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Message-ID: <1b7f5ee0-b955-698e-2fe8-be6e775e0f49@gmail.com>
Date: Thu, 5 Mar 2020 16:48:23 -0600
From: Frank Rowand <frowand.list@...il.com>
To: Rob Herring <robh@...nel.org>, devicetree@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
Mauro Carvalho Chehab <mchehab@...nel.org>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Geert Uytterhoeven <geert+renesas@...der.be>,
Michael Ellerman <mpe@...erman.id.au>,
linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] dt: Remove booting-without-of.txt
On 3/4/20 12:45 PM, Rob Herring wrote:
> Well, not quite removed yet... Mauro is looking at moving this to ReST,
> but I think it would be better to trim or remove it.
>
> boot-without-of.txt is an ancient document that first outlined
> Flattened DeviceTree. The DT world has evolved a lot in the 15 years
> since and boot-without-of.txt is pretty stale. The name of the document
> itself is confusing if you don't understand the evolution from real
> 'OpenFirmware'. Much of what booting-without-of.txt contains is now in
> the DT specification (which evolved out of the ePAPR).
>
> This is a first pass of removing everything that has a DT spec
> equivalent or is no longer standard practice (e.g. soc<SoCName> for SoC
> nodes) in order to see what's left. This is what I have:
>
> TODO
> - Move boot interface details to arch specific docs
> - Document 'serial-number' property in DT spec
> - Document the 'hotpluggable' memory property in DT spec
> - Document the 'sleep' property (PPC only)
> - Document the 'dma-coherent' property in DT spec
> - Need the history of node names and 'name' property?
> - Need how addresses work?
Looks good. Since this is a first pass, I'm expecting that polishing
(things like updating section numbers) would happen in subsequent
patches after more of the content changes are done, so no need
to do so in this patch.
Reviewed-by: Frank Rowand <frank.rowand@...y.com>
-Frank
>
> Cc: Frank Rowand <frowand.list@...il.com>
> Cc: Mauro Carvalho Chehab <mchehab@...nel.org>
> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Cc: Geert Uytterhoeven <geert+renesas@...der.be>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Cc: linuxppc-dev@...ts.ozlabs.org
> Signed-off-by: Rob Herring <robh@...nel.org>
> ---
> .../devicetree/booting-without-of.txt | 1027 +----------------
> 1 file changed, 1 insertion(+), 1026 deletions(-)
>
> diff --git a/Documentation/devicetree/booting-without-of.txt b/Documentation/devicetree/booting-without-of.txt
> index 4660ccee35a3..97beee828ba4 100644
> --- a/Documentation/devicetree/booting-without-of.txt
> +++ b/Documentation/devicetree/booting-without-of.txt
> @@ -19,44 +19,17 @@ Table of Contents
> 5) Entry point for arch/sh
>
> 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)
>
> IX - Specifying dma bus information
>
> - Appendix A - Sample SOC node for MPC8540
> -
>
> Revision Information
> ====================
> @@ -105,19 +78,6 @@ Revision Information
> - 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
> ================
>
> @@ -333,196 +293,17 @@ II - The DT block format
> ========================
>
>
> -This chapter defines the actual format of the flattened device-tree
> -passed to the kernel. The actual content of it and kernel requirements
> -are described later. You can find example of code manipulating that
> -format in various places, including arch/powerpc/kernel/prom_init.c
> -which will generate a flattened device-tree from the Open Firmware
> -representation, or the fs2dt utility which is part of the kexec tools
> -which will generate one from a filesystem representation. It is
> -expected that a bootloader like uboot provides a bit more support,
> -that will be discussed later as well.
> -
> Note: The block has to be in main memory. It has to be accessible in
> both real mode and virtual mode with no mapping other than main
> memory. If you are writing a simple flash bootloader, it should copy
> the block to RAM before passing it to the kernel.
>
>
> -1) Header
> ----------
> -
> - The kernel is passed the physical address pointing to an area of memory
> - that is roughly described in include/linux/of_fdt.h by the structure
> - boot_param_header:
> -
> -struct boot_param_header {
> - u32 magic; /* magic word OF_DT_HEADER */
> - u32 totalsize; /* total size of DT block */
> - u32 off_dt_struct; /* offset to structure */
> - u32 off_dt_strings; /* offset to strings */
> - u32 off_mem_rsvmap; /* offset to memory reserve map
> - */
> - u32 version; /* format version */
> - u32 last_comp_version; /* last compatible version */
> -
> - /* version 2 fields below */
> - u32 boot_cpuid_phys; /* Which physical CPU id we're
> - booting on */
> - /* version 3 fields below */
> - u32 size_dt_strings; /* size of the strings block */
> -
> - /* version 17 fields below */
> - u32 size_dt_struct; /* size of the DT structure block */
> -};
> -
> - Along with the constants:
> -
> -/* Definitions used by the flattened device tree */
> -#define OF_DT_HEADER 0xd00dfeed /* 4: version,
> - 4: total size */
> -#define OF_DT_BEGIN_NODE 0x1 /* Start node: full name
> - */
> -#define OF_DT_END_NODE 0x2 /* End node */
> -#define OF_DT_PROP 0x3 /* Property: name off,
> - size, content */
> -#define OF_DT_END 0x9
> -
> - All values in this header are in big endian format, the various
> - fields in this header are defined more precisely below. All
> - "offset" values are in bytes from the start of the header; that is
> - from the physical base address of the device tree block.
