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From:   Brian Norris <computersforpeace@gmail.com>
To:     Rob Herring <robh+dt@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>
Cc:     Andrew Lunn <andrew@lunn.ch>,
        Florian Fainelli <f.fainelli@gmail.com>,
        Dmitry Torokhov <dmitry.torokhov@gmail.com>,
        Guenter Roeck <linux@roeck-us.net>, netdev@vger.kernel.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        Julius Werner <jwerner@chromium.org>,
        Stephen Boyd <swboyd@chromium.org>,
        Brian Norris <briannorris@chromium.org>
Subject: [RFC PATCH v1 1/3] dt-bindings: net: Add 'mac-address-lookup' property
Date:   Tue, 14 Aug 2018 15:37:56 -0700
Message-Id: <20180814223758.117433-2-briannorris@chromium.org>
In-Reply-To: <20180814223758.117433-1-briannorris@chromium.org>
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Some firmwares present data tables that can be parsed to retrieve
device-specific details, like MAC addresses. While in some cases, one
could teach the firmware to understand the device tree format and insert
a 'mac-address'/'local-mac-address' property into the FDT on its own,
this method can be brittle (e.g., involving memorizing expected FDT
structure), and it's not strictly necessary -- especially when parsers
for such firmware formats are already needed in the OS for other
reasons.

One such format: the Vital Product Data (VPD) [1] used by Coreboot. It
supports a table of key/value pairs, and some systems keep MAC addresses
there in a well-known format. Allow a device tree to specify
  (1) that the MAC address for a given device is stored in the VPD table
      and
  (2) what key should be used to retrieve the MAC address for said
      device (e.g., "ethernet_mac0" or "wifi_mac1").

[1] Ref:
https://chromium.googlesource.com/chromiumos/platform/vpd/+/master/README.md
TL;DR: VPD consists of a TLV-like table, with key/value pairs of
strings. This is often stored persistently on the boot flash and
presented via in-memory Coreboot tables, for the operating system to
read.

Signed-off-by: Brian Norris <briannorris@chromium.org>
---
 Documentation/devicetree/bindings/net/ethernet.txt | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/Documentation/devicetree/bindings/net/ethernet.txt b/Documentation/devicetree/bindings/net/ethernet.txt
index cfc376bc977a..d3fd1da18bf4 100644
--- a/Documentation/devicetree/bindings/net/ethernet.txt
+++ b/Documentation/devicetree/bindings/net/ethernet.txt
@@ -4,6 +4,18 @@ NOTE: All 'phy*' properties documented below are Ethernet specific. For the
 generic PHY 'phys' property, see
 Documentation/devicetree/bindings/phy/phy-bindings.txt.
 
+- mac-address-lookup: string, indicating a method by which a MAC address may be
+  discovered for this device. Methods may be parameterized by some value, such
+  that the method can determine the device's MAC address using that parameter.
+  For example, a firmware might store MAC addresses in a table, keyed by some
+  predetermined string, and baked in read-only flash. A lookup method "foo"
+  with a parameter "bar" should be written "foo:bar".
+  Supported values for method:
+    "google-vpd" - Google's Vital Product Data (VPD), as used in the Coreboot
+      project. Documentation for VPD can be found at:
+        https://chromium.googlesource.com/chromiumos/platform/vpd/+/master/README.md
+  Example:
+    mac-address-lookup = "google-vpd:ethernet_mac0"
 - local-mac-address: array of 6 bytes, specifies the MAC address that was
   assigned to the network device;
 - mac-address: array of 6 bytes, specifies the MAC address that was last used by
-- 
2.18.0.865.gffc8e1a3cd6-goog