vendorcode/google/chromeos: Support MAC address passthru policy

This change adds support for providing a MAC address that can be used
by the OS network drivers to change the MAC address that a NIC uses.

The Realtek r8152 driver in the Linux kernel supports a MAC address
passthru feature which can result in the dock ethernet port using the
same MAC address that is assigned to the internal NIC.  This is done
by calling an ACPI method at \_SB.AMAC() which returns a formatted
string containing the MAC address for the dock to use.

The Linux kernel implementation can be found at
drivers/net/usb/r8152.c:vendor_mac_passthru_addr_read()

This is implemented specifically for Chrome OS as it relies on VPD
to determine the MAC address to supply.

The policy which controls where the dock MAC address comes from is
written into RW_VPD property "dock_passthru":
  "dock_mac" or empty: Use MAC address from RO_VPD value "dock_mac"
  "ethernet_mac0": Use MAC address from RO_VPD value "ethernet_mac0"
  "builtin": existing dock MAC address (return nothing)

The MAC address in VPD is the standard format AA:BB:CC:DD:EE:FF and
it must be converted into the string format expected by the OS which
involves some string manipulation which ACPI is not great at handling.

BUG=b:123925776
TEST=this was tested on a sarien board by setting the VPD keys to
their expected values and observing if the AMAC() method returns the
expected string.

Change-Id: I3335e5d924155431e299844e2aaace62168294e0
Signed-off-by: Duncan Laurie <dlaurie@google.com>
Reviewed-on: https://review.coreboot.org/c/31669
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Lijian Zhao <lijian.zhao@intel.com>

src/vendorcode/google/chromeos/acpi/amac.asl

@@ -0,0 +1,85 @@
+/*
+ * This file is part of the coreboot project.
+ *
+ * Copyright 2019 Google LLC
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; version 2 of
+ * the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+/*
+ * The Realtek r8152 driver in the Linux kernel supports a MAC address
+ * passthru feature which can result in the dock ethernet port using the
+ * same MAC address that is assigned to the internal NIC.  This is done
+ * by calling an ACPI method at \_SB.AMAC() which returns a formatted
+ * string containing the MAC address for the dock to use.
+ *
+ * The Linux kernel implementation can be found at
+ * drivers/net/usb/r8152.c:vendor_mac_passthru_addr_read()
+ *
+ * For Chrome OS, the policy which controls where the dock MAC address
+ * comes from is written into RW_VPD property "dock_passthru":
+ *
+ *   "dock_mac" or empty: Use MAC address from RO_VPD value "dock_mac"
+ *   "ethernet_mac0": Use MAC address from RO_VPD value "ethernet_mac0"
+ *   "builtin": existing dock MAC address (return nothing)
+ */
+
+Scope (\_SB)
+{
+	Method (AMAC, 0, Serialized)
+	{
+		/* Format expected by the Linux kernel r8152 driver */
+		Name (MACA, "_AUXMAC_#XXXXXXXXXXXX#")
+
+		/* Get "dock_passthru" value from RW_VPD */
+		Local0 = \VPD.VPDF ("RW", "dock_passthru")
+
+		Switch (ToString (Local0))
+		{
+			Case ("ethernet_mac0") {
+				Local1 = \VPD.VPDF ("RO", "ethernet_mac0")
+			}
+			Case ("builtin") {
+				Return (Zero)
+			}
+			/* "dock_mac" or policy not found. */
+			Default {
+				Local1 = \VPD.VPDF ("RO", "dock_mac")
+			}
+		}
+		If (!Local1) {
+			Return (Zero)
+		}
+		Printf ("MAC address returned from VPD: %o", Local1)
+
+		/* Verify MAC address format is AA:BB:CC:DD:EE:FF */
+		For (Local3 = 2, Local3 < 17, Local3 += 3) {
+			If (ToString (DerefOf (Local1[Local3])) != ":") {
+				Printf ("Invalid MAC address byte %o", Local3)
+				Return (Zero)
+			}
+		}
+
+		/* Convert MAC address into format specified by MACA */
+		Local2 = ToBuffer (MACA)
+		Local4 = 0 /* First MAC address byte in input buffer */
+		Local5 = 9 /* First MAC address byte in output buffer */
+		For (Local3 = 0, Local3 < 6, Local3++) {
+			Local2[Local5] = DerefOf (Local1[Local4])
+			Local2[Local5 + 1] = DerefOf (Local1[Local4 + 1])
+			Local5 += 2
+			Local4 += 3 /* Skip ":" in address from VPD */
+		}
+
+		Printf ("AMAC = %o", ToString (Local2))
+		Return (ToString (Local2))
+	}
+}