Documentation: ACPI: DSD: Document MDIO PHY

Introduce a mechanism based on generic ACPI _DSD device properties
definition [1] to get PHYs registered on a MDIO bus and provide them to
be connected to MAC.

[1] http://www.uefi.org/sites/default/files/resources/_DSD-device-properties-UUID.pdf

Describe properties "phy-handle" and "phy-mode".

Signed-off-by: Calvin Johnson <calvin.johnson@oss.nxp.com>
Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Acked-by: Rafael J. Wysocki <rafael@kernel.org>
Acked-by: Grant Likely <grant.likely@arm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/Documentation/firmware-guide/acpi/dsd/phy.rst b/Documentation/firmware-guide/acpi/dsd/phy.rst
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+.. SPDX-License-Identifier: GPL-2.0
+
+=========================
+MDIO bus and PHYs in ACPI
+=========================
+
+The PHYs on an MDIO bus [1] are probed and registered using
+fwnode_mdiobus_register_phy().
+
+Later, for connecting these PHYs to their respective MACs, the PHYs registered
+on the MDIO bus have to be referenced.
+
+This document introduces two _DSD properties that are to be used
+for connecting PHYs on the MDIO bus [3] to the MAC layer.
+
+These properties are defined in accordance with the "Device
+Properties UUID For _DSD" [2] document and the
+daffd814-6eba-4d8c-8a91-bc9bbf4aa301 UUID must be used in the Device
+Data Descriptors containing them.
+
+phy-handle
+----------
+For each MAC node, a device property "phy-handle" is used to reference
+the PHY that is registered on an MDIO bus. This is mandatory for
+network interfaces that have PHYs connected to MAC via MDIO bus.
+
+During the MDIO bus driver initialization, PHYs on this bus are probed
+using the _ADR object as shown below and are registered on the MDIO bus.
+
+::
+      Scope(\_SB.MDI0)
+      {
+        Device(PHY1) {
+          Name (_ADR, 0x1)
+        } // end of PHY1
+
+        Device(PHY2) {
+          Name (_ADR, 0x2)
+        } // end of PHY2
+      }
+
+Later, during the MAC driver initialization, the registered PHY devices
+have to be retrieved from the MDIO bus. For this, the MAC driver needs
+references to the previously registered PHYs which are provided
+as device object references (e.g. \_SB.MDI0.PHY1).
+
+phy-mode
+--------
+The "phy-mode" _DSD property is used to describe the connection to
+the PHY. The valid values for "phy-mode" are defined in [4].
+
+The following ASL example illustrates the usage of these properties.
+
+DSDT entry for MDIO node
+------------------------
+
+The MDIO bus has an SoC component (MDIO controller) and a platform
+component (PHYs on the MDIO bus).
+
+a) Silicon Component
+This node describes the MDIO controller, MDI0
+---------------------------------------------
+::
+       Scope(_SB)
+       {
+         Device(MDI0) {
+           Name(_HID, "NXP0006")
+           Name(_CCA, 1)
+           Name(_UID, 0)
+           Name(_CRS, ResourceTemplate() {
+             Memory32Fixed(ReadWrite, MDI0_BASE, MDI_LEN)
+             Interrupt(ResourceConsumer, Level, ActiveHigh, Shared)
+              {
+                MDI0_IT
+              }
+           }) // end of _CRS for MDI0
+         } // end of MDI0
+       }
+
+b) Platform Component
+The PHY1 and PHY2 nodes represent the PHYs connected to MDIO bus MDI0
+---------------------------------------------------------------------
+::
+       Scope(\_SB.MDI0)
+       {
+         Device(PHY1) {
+           Name (_ADR, 0x1)
+         } // end of PHY1
+
+         Device(PHY2) {
+           Name (_ADR, 0x2)
+         } // end of PHY2
+       }
+
+DSDT entries representing MAC nodes
+-----------------------------------
+
+Below are the MAC nodes where PHY nodes are referenced.
+phy-mode and phy-handle are used as explained earlier.
+------------------------------------------------------
+::
+       Scope(\_SB.MCE0.PR17)
+       {
+         Name (_DSD, Package () {
+            ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
+                Package () {
+                    Package (2) {"phy-mode", "rgmii-id"},
+                    Package (2) {"phy-handle", \_SB.MDI0.PHY1}
+             }
+          })
+       }
+
+       Scope(\_SB.MCE0.PR18)
+       {
+         Name (_DSD, Package () {
+           ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
+               Package () {
+                   Package (2) {"phy-mode", "rgmii-id"},
+                   Package (2) {"phy-handle", \_SB.MDI0.PHY2}}
+           }
+         })
+       }
+
+References
+==========
+
+[1] Documentation/networking/phy.rst
+
+[2] https://www.uefi.org/sites/default/files/resources/_DSD-device-properties-UUID.pdf
+
+[3] Documentation/firmware-guide/acpi/DSD-properties-rules.rst
+
+[4] Documentation/devicetree/bindings/net/ethernet-controller.yaml