Booting the Linux/ppc kernel without Open Firmware
--------------------------------------------------
(c) 2005 Benjamin Herrenschmidt <benh at kernel.crashing.org>,
IBM Corp.
(c) 2005 Becky Bruce <becky.bruce at freescale.com>,
Freescale Semiconductor, FSL SOC and 32-bit additions
(c) 2006 MontaVista Software, Inc.
Flash chip node definition
Table of Contents
=================
I - Introduction
1) Entry point for arch/powerpc
2) Entry point for arch/x86
II - The DT block format
1) Header
2) Device tree generalities
3) Device tree "structure" block
4) Device tree "strings" block
III - Required content of the device tree
1) Note about cells and address representation
2) Note about "compatible" properties
3) Note about "name" properties
4) Note about node and property names and character set
5) Required nodes and properties
a) The root node
b) The /cpus node
c) The /cpus/* nodes
d) the /memory node(s)
e) The /chosen node
f) the /soc<SOCname> node
IV - "dtc", the device tree compiler
V - Recommendations for a bootloader
VI - System-on-a-chip devices and nodes
1) Defining child nodes of an SOC
2) Representing devices without a current OF specification
VII - Specifying interrupt information for devices
1) interrupts property
2) interrupt-parent property
3) OpenPIC Interrupt Controllers
4) ISA Interrupt Controllers
VIII - Specifying device power management information (sleep property)
Appendix A - Sample SOC node for MPC8540
Revision Information
====================
May 18, 2005: Rev 0.1 - Initial draft, no chapter III yet.
May 19, 2005: Rev 0.2 - Add chapter III and bits & pieces here or
clarifies the fact that a lot of things are
optional, the kernel only requires a very
small device tree, though it is encouraged
to provide an as complete one as possible.
May 24, 2005: Rev 0.3 - Precise that DT block has to be in RAM
- Misc fixes
- Define version 3 and new format version 16
for the DT block (version 16 needs kernel
patches, will be fwd separately).
String block now has a size, and full path
is replaced by unit name for more
compactness.
linux,phandle is made optional, only nodes
that are referenced by other nodes need it.
"name" property is now automatically
deduced from the unit name
June 1, 2005: Rev 0.4 - Correct confusion between OF_DT_END and
OF_DT_END_NODE in structure definition.
- Change version 16 format to always align
property data to 4 bytes. Since tokens are
already aligned, that means no specific
required alignment between property size
and property data. The old style variable
alignment would make it impossible to do
"simple" insertion of properties using
memmove (thanks Milton for
noticing). Updated kernel patch as well
- Correct a few more alignment constraints
- Add a chapter about the device-tree
compiler and the textural representation of
the tree that can be "compiled" by dtc.
November 21, 2005: Rev 0.5
- Additions/generalizations for 32-bit
- Changed to reflect the new arch/powerpc
structure
- Added chapter VI
ToDo:
- Add some definitions of interrupt tree (simple/complex)
- Add some definitions for PCI host bridges
- Add some common address format examples
- Add definitions for standard properties and "compatible"
names for cells that are not already defined by the existing
OF spec.
- Compare FSL SOC use of PCI to standard and make sure no new
node definition required.
- Add more information about node definitions for SOC devices
that currently have no standard, like the FSL CPM.
I - Introduction
================
During the development of the Linux/ppc64 kernel, and more
specifically, the addition of new platform types outside of the old
IBM pSeries/iSeries pair, it was decided to enforce some strict rules
regarding the kernel entry and bootloader <-> kernel interfaces, in
order to avoid the degeneration that had become the ppc32 kernel entry
point and the way a new platform should be added to the kernel. The
legacy iSeries platform breaks those rules as it predates this scheme,
but no new board support will be accepted in the main tree that
doesn't follow them properly. In addition, since the advent of the
arch/powerpc merged architecture for ppc32 and ppc64, new 32-bit
platforms and 32-bit platforms which move into arch/powerpc will be
required to use these rules as well.
The main requirement that will be defined in more detail below is
the presence of a device-tree whose format is defined after Open
Firmware specification. However, in order to make life easier
to embedded board vendors, the kernel doesn't require the device-tree
to represent every device in the system and only requires some nodes
and properties to be present. This will be described in detail in
section III, but, for example, the kernel does not require you to
create a node for every PCI device in the system. It is a requirement
to have a node for PCI host bridges in order to provide interrupt
routing information and memory/IO ranges, among others. It is also
recommended to define nodes for on chip devices and other buses that
don't specifically fit in an existing OF specification. This creates a
great flexibility in the way the kernel can then probe those and match
drivers to device, without having to hard code all sorts of tables. It
also makes it more flexible for board vendors to do minor hardware
upgrades without significantly impacting the kernel code or cluttering
it with special cases.
1) Entry point for arch/powerpc
-------------------------------
There is one single entry point to the kernel, at the start
of the kernel image. That entry point supports two calling
conventions:
a) Boot from Open Firmware. If your firmware is compatible
with Open Firmware (IEEE 1275) or provides an OF compatible
client interface API (support for "interpret" callback of
forth words isn't required), you can enter the kernel with:
r5 : OF callback pointer as defined by IEEE 1275
bindings to powerpc. Only the 32-bit client interface
is currently supported
r3, r4 : address & length of an initrd if any or 0
The MMU is either on or off; the kernel will run the
trampoline located in arch/powerpc/kernel/prom_init.c to
extract the device-tree and other information from open
firmware and build a flattened device-tree as described
in b). prom_init() will then re-enter the kernel using
the second method. This trampoline code runs in the
context of the firmware, which is supposed to handle all
exceptions during that time.
b) Direct entry with a flattened device-tree block. This entry
point is c