linux-kernel - Re: [PATCH net-next v2 3/4] dt-bindings: net: Add RGMII internal delay for DP83869

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Date:   Wed, 20 May 2020 22:44:23 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Dan Murphy <dmurphy@...com>
Cc:     Florian Fainelli <f.fainelli@...il.com>, hkallweit1@...il.com,
        davem@...emloft.net, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH net-next v2 3/4] dt-bindings: net: Add RGMII internal
 delay for DP83869

> I think adding it in the core would be a bit of a challenge.  I think each
> PHY driver needs to handle parsing and validating this property on its own
> (like fifo-depth).  It is a PHY specific setting.

fifo-depth yes. But some delays follow a common pattern.

e.g.
Documentation/devicetree/bindings/net/micrel-ksz90x1.txt

Device Tree Value     Delay   Pad Skew Register Value
  -----------------------------------------------------
        0               -840ps          0000
        200             -720ps          0001
        400             -600ps          0010
        600             -480ps          0011
        800             -360ps          0100
        1000            -240ps          0101
        1200            -120ps          0110
        1400               0ps          0111
        1600             120ps          1000
        1800             240ps          1001
        2000             360ps          1010
        2200             480ps          1011
        2400             600ps          1100
        2600             720ps          1101
        2800             840ps          1110
        3000             960ps          1111

Documentation/devicetree/bindings/net/adi,adin.yaml

 adi,rx-internal-delay-ps:
    description: |
      RGMII RX Clock Delay used only when PHY operates in RGMII mode with
      internal delay (phy-mode is 'rgmii-id' or 'rgmii-rxid') in pico-seconds.
    enum: [ 1600, 1800, 2000, 2200, 2400 ]
    default: 2000

  adi,tx-internal-delay-ps:
    description: |
      RGMII TX Clock Delay used only when PHY operates in RGMII mode with
      internal delay (phy-mode is 'rgmii-id' or 'rgmii-txid') in pico-seconds.
    enum: [ 1600, 1800, 2000, 2200, 2400 ]
    default: 2000

Documentation/devicetree/bindings/net/apm-xgene-enet.txt

- tx-delay: Delay value for RGMII bridge TX clock.
            Valid values are between 0 to 7, that maps to
            417, 717, 1020, 1321, 1611, 1913, 2215, 2514 ps
            Default value is 4, which corresponds to 1611 ps
- rx-delay: Delay value for RGMII bridge RX clock.
            Valid values are between 0 to 7, that maps to
            273, 589, 899, 1222, 1480, 1806, 2147, 2464 ps
            Default value is 2, which corresponds to 899 ps

You could implement checking against a table of valid values, which is
something you need for your PHY. You could even consider making it a
2D table, and return the register value, not the delay?

	  Andrew