would not function.

--Sean

>>  
>>    tbi-handle:
>>      $ref: /schemas/types.yaml#/definitions/phandle
>> @@ -100,6 +132,10 @@ required:
>>    - fsl,fman-ports
>>    - ptp-timer
>>  
>> +dependencies:
>> +  pcs-names: [pcsphy-handle]
>> +  mii: [rgmii]
>> +
>>  allOf:
>>    - $ref: "ethernet-controller.yaml#"
>>    - if:
>> @@ -117,7 +153,11 @@ allOf:
>>              const: fsl,fman-memac
>>      then:
>>        required:
>> -        - pcsphy-handle
>> +        - rgmii
>> +    else:
>> +      properties:
>> +        rgmii: false
>> +        mii: false
>>  
>>  unevaluatedProperties: false
>>  
>> @@ -138,7 +178,11 @@ examples:
>>              reg = <0xe8000 0x1000>;
>>              fsl,fman-ports = <&fman0_rx_0x0c &fman0_tx_0x2c>;
>>              ptp-timer = <&ptp_timer0>;
>> -            pcsphy-handle = <&pcsphy4>;
>> +            pcsphy-handle = <&pcsphy4>, <&qsgmiib_pcs1>;
>> +            pcs-names = "sgmii", "qsgmii";
>> +            rgmii = <0>;
>>              phy-handle = <&sgmii_phy1>;
>>              phy-connection-type = "sgmii";
>> +            phys = <&serdes1 1>;
>> +            phy-names = "serdes";
>>      };
>> diff --git a/Documentation/devicetree/bindings/net/fsl-fman.txt b/Documentation/devicetree/bindings/net/fsl-fman.txt
>> index b9055335db3b..bda4b41af074 100644
>> --- a/Documentation/devicetree/bindings/net/fsl-fman.txt
>> +++ b/Documentation/devicetree/bindings/net/fsl-fman.txt
>> @@ -320,8 +320,9 @@ For internal PHY device on internal mdio bus, a PHY node should be created.
>>  See the definition of the PHY node in booting-without-of.txt for an
>>  example of how to define a PHY (Internal PHY has no interrupt line).
>>  - For "fsl,fman-mdio" compatible internal mdio bus, the PHY is TBI PHY.
>> -- For "fsl,fman-memac-mdio" compatible internal mdio bus, the PHY is PCS PHY,
>> -  PCS PHY addr must be '0'.
>> +- For "fsl,fman-memac-mdio" compatible internal mdio bus, the PHY is PCS PHY.
>> +  The PCS PHY address should correspond to the value of the appropriate
>> +  MDEV_PORT.
>>  
>>  EXAMPLE
>>  
>> -- 
>> 2.35.1.1320.gc452695387.dirty
>> 
>> 
> 

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