> -
> - - magic
> -
> - This is a magic value that "marks" the beginning of the
> - device-tree block header. It contains the value 0xd00dfeed and is
> - defined by the constant OF_DT_HEADER
> -
> - - totalsize
> -
> - This is the total size of the DT block including the header. The
> - "DT" block should enclose all data structures defined in this
> - chapter (who are pointed to by offsets in this header). That is,
> - the device-tree structure, strings, and the memory reserve map.
> -
> - - off_dt_struct
> -
> - This is an offset from the beginning of the header to the start
> - of the "structure" part the device tree. (see 2) device tree)
> -
> - - off_dt_strings
> -
> - This is an offset from the beginning of the header to the start
> - of the "strings" part of the device-tree
> -
> - - off_mem_rsvmap
> -
> - This is an offset from the beginning of the header to the start
> - of the reserved memory map. This map is a list of pairs of 64-
> - bit integers. Each pair is a physical address and a size. The
> - list is terminated by an entry of size 0. This map provides the
> - kernel with a list of physical memory areas that are "reserved"
> - and thus not to be used for memory allocations, especially during
> - early initialization. The kernel needs to allocate memory during
> - boot for things like un-flattening the device-tree, allocating an
> - MMU hash table, etc... Those allocations must be done in such a
> - way to avoid overriding critical things like, on Open Firmware
> - capable machines, the RTAS instance, or on some pSeries, the TCE
> - tables used for the iommu. Typically, the reserve map should
> - contain _at least_ this DT block itself (header,total_size). If
> - you are passing an initrd to the kernel, you should reserve it as
> - well. You do not need to reserve the kernel image itself. The map
> - should be 64-bit aligned.
> -
> - - version
> -
> - This is the version of this structure. Version 1 stops
> - here. Version 2 adds an additional field boot_cpuid_phys.
> - Version 3 adds the size of the strings block, allowing the kernel
> - to reallocate it easily at boot and free up the unused flattened
> - structure after expansion. Version 16 introduces a new more
> - "compact" format for the tree itself that is however not backward
> - compatible. Version 17 adds an additional field, size_dt_struct,
> - allowing it to be reallocated or moved more easily (this is
> - particularly useful for bootloaders which need to make
> - adjustments to a device tree based on probed information). You
> - should always generate a structure of the highest version defined
> - at the time of your implementation. Currently that is version 17,
> - unless you explicitly aim at being backward compatible.
> -
> - - last_comp_version
> -
> - Last compatible version. This indicates down to what version of
> - the DT block you are backward compatible. For example, version 2
> - is backward compatible with version 1 (that is, a kernel build
> - for version 1 will be able to boot with a version 2 format). You
> - should put a 1 in this field if you generate a device tree of
> - version 1 to 3, or 16 if you generate a tree of version 16 or 17
> - using the new unit name format.
> -
> - - boot_cpuid_phys
> -
> - This field only exist on version 2 headers. It indicate which
> - physical CPU ID is calling the kernel entry point. This is used,
> - among others, by kexec. If you are on an SMP system, this value
> - should match the content of the "reg" property of the CPU node in
> - the device-tree corresponding to the CPU calling the kernel entry
> - point (see further chapters for more information on the required
> - device-tree contents)
> -
> - - size_dt_strings
> -
> - This field only exists on version 3 and later headers. It
> - gives the size of the "strings" section of the device tree (which
> - starts at the offset given by off_dt_strings).
> -
> - - size_dt_struct
> -
> - This field only exists on version 17 and later headers. It gives
> - the size of the "structure" section of the device tree (which
> - starts at the offset given by off_dt_struct).
> -
> - So the typical layout of a DT block (though the various parts don't
> - need to be in that order) looks like this (addresses go from top to
> - bottom):
> -
> -
> - ------------------------------
> - base -> | struct boot_param_header |
> - ------------------------------
> - | (alignment gap) (*) |
> - ------------------------------
> - | memory reserve map |
> - ------------------------------
> - | (alignment gap) |
> - ------------------------------
> - | |
> - | device-tree structure |
> - | |
> - ------------------------------
> - | (alignment gap) |
> - ------------------------------
> - | |
> - | device-tree strings |
> - | |
> - -----> ------------------------------
> - |
> - |
> - --- (base + totalsize)
> -
> - (*) The alignment gaps are not necessarily present; their presence
> - and size are dependent on the various alignment requirements of
> - the individual data blocks.
>
>
> 2) Device tree generalities
> ---------------------------
>
> -This device-tree itself is separated in two different blocks, a
> -structure block and a strings block. Both need to be aligned to a 4
> -byte boundary.
> -
> First, let's quickly describe the device-tree concept before detailing
> the storage format. This chapter does _not_ describe the detail of the
> required types of nodes & properties for the kernel, this is done
> @@ -574,128 +355,6 @@ is) is also required to have a "compatible" property indicating the
> specific hardware and an optional list of devices it is fully
> backwards compatible with.
