On 06.07.18 18:26, Grant Likely wrote:
Give some rationale behind EBBR so the reader understands what problem the specification is intended to solve.
Signed-off-by: Bill Mills wmills@ti.com [glikely: made it more verbose to make the intent clear] Signed-off-by: Grant Likely grant.likely@arm.com
source/chapter1-about.rst | 94 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 94 insertions(+)
diff --git a/source/chapter1-about.rst b/source/chapter1-about.rst index b667f1b..cb675d9 100644 --- a/source/chapter1-about.rst +++ b/source/chapter1-about.rst @@ -23,6 +23,100 @@ It leverages the prevalent industry standard firmware specification of [UEFI]_. Comments or change requests can be sent to arm.ebbr-discuss@arm.com. +Guiding Principals +==================
+EBBR as a specification defines requirements on platforms and operating systems, +but requirements alone don't provide insight into why the specification is +written the way it is, or what problems it is intended to solve. +Using the assumption that better understanding of the thought process behind +EBBR will result in better implementations, this section is a discussion of the +goals and guiding principle that shaped EBBR.
principles?
+This section should be considered commentary, and not a formal part of the specification.
+EBBR was written as a response to the lack of boot sequence standardization in the embedded system ecosystem. +As embedded systems are becoming more sophisticated and connected, +it is becoming increasingly important for embedded systems to run standard OS +distributions and software stacks, or to have consistent behaviour across a +large deployment of heterogeneous platforms. +However, the lack of consistency between platforms often requires per-platform +customization to get an OS image to boot on multiple platforms.
+A large part of this ecosystem is based on U-Boot and Linux. +Vendors have heavy investments in both projects and are not interested in large +scale changes to their firmware architecture. +The challenge for EBBR is to define a set of boot standards that reduce the +amount of custom engineering required, make it possible for OS distributions to +support embedded platforms, while still preserving the firmware stack product +vendors are comfortable with. +Or in simpler terms, EBBR is designed to solve the embedded boot mess by +migrating existing firmware projects (U-Boot) to a defined standard (UEFI).
+However, EBBR is a specification, not an implementation. +The goal of EBBR is not to mandate U-Boot and Linux. +Rather, it is to mandate interfaces that can be implemented by any firmware or +OS project, while at the same time work with both Tianocore/EDK2 and U-Boot to +ensure that the EBBR requirements are implemented by both projects. +[#EDK2Note]_
+.. [#EDK2Note] Tianocore/EDK2 and U-Boot are highlighted here because at the
- time of writing these are the two most important firmware projects.
You probably want to clarify that they are the most important firmware projects *implementing UEFI*. I'm quite sure that whatever Android does easily outnumbers us ;).
- Tianocore/EDK2 is a full featured UEFI implementation and so should
- automatically be EBBR compliant. U-Boot is the incumbant firmware project
- for embedded platforms and has added basic UEFI compliance.
This document will love for a while. Maybe better document it as trajectory:
... and has steadily been adding UEFI compliance since 2016.
+The following guiding principals of the EBBR specification and its
principles again, but I guess you'll just search&replace.
+process:
+- Be agnostic about ACPI and Devicetree.
- EBBR explicitly does not require a specific system description language.
- Both Devicetree and ACPI are supported.
- While ACPI provides more standardization, Devicetree is preferred in may embedded
many
- platforms for its flexibility.
- The Linux kernel supports both equally well, and so EBBR doesn't require one
- over the other.
- However, it does require the system description to be provided by the
- platform, and that it conform to the relevant ACPI or DT specifications.
... and adhere to strict compatbility rules.
Alex