[RFC PATCH v1 0/3] device property: Support MAC address in VPD

[Brian Norris]

Hi all,

Preface: I'm sure there are at least a few minor issues with this
patchset as-is. But I'd appreciate ("RFC") if I can get general feedback
on the approach here; perhaps there are alternatives, or perhaps I've
missed similar proposals in the past. (My problems don't feel all that
unique.)

---

Today, we have generic support for 'mac-address' and 'local-mac-address'
properties in both Device Tree nodes and in generic Device Properties,
such that network device drivers can pick up a hardware address from
there, in cases where the MAC address isn't baked into the network card.
This method of MAC address retrieval presumes that either:
(a) there's a unique device tree (or similar) stored on a given device
    or
(b) some other entity (e.g., boot firmware) will modify device nodes
    runtime to place that MAC address into the appropriate device
    properties.

Option (a) is not feasbile for many systems.

Option (b) can work, but there are some reasons why one might not want
to do that:
 (1) This requires that system firmware understand the device tree
     structure, sometimes to the point of memorizing path names (e.g.,
     /soc/wifi@xxxxxxxx). At least for Device Tree, these path names are
     not necessarily an ABI, and so this introduces unneeded fragility.
 (2) Other than this device-tree shim requirement, system firmware may
     have no reason to understand anything about network devices.

So instead, I'm looking for a way to have a device node describe where
to find its MAC address, rather than having the device node contain the
MAC address directly. Then system firmware doesn't have to manage
anything.

In particular, I add support for the Google Vital Product Data (VPD)
format, used within the Coreboot project. The format is described here:

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.

We already have a VPD driver that parses this table and presents it to
user space. This series extends that driver to allow in-kernel lookups
of MAC address entries.

Thanks,
Brian


Brian Norris (3):
  dt-bindings: net: Add 'mac-address-lookup' property
  device property: Support complex MAC address lookup
  firmware: vpd: add MAC address parser

 .../devicetree/bindings/net/ethernet.txt      | 12 +++
 drivers/base/property.c                       | 83 ++++++++++++++++++-
 drivers/firmware/google/vpd.c                 | 67 +++++++++++++++
 include/linux/property.h                      | 23 +++++
 4 files changed, 183 insertions(+), 2 deletions(-)

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2.18.0.865.gffc8e1a3cd6-goog