>
> -Finally, every node that can be referenced from a property in another
> -node is required to have either a "phandle" or a "linux,phandle"
> -property. Real Open Firmware implementations provide a unique
> -"phandle" value for every node that the "prom_init()" trampoline code
> -turns into "linux,phandle" properties. However, this is made optional
> -if the flattened device tree is used directly. An example of a node
> -referencing another node via "phandle" is when laying out the
> -interrupt tree which will be described in a further version of this
> -document.
> -
> -The "phandle" property is a 32-bit value that uniquely
> -identifies a node. You are free to use whatever values or system of
> -values, internal pointers, or whatever to generate these, the only
> -requirement is that every node for which you provide that property has
> -a unique value for it.
> -
> -Here is an example of a simple device-tree. In this example, an "o"
> -designates a node followed by the node unit name. Properties are
> -presented with their name followed by their content. "content"
> -represents an ASCII string (zero terminated) value, while <content>
> -represents a 32-bit value, specified in decimal or hexadecimal (the
> -latter prefixed 0x). The various nodes in this example will be
> -discussed in a later chapter. At this point, it is only meant to give
> -you a idea of what a device-tree looks like. I have purposefully kept
> -the "name" and "linux,phandle" properties which aren't necessary in
> -order to give you a better idea of what the tree looks like in
> -practice.
> -
> - / o device-tree
> - |- name = "device-tree"
> - |- model = "MyBoardName"
> - |- compatible = "MyBoardFamilyName"
> - |- #address-cells = <2>
> - |- #size-cells = <2>
> - |- linux,phandle = <0>
> - |
> - o cpus
> - | | - name = "cpus"
> - | | - linux,phandle = <1>
> - | | - #address-cells = <1>
> - | | - #size-cells = <0>
> - | |
> - | o PowerPC,970@0
> - | |- name = "PowerPC,970"
> - | |- device_type = "cpu"
> - | |- reg = <0>
> - | |- clock-frequency = <0x5f5e1000>
> - | |- 64-bit
> - | |- linux,phandle = <2>
> - |
> - o memory@0
> - | |- name = "memory"
> - | |- device_type = "memory"
> - | |- reg = <0x00000000 0x00000000 0x00000000 0x20000000>
> - | |- linux,phandle = <3>
> - |
> - o chosen
> - |- name = "chosen"
> - |- bootargs = "root=/dev/sda2"
> - |- linux,phandle = <4>
> -
> -This tree is almost a minimal tree. It pretty much contains the
> -minimal set of required nodes and properties to boot a linux kernel;
> -that is, some basic model information at the root, the CPUs, and the
> -physical memory layout. It also includes misc information passed
> -through /chosen, like in this example, the platform type (mandatory)
> -and the kernel command line arguments (optional).
> -
> -The /cpus/PowerPC,970@...4-bit property is an example of a
> -property without a value. All other properties have a value. The
> -significance of the #address-cells and #size-cells properties will be
> -explained in chapter IV which defines precisely the required nodes and
> -properties and their content.
> -
> -
> -3) Device tree "structure" block
> -
> -The structure of the device tree is a linearized tree structure. The
> -"OF_DT_BEGIN_NODE" token starts a new node, and the "OF_DT_END_NODE"
> -ends that node definition. Child nodes are simply defined before
> -"OF_DT_END_NODE" (that is nodes within the node). A 'token' is a 32
> -bit value. The tree has to be "finished" with a OF_DT_END token
> -
> -Here's the basic structure of a single node:
> -
> - * token OF_DT_BEGIN_NODE (that is 0x00000001)
> - * for version 1 to 3, this is the node full path as a zero
> - terminated string, starting with "/". For version 16 and later,
> - this is the node unit name only (or an empty string for the
> - root node)
> - * [align gap to next 4 bytes boundary]
> - * for each property:
> - * token OF_DT_PROP (that is 0x00000003)
> - * 32-bit value of property value size in bytes (or 0 if no
> - value)
> - * 32-bit value of offset in string block of property name
> - * property value data if any
> - * [align gap to next 4 bytes boundary]
> - * [child nodes if any]
> - * token OF_DT_END_NODE (that is 0x00000002)
> -
> -So the node content can be summarized as a start token, a full path,
> -a list of properties, a list of child nodes, and an end token. Every
> -child node is a full node structure itself as defined above.
> -
> -NOTE: The above definition requires that all property definitions for
> -a particular node MUST precede any subnode definitions for that node.
> -Although the structure would not be ambiguous if properties and
> -subnodes were intermingled, the kernel parser requires that the
> -properties come first (up until at least 2.6.22). Any tools
> -manipulating a flattened tree must take care to preserve this
> -constraint.
> -
> -4) Device tree "strings" block
> -
> -In order to save space, property names, which are generally redundant,
> -are stored separately in the "strings" block. This block is simply the
> -whole bunch of zero terminated strings for all property names
> -concatenated together. The device-tree property definitions in the
> -structure block will contain offset values from the beginning of the
> -strings block.
> -
>
> III - Required content of the device tree
> =========================================
> @@ -792,568 +451,14 @@ registers are visible on the parent bus using an identity mapping
> translation. In other words, the parent bus address space is the same
> as the child bus address space.
