net: phy: add X-Powers AC200/AC300 EPHY driver

The AC200 and AC300 contain compatible Fast Ethernet link PHYs, but the
link endpoint is inaccessible until package-specific control registers
have pow

net: phy: add X-Powers AC200/AC300 EPHY driver

The AC200 and AC300 contain compatible Fast Ethernet link PHYs, but the
link endpoint is inaccessible until package-specific control registers
have powered and configured it.

Add one PHY driver which binds the link child and joins its parent
Ethernet PHY package. Fixed package compatibles select the corresponding
backend. The generic ACx00 compatible reads one packed configuration field
and selects the backend before touching backend-specific resources. The
AC300 path therefore does not resolve or access the candidate AC200 I2C
device.

Require two returned NVMEM bytes for AC300 and selectable ACx00
packages before selecting the backend. Keep the existing little-endian
decoding and one-byte calibration support for fixed AC200 packages.

AC200 locates the I2C device referenced by the package and establishes a
managed device link. It verifies that the provider is fully bound under
the supplier device lock before retrieving the regmap attached to the I2C
device. The companion MFD provider enables and exclusively pins the input
clock rate while it is bound. The link keeps the supplier bound until the
PHY consumer has unbound. Firmware must make the selected AC200 provider
path available before the PHY probes.

AC300 uses the PHY package helpers to access the control range at base
address plus 16. Keeping both backends in the same module lets the common
link implementation own the complete PHY without registering artificial
control devices.

Obtain and manage the selected package supply and calibration, manage the
AC300 input clock, validate or program the link address, and apply the
required reset, clock, I/O and shutdown sequences. Start in the
hardware-default MII mode so the forced PHY device can probe before a MAC
attaches, then apply the MAC-provided MII or RMII mode before the normal
PHY soft reset. AC200 specifies no additional delay between its EPHY
controls; the provider's input-clock startup delay is already complete
before its regmap becomes available.

Apply the common vendor analog initialization, optional AC300
low-calibration tuning and board-selected receive-clock inversion. Keep
MDI/MDI-X in automatic mode. Preserve standard MAC-managed EEE support
while disabling the vendor PHY-autonomous Intelligent EEE mode. Restart
autonegotiation when restoring the standard EEE advertisement changes it.

Serialize package state and the multi-register power sequences across the
different phylib callback lock contexts. Power down the package control
block and its supply during PHY suspend, then restore them and the vendor
configuration during resume. If shutdown fails after resetting the PHY,
restore the vendor settings and standard advertisement or forced
speed/duplex under the phylib lock before returning the original error.
A failed suspend is not followed by a normal resume to restore these
settings. Power down again if recovery fails, and unwind package power if
reset, resume or configuration fails after power-on.

Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
Link: https://patch.msgid.link/20260909-submit-acx00-of-dynamic-v1-v11-2-eb45e89ef918@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

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