[PATCH v3 2/3] schemas: Add firmware node schema

Simon Glass sjg at chromium.org
Mon Aug 21 20:01:16 CEST 2023

Add a motivation and purpose for this new proposed node.

Signed-off-by: Simon Glass <sjg at chromium.org>

(no changes since v1)

 dtschema/schemas/firmware.yaml | 83 ++++++++++++++++++++++++++++++++++
 1 file changed, 83 insertions(+)
 create mode 100644 dtschema/schemas/firmware.yaml

diff --git a/dtschema/schemas/firmware.yaml b/dtschema/schemas/firmware.yaml
new file mode 100644
index 0000000..4439a70
--- /dev/null
+++ b/dtschema/schemas/firmware.yaml
@@ -0,0 +1,83 @@
+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-clause
+# Copyright 2023 Google LLC
+%YAML 1.2
+$id: http://devicetree.org/schemas/firmware.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+title: /firmware Node
+  - Simon Glass <sjg at chromium.org>
+description: |
+  The '/firmware' node does not represent a real device, but serves as a place
+  for recording information about the main firmware used on the device, such as
+  a map of its contents. This is used by the Operating System (OS), user space
+  programs and possibly other firmware components. Data in the '/firmware' node
+  does not itself represent the hardware.
+  Properties in this node should be common to (and used by) at least two
+  firmware projects, such as U-Boot and TF-A. Project-specific subnodes can be
+  used for properties which are specific to a single project.
+  Purpose of '/firmware' node
+  ---------------------------
+  Firmware has traditionally been fairly opaque to the OS, with the OS taking
+  no interest in its contents, version, layout or how it might be updated. This
+  is less than ideal, since firmware is an important part of the system and
+  visibility into its operation is every bit as important as visbility into the
+  OS and user-space programs within the system.
+  The traditional approach has been to let firmware deal with firmware, and the
+  OS deal with everything else. Updating firmware has been handled by firmware.
+  For example, the UEFI spec defines a way for the OS to post a 'capsule' which
+  is discovered next time the system boots, permitting firmware updates. But
+  firmware updates in firmware are highly problematic. They require a reboot
+  and a sometimes-lengthy wait with a strange-looking interface unfamiliar
+  to most users. It seems better to make the update as transparent as possible
+  to the user. As an example of that, ChromeOS has full knowledge of the
+  firmware version and layout, updates it in the background from user space and
+  instantly selects the new firmware when the user reboots or logs out.
+  A common objection to considering the system holistically is that some parts
+  of the system are inaccessible to the OS, such as a secure enclave. However
+  this does not preclude providing visibility into what is present in that
+  enclave. Firmware-version information is still useful. Firmware updates are
+  still needed and can still be initiated from user space.
+  Another objection is that firmware should provide an interface to the OS,
+  while keeping its structure private. This thinking is largely driven by
+  extrapolating from how firmware has been handled in the 'BIOS' days.
+  It should be considered a degenerate case rather than the norm. As complexity
+  increases, it creates an artificial boundary between two pieces of the whole.
+  Mechanisms then need to be invented to cross this unnecessary chasm. An
+  example of this is Intel's Dynamic Platform and Thermal Framework (DPTF),
+  which consists of user-space, OS and firmware components all working towards
+  a shared goal. We need a standard description of these cross-system pieces.
+  In order to 'teach the OS about firmware', we need a place to put this
+  information. That is the purpose of this node.
+  In an Open Source world the entire model of firmware needs to adjust to be
+  more open, more visible and managed just like any other part of the system.
+  The major goal is to standardise how firmware is presented to the OS and user
+  space, so that common utilities can be used to manage the entire system,
+  including the firmware. For example, fwupd can look in this node for
+  information on how to update the firmware, similar to how VBE works. [1]
+  It is likely that other purposes will come to light over time.
+  [1] https://github.com/fwupd/fwupd/tree/main/plugins/vbe
+  $nodename:
+    const: firmware
+  "#address-cells": true
+  "#size-cells": true
+  type: object

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