>
> -2) Note about "compatible" properties
> --------------------------------------
> -
> -These properties are optional, but recommended in devices and the root
> -node. The format of a "compatible" property is a list of concatenated
> -zero terminated strings. They allow a device to express its
> -compatibility with a family of similar devices, in some cases,
> -allowing a single driver to match against several devices regardless
> -of their actual names.
> -
> -3) Note about "name" properties
> --------------------------------
> -
> -While earlier users of Open Firmware like OldWorld macintoshes tended
> -to use the actual device name for the "name" property, it's nowadays
> -considered a good practice to use a name that is closer to the device
> -class (often equal to device_type). For example, nowadays, Ethernet
> -controllers are named "ethernet", an additional "model" property
> -defining precisely the chip type/model, and "compatible" property
> -defining the family in case a single driver can driver more than one
> -of these chips. However, the kernel doesn't generally put any
> -restriction on the "name" property; it is simply considered good
> -practice to follow the standard and its evolutions as closely as
> -possible.
> -
> -Note also that the new format version 16 makes the "name" property
> -optional. If it's absent for a node, then the node's unit name is then
> -used to reconstruct the name. That is, the part of the unit name
> -before the "@" sign is used (or the entire unit name if no "@" sign
> -is present).
> -
> -4) Note about node and property names and character set
> --------------------------------------------------------
> -
> -While Open Firmware provides more flexible usage of 8859-1, this
> -specification enforces more strict rules. Nodes and properties should
> -be comprised only of ASCII characters 'a' to 'z', '0' to
> -'9', ',', '.', '_', '+', '#', '?', and '-'. Node names additionally
> -allow uppercase characters 'A' to 'Z' (property names should be
> -lowercase. The fact that vendors like Apple don't respect this rule is
> -irrelevant here). Additionally, node and property names should always
> -begin with a character in the range 'a' to 'z' (or 'A' to 'Z' for node
> -names).
> -
> -The maximum number of characters for both nodes and property names
> -is 31. In the case of node names, this is only the leftmost part of
> -a unit name (the pure "name" property), it doesn't include the unit
> -address which can extend beyond that limit.
> -
>
> 5) Required nodes and properties
> --------------------------------
> - These are all that are currently required. However, it is strongly
> - recommended that you expose PCI host bridges as documented in the
> - PCI binding to Open Firmware, and your interrupt tree as documented
> - in OF interrupt tree specification.
> -
> - a) The root node
> -
> - The root node requires some properties to be present:
> -
> - - model : this is your board name/model
> - - #address-cells : address representation for "root" devices
> - - #size-cells: the size representation for "root" devices
> - - compatible : the board "family" generally finds its way here,
> - for example, if you have 2 board models with a similar layout,
> - that typically get driven by the same platform code in the
> - kernel, you would specify the exact board model in the
> - compatible property followed by an entry that represents the SoC
> - model.
> -
> - The root node is also generally where you add additional properties
> - specific to your board like the serial number if any, that sort of
> - thing. It is recommended that if you add any "custom" property whose
> - name may clash with standard defined ones, you prefix them with your
> - vendor name and a comma.
>
> Additional properties for the root node:
>
> - serial-number : a string representing the device's serial number
>
> - b) The /cpus node
> -
> - This node is the parent of all individual CPU nodes. It doesn't
> - have any specific requirements, though it's generally good practice
> - to have at least:
> -
> - #address-cells = <00000001>
> - #size-cells = <00000000>
> -
> - This defines that the "address" for a CPU is a single cell, and has
> - no meaningful size. This is not necessary but the kernel will assume
> - that format when reading the "reg" properties of a CPU node, see
> - below
> -
> - c) The /cpus/* nodes
> -
> - So under /cpus, you are supposed to create a node for every CPU on
> - the machine. There is no specific restriction on the name of the
> - CPU, though it's common to call it <architecture>,<core>. For
> - example, Apple uses PowerPC,G5 while IBM uses PowerPC,970FX.
> - However, the Generic Names convention suggests that it would be
> - better to simply use 'cpu' for each cpu node and use the compatible
> - property to identify the specific cpu core.
> -
> - Required properties:
> -
> - - device_type : has to be "cpu"
> - - reg : This is the physical CPU number, it's a single 32-bit cell
> - and is also used as-is as the unit number for constructing the
> - unit name in the full path. For example, with 2 CPUs, you would
> - have the full path:
> - /cpus/PowerPC,970FX@0
> - /cpus/PowerPC,970FX@1
> - (unit addresses do not require leading zeroes)
> - - d-cache-block-size : one cell, L1 data cache block size in bytes (*)
> - - i-cache-block-size : one cell, L1 instruction cache block size in
> - bytes
> - - d-cache-size : one cell, size of L1 data cache in bytes
> - - i-cache-size : one cell, size of L1 instruction cache in bytes
> -
> -(*) The cache "block" size is the size on which the cache management
> -instructions operate. Historically, this document used the cache
> -"line" size here which is incorrect. The kernel will prefer the cache
> -block size and will fallback to cache line size for backward
> -compatibility.
> -
> - Recommended properties:
> -
> - - timebase-frequency : a cell indicating the frequency of the
> - timebase in Hz. This is not directly used by the generic code,
> - but you are welcome to copy/paste the pSeries code for setting
> - the kernel timebase/decrementer calibration based on this
> - value.
