net: dsa: felix: Add PCS operations for PHYLINK

net: dsa: felix: Add PCS operations for PHYLINK

Layerscape SoCs traditionally expose the SerDes configuration/status for
Ethernet protocols (PCS for SGMII/USXGMII/10GBase-R etc etc) in a register
format that is compatible with clause 22 or clause 45 (depending on
SerDes protocol). Each MAC has its own internal MDIO bus on which there
is one or more of these PCS's, responding to commands at a configurable
PHY address. The per-port internal MDIO bus (which is just for PCSs) is
totally separate and has nothing to do with the dedicated external MDIO
controller (which is just for PHYs), but the register map for the MDIO
controller is the same.

The VSC9959 (Felix) switch instantiated in the LS1028A is integrated
in hardware with the ENETC PCS of its DSA master, and reuses its MDIO
controller driver, so Felix has been made to depend on it in Kconfig.

 +------------------------------------------------------------------------+
 |                   +--------+ GMII (typically disabled via RCW)         |
 | ENETC PCI         |  ENETC |--------------------------+                |
 | Root Complex      | port 3 |-----------------------+  |                |
 | Integrated        +--------+                       |  |                |
 | Endpoint                                           |  |                |
 |                   +--------+ 2.5G GMII             |  |                |
 |                   |  ENETC |--------------+        |  |                |
 |                   | port 2 |-----------+  |        |  |                |
 |                   +--------+           |  |        |  |                |
 |                                     +--------+  +--------+             |
 |                                     |  Felix |  |  Felix |             |
 |                                     | port 4 |  | port 5 |             |
 |                                     +--------+  +--------+             |
 |                                                                        |
 | +--------+  +--------+  +--------+  +--------+  +--------+  +--------+ |
 | |  ENETC |  |  ENETC |  |  Felix |  |  Felix |  |  Felix |  |  Felix | |
 | | port 0 |  | port 1 |  | port 0 |  | port 1 |  | port 2 |  | port 3 | |
 +------------------------------------------------------------------------+
 |    ||||  SerDes |          ||||        ||||        ||||        ||||    |
 | +--------+block |       +--------------------------------------------+ |
 | |  ENETC |      |       |       ENETC port 2 internal MDIO bus       | |
 | | port 0 |      |       |  PCS         PCS          PCS        PCS   | |
 | |   PCS  |      |       |   0           1            2          3    | |
 +-----------------|------------------------------------------------------+
        v          v           v           v            v          v
     SGMII/      RGMII    QSGMII/QSXGMII/4xSGMII/4x1000Base-X/4x2500Base-X
    USXGMII/   (bypasses
  1000Base-X/   SerDes)
  2500Base-X

In the LS1028A SoC described above, the VSC9959 Felix switch is PF5 of
the ENETC root complex, and has 2 BARs:
- BAR 4: the switch's effective registers
- BAR 0: the MDIO controller register map lended from ENETC port 2
         (PF2), for accessing its associated PCS's.

This explanation is necessary because the patch does some renaming
"pci_bar" -> "switch_pci_bar" for clarity, which would otherwise appear
a bit obtuse.

The fact that the internal MDIO bus is "borrowed" is relevant because
the register map is found in PF5 (the switch) but it triggers an access
fault if PF2 (the ENETC DSA master) is not enabled. This is not treated
in any way (and I don't think it can be treated).

All of this is so SoC-specific, that it was contained as much as
possible in the platform-integration file felix_vsc9959.c.

We need to parse and pre-validate the device tree because of 2 reasons:
- The PHY mode (SerDes protocol) cannot change at runtime due to SoC
  design.
- There is a circular dependency in that we need to know what clause the
  PCS speaks in order to find it on the internal MDIO bus. But the
  clause of the PCS depends on what phy-mode it is configured for.

The goal of this patch is to make steps towards removing the bootloader
dependency for SGMII PCS pre-configuration, as well as to add support
for monitoring the in-band SGMII AN between the PCS and the system-side
link partner (PHY or other MAC).

In practice the bootloader dependency is not completely removed. U-Boot
pre-programs the PHY address at which each PCS can be found on the
internal MDIO bus (MDEV_PORT). This is needed because the PCS of each
port has the same out-of-reset PHY address of zero. The SerDes register
for changing MDEV_PORT is pretty deep in the SoC (outside the addresses
of the ENETC PCI BARs) and therefore inaccessible to us from here.

Felix VSC9959 and Ocelot VSC7514 are integrated very differently in
their respective SoCs, and for that reason Felix does not use the Ocelot
core library for PHYLINK. On one hand we don't want to impose the
fixed phy-mode limitation to Ocelot, and on the other hand Felix doesn't
need to force the MAC link speed the way Ocelot does, since the MAC is
connected to the PCS through a fixed GMII, and the PCS is the one who
does the rate adaptation at lower link speeds, which the MAC does not
even need to know about. In fact changing the GMII speed for Felix
irrecoverably breaks transmission through that port until a reset.

The pair with ENETC port 3 and Felix port 5 is optional and doesn't
support tagging. When we enable it, swp5 is a regular slave port, albeit
an internal one. The trouble is that it doesn't work, and that is
because the DSA PHYLIB adaptation layer doesn't treat fixed-link slave
ports. So that is yet another reason for wanting to convert Felix to the
native PHYLINK API.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>