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Commit 0e0293c8 authored by David Gibson's avatar David Gibson Committed by Paul Mackerras
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[POWERPC] Update documentation for flat device tree format v17 



This patch updates booting-without-of.txt to describe version 17 of
the flattened device tree format.  Version 17 is a small, backwards
compatible change from version 16, adding an extra field giving the
size of the device tree's structure block.  At this time, the kernel
has no use for the extra information, however its presence can make
life easier for bootloaders or other software manipulating the tree.

In addition this patch adds information on the size_dt_strings field
of the device tree header, present since version 3 of the flattened
tree format, but omitted from the documentation.  It also makes
changes to consistently refer to versions 16 and 17 as versions 16 and
17 in decimal, rather than version 0x10 which was occasionally used
for version 16 previously.

Finally, we also add the new field to the definition of the device
tree header structure in prom.h

Signed-off-by: default avatarDavid Gibson <david@gibson.dropbear.id.au>
Acked-by: default avatarJon Loeliger <jdl@freescale.com>
Signed-off-by: default avatarPaul Mackerras <paulus@samba.org>
parent a782a9e3

Documentation/powerpc/booting-without-of.txt

+23 −6
Original line number Diff line number Diff line
@@ -265,6 +265,9 @@ struct boot_param_header { 
                                           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:
@@ -335,10 +338,13 @@ struct boot_param_header { 
     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. You should always generate a structure of the highest

     version defined at the time of your implementation. Currently

     that is version 16, unless you explicitly aim at being backward

     compatible.

     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
@@ -347,7 +353,7 @@ struct boot_param_header { 
     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 0x10 if you generate a tree of version 0x10

     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
@@ -360,6 +366,17 @@ struct boot_param_header { 
     point (see further chapters for more informations 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
@@ -417,7 +434,7 @@ root node who has no parent. 
A node has 2 names. The actual node name is generally contained in a

property of type "name" in the node property list whose value is a

zero terminated string and is mandatory for version 1 to 3 of the

format definition (as it is in Open Firmware). Version 0x10 makes it

format definition (as it is in Open Firmware). Version 16 makes it

optional as it can generate it from the unit name defined below.



There is also a "unit name" that is used to differentiate nodes with

include/asm-powerpc/prom.h

+2 −0
Original line number Diff line number Diff line
@@ -59,6 +59,8 @@ struct boot_param_header 
	u32	boot_cpuid_phys;	/* Physical CPU id we're booting on */

	/* version 3 fields below */

	u32	dt_strings_size;	/* size of the DT strings block */

	/* version 17 fields below */

	u32	dt_struct_size;		/* size of the DT structure block */

};