> - - clock-frequency : a cell indicating the CPU core clock frequency
> - in Hz. A new property will be defined for 64-bit values, but if
> - your frequency is < 4Ghz, one cell is enough. Here as well as
> - for the above, the common code doesn't use that property, but
> - you are welcome to re-use the pSeries or Maple one. A future
> - kernel version might provide a common function for this.
> - - d-cache-line-size : one cell, L1 data cache line size in bytes
> - if different from the block size
> - - i-cache-line-size : one cell, L1 instruction cache line size in
> - bytes if different from the block size
> -
> - You are welcome to add any property you find relevant to your board,
> - like some information about the mechanism used to soft-reset the
> - CPUs. For example, Apple puts the GPIO number for CPU soft reset
> - lines in there as a "soft-reset" property since they start secondary
> - CPUs by soft-resetting them.
> -
> -
> - d) the /memory node(s)
> -
> - To define the physical memory layout of your board, you should
> - create one or more memory node(s). You can either create a single
> - node with all memory ranges in its reg property, or you can create
> - several nodes, as you wish. The unit address (@ part) used for the
> - full path is the address of the first range of memory defined by a
> - given node. If you use a single memory node, this will typically be
> - @0.
> -
> - Required properties:
> -
> - - device_type : has to be "memory"
> - - reg : This property contains all the physical memory ranges of
> - your board. It's a list of addresses/sizes concatenated
> - together, with the number of cells of each defined by the
> - #address-cells and #size-cells of the root node. For example,
> - with both of these properties being 2 like in the example given
> - earlier, a 970 based machine with 6Gb of RAM could typically
> - have a "reg" property here that looks like:
> -
> - 00000000 00000000 00000000 80000000
> - 00000001 00000000 00000001 00000000
> -
> - That is a range starting at 0 of 0x80000000 bytes and a range
> - starting at 0x100000000 and of 0x100000000 bytes. You can see
> - that there is no memory covering the IO hole between 2Gb and
> - 4Gb. Some vendors prefer splitting those ranges into smaller
> - segments, but the kernel doesn't care.
> -
> - Additional properties:
> -
> - - hotpluggable : The presence of this property provides an explicit
> - hint to the operating system that this memory may potentially be
> - removed later. The kernel can take this into consideration when
> - doing nonmovable allocations and when laying out memory zones.
> -
> - e) The /chosen node
> -
> - This node is a bit "special". Normally, that's where Open Firmware
> - puts some variable environment information, like the arguments, or
> - the default input/output devices.
> -
> - This specification makes a few of these mandatory, but also defines
> - some linux-specific properties that would be normally constructed by
> - the prom_init() trampoline when booting with an OF client interface,
> - but that you have to provide yourself when using the flattened format.
> -
> - Recommended properties:
> -
> - - bootargs : This zero-terminated string is passed as the kernel
> - command line
> - - linux,stdout-path : This is the full path to your standard
> - console device if any. Typically, if you have serial devices on
> - your board, you may want to put the full path to the one set as
> - the default console in the firmware here, for the kernel to pick
> - it up as its own default console.
> -
> - Note that u-boot creates and fills in the chosen node for platforms
> - that use it.
> -
> - (Note: a practice that is now obsolete was to include a property
> - under /chosen called interrupt-controller which had a phandle value
> - that pointed to the main interrupt controller)
> -
> - f) the /soc<SOCname> node
> -
> - This node is used to represent a system-on-a-chip (SoC) and must be
> - present if the processor is a SoC. The top-level soc node contains
> - information that is global to all devices on the SoC. The node name
> - should contain a unit address for the SoC, which is the base address
> - of the memory-mapped register set for the SoC. The name of an SoC
> - node should start with "soc", and the remainder of the name should
> - represent the part number for the soc. For example, the MPC8540's
> - soc node would be called "soc8540".
> -
> - Required properties:
> -
> - - ranges : Should be defined as specified in 1) to describe the
> - translation of SoC addresses for memory mapped SoC registers.
> - - bus-frequency: Contains the bus frequency for the SoC node.
> - Typically, the value of this field is filled in by the boot
> - loader.
> - - compatible : Exact model of the SoC
> -
> -
> - Recommended properties:
> -
> - - reg : This property defines the address and size of the
> - memory-mapped registers that are used for the SOC node itself.
> - It does not include the child device registers - these will be
> - defined inside each child node. The address specified in the
> - "reg" property should match the unit address of the SOC node.
> - - #address-cells : Address representation for "soc" devices. The
> - format of this field may vary depending on whether or not the
> - device registers are memory mapped. For memory mapped
> - registers, this field represents the number of cells needed to
> - represent the address of the registers. For SOCs that do not
> - use MMIO, a special address format should be defined that
> - contains enough cells to represent the required information.
> - See 1) above for more details on defining #address-cells.
> - - #size-cells : Size representation for "soc" devices
> - - #interrupt-cells : Defines the width of cells used to represent
> - interrupts. Typically this value is <2>, which includes a
> - 32-bit number that represents the interrupt number, and a
> - 32-bit number that represents the interrupt sense and level.
> - This field is only needed if the SOC contains an interrupt
> - controller.
