PHY polarity inversion via generic device tree properties

Introduce "rx-polarity" and "tx-polarity" device tree properties.
Convert two existing networking use cases - the EN8811H Ethernet PHY and
the Mediatek LynxI PCS.

Requested merge strategy:
Patches 1-5 through linux-phy
linux-phy provides stable branch or tag to netdev
patches 6-10 through netdev

v2 at:
https://lore.kernel.org/netdev/20260103210403.438687-1-vl...
Changes since v2:
- fix bug with existing fwnode which is missing polarity properties.
  This is supposed to return the default value, not an error. (thanks to
  Bjørn Mork).
- fix inconsistency between PHY_COMMON_PROPS and GENERIC_PHY_COMMON_PROPS
  Kconfig options by using PHY_COMMON_PROPS everywhere (thanks to Bjørn
  Mork).

v1 at:
https://lore.kernel.org/netdev/20251122193341.332324-1-vl...
Changes since v1:
- API changes: split error code from returned value; introduce two new
  helpers for simple driver cases
- Add KUnit tests
- Bug fixes in core code and in drivers
- Defer XPCS patches for later (*)
- Convert Mediatek LynxI PCS
- Logical change: rx-polarity and tx-polarity refer to the currently
  described block, and not necessarily to device pins
- Apply Rob's feedback
- Drop the "joint maintainership" idea.

(*) To simplify the generic XPCS driver, I've decided to make
"tx-polarity" default to <PHY_POL_NORMAL>, rather than <PHY_POL_NORMAL>
OR <PHY_POL_INVERT> for SJA1105. But in order to avoid breakage, it
creates a hard dependency on this patch set being merged *first*:
https://lore.kernel.org/netdev/20251118190530.580267-1-vl...
so that the SJA1105 driver can provide an XPCS fwnode with the right
polarity specified. All patches in context can be seen at:
https://github.com/vladimiroltean/linux/tree/phy-polarity...

Original cover letter:

Polarity inversion (described in patch 4/10) is a feature with at least
4 potential new users waiting for a generic description:
- Horatiu Vultur with the lan966x SerDes
- Daniel Golle with the MaxLinear GSW1xx switches
- Bjørn Mork with the AN8811HB Ethernet PHY
- Me with a custom SJA1105 board, switch which uses the DesignWare XPCS

I became interested in exploring the problem space because I was averse
to the idea of adding vendor-specific device tree properties to describe
a common need.

This set contains an implementation of a generic feature that should
cater to all known needs that were identified during my documentation
phase.

Apart from what is converted here, we also have the following, which I
did not touch:
- "st,px_rx_pol_inv" - its binding is a .txt file and I don't have time
  for such a large detour to convert it to dtschema.
- "st,pcie-tx-pol-inv" and "st,sata-tx-pol-inv" - these are defined in a
  .txt schema but are not implemented in any driver. My verdict would be
  "delete the properties" but again, I would prefer not introducing such
  dependency to this series.

Vladimir Oltean (10):
  dt-bindings: phy: rename transmit-amplitude.yaml to
    phy-common-props.yaml
  dt-bindings: phy-common-props: create a reusable "protocol-names"
    definition
  dt-bindings: phy-common-props: ensure protocol-names are unique
  dt-bindings: phy-common-props: RX and TX lane polarity inversion
  phy: add phy_get_rx_polarity() and phy_get_tx_polarity()
  dt-bindings: net: airoha,en8811h: deprecate "airoha,pnswap-rx" and
    "airoha,pnswap-tx"
  net: phy: air_en8811h: deprecate "airoha,pnswap-rx" and
    "airoha,pnswap-tx"
  dt-bindings: net: pcs: mediatek,sgmiisys: deprecate "mediatek,pnswap"
  net: pcs: pcs-mtk-lynxi: pass SGMIISYS OF node to PCS
  net: pcs: pcs-mtk-lynxi: deprecate "mediatek,pnswap"

 .../bindings/net/airoha,en8811h.yaml          |  11 +-
 .../bindings/net/pcs/mediatek,sgmiisys.yaml   |   7 +-
 .../bindings/phy/phy-common-props.yaml        | 157 +++++++
 .../bindings/phy/transmit-amplitude.yaml      | 103 -----
 MAINTAINERS                                   |  10 +
 drivers/net/dsa/mt7530-mdio.c                 |   4 +-
 drivers/net/ethernet/mediatek/mtk_eth_soc.c   |  19 +-
 drivers/net/pcs/Kconfig                       |   1 +
 drivers/net/pcs/pcs-mtk-lynxi.c               |  63 ++-
 drivers/net/phy/Kconfig                       |   1 +
 drivers/net/phy/air_en8811h.c                 |  53 ++-
 drivers/phy/Kconfig                           |  22 +
 drivers/phy/Makefile                          |   2 +
 drivers/phy/phy-common-props-test.c           | 422 ++++++++++++++++++
 drivers/phy/phy-common-props.c                | 209 +++++++++
 include/dt-bindings/phy/phy.h                 |   4 +
 include/linux/pcs/pcs-mtk-lynxi.h             |   5 +-
 include/linux/phy/phy-common-props.h          |  32 ++
 18 files changed, 979 insertions(+), 146 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/phy/phy-common-props.yaml
 delete mode 100644 Documentation/devicetree/bindings/phy/transmit-amplitude.yaml
 create mode 100644 drivers/phy/phy-common-props-test.c
 create mode 100644 drivers/phy/phy-common-props.c
 create mode 100644 include/linux/phy/phy-common-props.h

-- 
2.43.0