Re: [PATCH devicetree 2/2] dt-bindings: phy: Add `tx-amplitude-microvolt` property binding
From: Rob Herring <robh@kernel.org>
Date: 2021-12-15 21:58:47
Also in:
linux-phy, netdev
On Wed, Dec 15, 2021 at 12:34:32AM +0100, Marek Behún wrote:
Common PHYs often have the possibility to specify peak-to-peak voltage on the differential pair - the default voltage sometimes needs to be changed for a particular board.
I can envision needing this, but I can't say that I've seen custom properties being proposed for this purpose.
Add properties `tx-amplitude-microvolt` and `tx-amplitude-microvolt-names` for this purpose. The second property is needed to specify
Is the amplitude peak to peak? You just said it was, but perhaps make the property name more clearly defined: tx-p2p-microvolt
Example usage with only one voltage (it will be used for all supported PHY modes, the `tx-amplitude-microvolt-names` property is not needed in this case): tx-amplitude-microvolt = <915000>; Example usage with voltages for multiple modes: tx-amplitude-microvolt = <915000>, <1100000>, <1200000>; tx-amplitude-microvolt-names = "2500base-x", "usb", "pcie";
I'm not wild about the -names, but I think outside of ethernet most cases will only be 1 entry. For a phy provider with multiple phys, what if each one needs a different voltage (for the same mode)?
Signed-off-by: Marek Behún <kabel@kernel.org>
---
I wanted to constrain the values allowed in the
`tx-amplitude-microvolt-names` property to:
- ethernet SerDes modes (sgmii, qsgmii, 10gbase-r, 2500base-x, ...)
- PCIe modes (pattern: ^pcie[1-6]?$)
- USB modes (pattern: ^usb((-host|-device|-otg)?-(ls|fs|hs|ss|ss\+|4))?$)
- DisplayPort modes (pattern: ^dp(-rbr|-hbr[23]?|-uhbr-(10|13.5|20))?$)
- Camera modes (mipi-dphy, mipi-dphy-univ, mipi-dphy-v2.5-univ)
- Storage modes (sata, ufs-hs, ufs-hs-a, ufs-hs-b)
But was unable to. The '-names' suffix implies string-array type, and
string-array type does not allow to specify a type for all items in a
simple way, i.e.:
items:
enum:
- sgmii
- sata
- usb
...Works here: Documentation/devicetree/bindings/arm/samsung/pmu.yaml:56 The requirement is you need to constrain the size with maxItems. It can be a 'should be enough for anyone' value.
quoted hunk ↗ jump to hunk
Such constraint does work when changing ethernet controller's `phy-connection-type` to array, see https://lore.kernel.org/netdev/20211123164027.15618-2-kabel@kernel.org/ (local) But it seems that string-array type prohibits this. --- .../devicetree/bindings/phy/phy.yaml | 22 +++++++++++++++++++ 1 file changed, 22 insertions(+)diff --git a/Documentation/devicetree/bindings/phy/phy.yaml b/Documentation/devicetree/bindings/phy/phy.yaml index a5b6b04cff5b..8915065cf6c2 100644 --- a/Documentation/devicetree/bindings/phy/phy.yaml +++ b/Documentation/devicetree/bindings/phy/phy.yaml@@ -31,9 +31,29 @@ properties: Phandle to a regulator that provides power to the PHY. This regulator will be managed during the PHY power on/off sequence. + tx-amplitude-microvolt: + description: + Transmit amplitude voltages in microvolts, peak-to-peak. If this property + contains multiple values for various PHY modes, the + 'tx-amplitude-microvolt-names' property must be provided and contain + corresponding mode names. + + tx-amplitude-microvolt-names: + description: | + Names of the modes corresponding to voltages in the + 'tx-amplitude-microvolt' property. Required only if multiple voltages + are provided. + + If a value of 'default' is provided, the system should use it for any PHY + mode that is otherwise not defined here. If 'default' is not provided, the + system should use manufacturer default value. + required: - '#phy-cells' +dependencies: + tx-amplitude-microvolt-names: [ tx-amplitude-microvolt ] + additionalProperties: true examples:@@ -46,6 +66,8 @@ examples: phy: phy { #phy-cells = <1>; phy-supply = <&phy_regulator>; + tx-amplitude-microvolt = <915000>, <1100000>, <1200000>; + tx-amplitude-microvolt-names = "2500base-x", "usb-hs", "usb-ss"; }; ethernet-controller {-- 2.32.0