> -
> - The SOC node may contain child nodes for each SOC device that the
> - platform uses. Nodes should not be created for devices which exist
> - on the SOC but are not used by a particular platform. See chapter VI
> - for more information on how to specify devices that are part of a SOC.
> -
> - Example SOC node for the MPC8540:
> -
> - soc8540@...00000 {
> - #address-cells = <1>;
> - #size-cells = <1>;
> - #interrupt-cells = <2>;
> - device_type = "soc";
> - ranges = <0x00000000 0xe0000000 0x00100000>
> - reg = <0xe0000000 0x00003000>;
> - bus-frequency = <0>;
> - }
> -
> -
> -
> -IV - "dtc", the device tree compiler
> -====================================
> -
> -
> -dtc source code can be found at
> -<http://git.jdl.com/gitweb/?p=dtc.git>
> -
> -WARNING: This version is still in early development stage; the
> -resulting device-tree "blobs" have not yet been validated with the
> -kernel. The current generated block lacks a useful reserve map (it will
> -be fixed to generate an empty one, it's up to the bootloader to fill
> -it up) among others. The error handling needs work, bugs are lurking,
> -etc...
> -
> -dtc basically takes a device-tree in a given format and outputs a
> -device-tree in another format. The currently supported formats are:
> -
> - Input formats:
> - -------------
> -
> - - "dtb": "blob" format, that is a flattened device-tree block
> - with
> - header all in a binary blob.
> - - "dts": "source" format. This is a text file containing a
> - "source" for a device-tree. The format is defined later in this
> - chapter.
> - - "fs" format. This is a representation equivalent to the
> - output of /proc/device-tree, that is nodes are directories and
> - properties are files
> -
> - Output formats:
> - ---------------
> -
> - - "dtb": "blob" format
> - - "dts": "source" format
> - - "asm": assembly language file. This is a file that can be
> - sourced by gas to generate a device-tree "blob". That file can
> - then simply be added to your Makefile. Additionally, the
> - assembly file exports some symbols that can be used.
> -
> -
> -The syntax of the dtc tool is
> -
> - dtc [-I <input-format>] [-O <output-format>]
> - [-o output-filename] [-V output_version] input_filename
> -
> -
> -The "output_version" defines what version of the "blob" format will be
> -generated. Supported versions are 1,2,3 and 16. The default is
> -currently version 3 but that may change in the future to version 16.
> -
> -Additionally, dtc performs various sanity checks on the tree, like the
> -uniqueness of linux, phandle properties, validity of strings, etc...
> -
> -The format of the .dts "source" file is "C" like, supports C and C++
> -style comments.
> -
> -/ {
> -}
> -
> -The above is the "device-tree" definition. It's the only statement
> -supported currently at the toplevel.
> -
> -/ {
> - property1 = "string_value"; /* define a property containing a 0
> - * terminated string
> - */
> -
> - property2 = <0x1234abcd>; /* define a property containing a
> - * numerical 32-bit value (hexadecimal)
> - */
> -
> - property3 = <0x12345678 0x12345678 0xdeadbeef>;
> - /* define a property containing 3
> - * numerical 32-bit values (cells) in
> - * hexadecimal
> - */
> - property4 = [0x0a 0x0b 0x0c 0x0d 0xde 0xea 0xad 0xbe 0xef];
> - /* define a property whose content is
> - * an arbitrary array of bytes
> - */
> -
> - childnode@...ress { /* define a child node named "childnode"
> - * whose unit name is "childnode at
> - * address"
> - */
> -
> - childprop = "hello\n"; /* define a property "childprop" of
> - * childnode (in this case, a string)
> - */
> - };
> -};
> -
> -Nodes can contain other nodes etc... thus defining the hierarchical
> -structure of the tree.
> -
> -Strings support common escape sequences from C: "\n", "\t", "\r",
> -"\(octal value)", "\x(hex value)".
> -
> -It is also suggested that you pipe your source file through cpp (gcc
> -preprocessor) so you can use #include's, #define for constants, etc...
> -
> -Finally, various options are planned but not yet implemented, like
> -automatic generation of phandles, labels (exported to the asm file so
> -you can point to a property content and change it easily from whatever
> -you link the device-tree with), label or path instead of numeric value
> -in some cells to "point" to a node (replaced by a phandle at compile
> -time), export of reserve map address to the asm file, ability to
> -specify reserve map content at compile time, etc...
> -
> -We may provide a .h include file with common definitions of that
> -proves useful for some properties (like building PCI properties or
> -interrupt maps) though it may be better to add a notion of struct
> -definitions to the compiler...
> -
> -
> -V - Recommendations for a bootloader
> -====================================
> -
> -
> -Here are some various ideas/recommendations that have been proposed
> -while all this has been defined and implemented.
> -
> - - The bootloader may want to be able to use the device-tree itself
> - and may want to manipulate it (to add/edit some properties,
> - like physical memory size or kernel arguments). At this point, 2
> - choices can be made. Either the bootloader works directly on the
> - flattened format, or the bootloader has its own internal tree
> - representation with pointers (similar to the kernel one) and
> - re-flattens the tree when booting the kernel. The former is a bit
> - more difficult to edit/modify, the later requires probably a bit
> - more code to handle the tree structure. Note that the structure
> - format has been designed so it's relatively easy to "insert"
> - properties or nodes or delete them by just memmoving things
> - around. It contains no internal offsets or pointers for this
> - purpose.
> -
> - - An example of code for iterating nodes & retrieving properties
> - directly from the flattened tree format can be found in the kernel
> - file drivers/of/fdt.c. Look at the of_scan_flat_dt() function,
> - its usage in early_init_devtree(), and the corresponding various
> - early_init_dt_scan_*() callbacks. That code can be re-used in a
> - GPL bootloader, and as the author of that code, I would be happy
> - to discuss possible free licensing to any vendor who wishes to
> - integrate all or part of this code into a non-GPL bootloader.
> - (reference needed; who is 'I' here? ---gcl Jan 31, 2011)
> -
> -
> -
> -VI - System-on-a-chip devices and nodes
> -=======================================
> -
> -Many companies are now starting to develop system-on-a-chip
> -processors, where the processor core (CPU) and many peripheral devices
> -exist on a single piece of silicon. For these SOCs, an SOC node
> -should be used that defines child nodes for the devices that make
> -up the SOC. While platforms are not required to use this model in
> -order to boot the kernel, it is highly encouraged that all SOC
> -implementations define as complete a flat-device-tree as possible to
> -describe the devices on the SOC. This will allow for the
> -genericization of much of the kernel code.
> -
> -
> -1) Defining child nodes of an SOC
> ----------------------------------
> -
> -Each device that is part of an SOC may have its own node entry inside
> -the SOC node. For each device that is included in the SOC, the unit
> -address property represents the address offset for this device's
> -memory-mapped registers in the parent's address space. The parent's
> -address space is defined by the "ranges" property in the top-level soc
> -node. The "reg" property for each node that exists directly under the
> -SOC node should contain the address mapping from the child address space
> -to the parent SOC address space and the size of the device's
> -memory-mapped register file.
> -
> -For many devices that may exist inside an SOC, there are predefined
> -specifications for the format of the device tree node. All SOC child
> -nodes should follow these specifications, except where noted in this
> -document.
> -
> -See appendix A for an example partial SOC node definition for the
> -MPC8540.
> -
> -
> -2) Representing devices without a current OF specification
> -----------------------------------------------------------
> -
> -Currently, there are many devices on SoCs that do not have a standard
> -representation defined as part of the Open Firmware specifications,
> -mainly because the boards that contain these SoCs are not currently
> -booted using Open Firmware. Binding documentation for new devices
> -should be added to the Documentation/devicetree/bindings directory.
> -That directory will expand as device tree support is added to more and
> -more SoCs.
> -
> -
> -VII - Specifying interrupt information for devices
> -===================================================
> -
> -The device tree represents the buses and devices of a hardware
> -system in a form similar to the physical bus topology of the
> -hardware.
> -
> -In addition, a logical 'interrupt tree' exists which represents the
> -hierarchy and routing of interrupts in the hardware.
> -
> -The interrupt tree model is fully described in the
> -document "Open Firmware Recommended Practice: Interrupt
> -Mapping Version 0.9". The document is available at:
> -<http://www.devicetree.org/open-firmware/practice/>
> -
> -1) interrupts property
> -----------------------
> -
> -Devices that generate interrupts to a single interrupt controller
> -should use the conventional OF representation described in the
> -OF interrupt mapping documentation.
> -
> -Each device which generates interrupts must have an 'interrupt'
> -property. The interrupt property value is an arbitrary number of
> -of 'interrupt specifier' values which describe the interrupt or
> -interrupts for the device.
> -
> -The encoding of an interrupt specifier is determined by the
> -interrupt domain in which the device is located in the
> -interrupt tree. The root of an interrupt domain specifies in
> -its #interrupt-cells property the number of 32-bit cells
> -required to encode an interrupt specifier. See the OF interrupt
> -mapping documentation for a detailed description of domains.
> -
> -For example, the binding for the OpenPIC interrupt controller
> -specifies an #interrupt-cells value of 2 to encode the interrupt
> -number and level/sense information. All interrupt children in an
> -OpenPIC interrupt domain use 2 cells per interrupt in their interrupts
> -property.
> -
> -The PCI bus binding specifies a #interrupt-cells value of 1 to encode
> -which interrupt pin (INTA,INTB,INTC,INTD) is used.
> -
> -2) interrupt-parent property
> -----------------------------
> -
> -The interrupt-parent property is specified to define an explicit
> -link between a device node and its interrupt parent in
> -the interrupt tree. The value of interrupt-parent is the
> -phandle of the parent node.
> -
> -If the interrupt-parent property is not defined for a node, its
> -interrupt parent is assumed to be an ancestor in the node's
> -_device tree_ hierarchy.
> -
> -3) OpenPIC Interrupt Controllers
> ---------------------------------
> -
> -OpenPIC interrupt controllers require 2 cells to encode
> -interrupt information. The first cell defines the interrupt
> -number. The second cell defines the sense and level
> -information.
> -
> -Sense and level information should be encoded as follows:
> -
> - 0 = low to high edge sensitive type enabled
> - 1 = active low level sensitive type enabled
> - 2 = active high level sensitive type enabled
> - 3 = high to low edge sensitive type enabled
> -
> -4) ISA Interrupt Controllers
> -----------------------------
> -
> -ISA PIC interrupt controllers require 2 cells to encode
> -interrupt information. The first cell defines the interrupt
> -number. The second cell defines the sense and level
> -information.
> -
> -ISA PIC interrupt controllers should adhere to the ISA PIC
> -encodings listed below:
> -
> - 0 = active low level sensitive type enabled
> - 1 = active high level sensitive type enabled
> - 2 = high to low edge sensitive type enabled
> - 3 = low to high edge sensitive type enabled
>
> VIII - Specifying Device Power Management Information (sleep property)
> ===================================================================
> @@ -1386,6 +491,7 @@ reasonably grouped in this manner, then create a virtual sleep controller
> (similar to an interrupt nexus, except that defining a standardized
> sleep-map should wait until its necessity is demonstrated).
>
> +
> IX - Specifying dma bus information
>
> Some devices may have DMA memory range shifted relatively to the beginning of
> @@ -1420,134 +526,3 @@ Optional property:
> - dma-ranges: <empty> value. if present - It means that DMA addresses
> translation has to be enabled for this device.
> - dma-coherent: Present if dma operations are coherent
> -
> -Example:
> -soc {
> - compatible = "ti,keystone","simple-bus";
> - ranges = <0x0 0x0 0x0 0xc0000000>;
> - dma-ranges = <0x80000000 0x8 0x00000000 0x80000000>;
> -
> - [...]
> -
> - usb: usb@...0000 {
> - compatible = "ti,keystone-dwc3";
> -
> - [...]
> - dma-coherent;
> - };
> -};
> -
> -Appendix A - Sample SOC node for MPC8540
> -========================================
> -
> - soc@...00000 {
> - #address-cells = <1>;
> - #size-cells = <1>;
> - compatible = "fsl,mpc8540-ccsr", "simple-bus";
> - device_type = "soc";
> - ranges = <0x00000000 0xe0000000 0x00100000>
> - bus-frequency = <0>;
> - interrupt-parent = <&pic>;
> -
> - ethernet@...00 {
> - #address-cells = <1>;
> - #size-cells = <1>;
> - device_type = "network";
> - model = "TSEC";
> - compatible = "gianfar", "simple-bus";
> - reg = <0x24000 0x1000>;
> - local-mac-address = [ 0x00 0xE0 0x0C 0x00 0x73 0x00 ];
> - interrupts = <0x29 2 0x30 2 0x34 2>;
> - phy-handle = <&phy0>;
> - sleep = <&pmc 0x00000080>;
> - ranges;
> -
> - mdio@...20 {
> - reg = <0x24520 0x20>;
> - compatible = "fsl,gianfar-mdio";
> -
> - phy0: ethernet-phy@0 {
> - interrupts = <5 1>;
> - reg = <0>;
> - };
> -
> - phy1: ethernet-phy@1 {
> - interrupts = <5 1>;
> - reg = <1>;
> - };
> -
> - phy3: ethernet-phy@3 {
> - interrupts = <7 1>;
> - reg = <3>;
> - };
> - };
> - };
> -
> - ethernet@...00 {
> - device_type = "network";
> - model = "TSEC";
> - compatible = "gianfar";
> - reg = <0x25000 0x1000>;
> - local-mac-address = [ 0x00 0xE0 0x0C 0x00 0x73 0x01 ];
> - interrupts = <0x13 2 0x14 2 0x18 2>;
> - phy-handle = <&phy1>;
> - sleep = <&pmc 0x00000040>;
> - };
> -
> - ethernet@...00 {
> - device_type = "network";
> - model = "FEC";
> - compatible = "gianfar";
> - reg = <0x26000 0x1000>;
> - local-mac-address = [ 0x00 0xE0 0x0C 0x00 0x73 0x02 ];
> - interrupts = <0x41 2>;
> - phy-handle = <&phy3>;
> - sleep = <&pmc 0x00000020>;
> - };
> -
> - serial@...0 {
> - #address-cells = <1>;
> - #size-cells = <1>;
> - compatible = "fsl,mpc8540-duart", "simple-bus";
> - sleep = <&pmc 0x00000002>;
> - ranges;
> -
> - serial@...0 {
> - device_type = "serial";
> - compatible = "ns16550";
> - reg = <0x4500 0x100>;
> - clock-frequency = <0>;
> - interrupts = <0x42 2>;
> - };
> -
> - serial@...0 {
> - device_type = "serial";
> - compatible = "ns16550";
> - reg = <0x4600 0x100>;
> - clock-frequency = <0>;
> - interrupts = <0x42 2>;
> - };
> - };
> -
> - pic: pic@...00 {
> - interrupt-controller;
> - #address-cells = <0>;
> - #interrupt-cells = <2>;
> - reg = <0x40000 0x40000>;
> - compatible = "chrp,open-pic";
> - device_type = "open-pic";
> - };
> -
> - i2c@...0 {
> - interrupts = <0x43 2>;
> - reg = <0x3000 0x100>;
> - compatible = "fsl-i2c";
> - dfsrr;
> - sleep = <&pmc 0x00000004>;
> - };
> -
> - pmc: power@...70 {
> - compatible = "fsl,mpc8540-pmc", "fsl,mpc8548-pmc";
> - reg = <0xe0070 0x20>;
> - };
> - };
>
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