UBootCmdFDT < DULG

%SECTION0{name=UBootCmdFDT}% Flattened Device Tree support

U-Boot is capable of quite comprehensive handling of the flattened
device tree blob, implemented by the =fdt= family of commands:

%INCLUDE{DULGData_%BOARD%.UBootFDTCmdHelp}%

%SECTION1{name=UBootCmdFDTAddr}% fdt addr - select FDT to work on

First, the blob that is to be operated on should be stored in memory,
and U-Boot has to be informed about its location by the =fdt addr=
command. Once this command has been issued, all subsequent =fdt=
handling commands will use the blob stored at the given address. This
address can be changed later on by issuing =fdt addr= or =fdt move=
command. Here's how to load the blob into memory and tell U-Boot its
location:

%INCLUDE{DULGData_%BOARD%.UBootFDTCmdAddr}%

%SECTION1{name=UBootCmdFDTPrint}% fdt list - print one level

Having selected the device tree stored in the blob just loaded, we can
inspect its contents.  As an FDT usually is quite extensive, it is
easier to get information about the structure by looking at selected
levels rather than full hierarchies.  =fdt list= allows us to do
exactly this.  Let's have a look at the hierarchy one level below the
=cpus= node:

%INCLUDE{DULGData_%BOARD%.UBootFDTCmdList}%

%SECTION1{name=UBootCmdFDTPrint}% fdt print - recursive print

To print a complete subtree we use =fdt print=.  In comparison to the
previous example it is obvious that the whole subtree is printed:

%INCLUDE{DULGData_%BOARD%.UBootFDTCmdPrint}%

%SECTION1{name=UBootCmdFDTCreateNode}% fdt mknode - create new nodes

=fdt mknode= can be used to attach a new node to the tree. We will use
the =fdt list= command to verify that the new node has been created
and that it is empty:

%INCLUDE{DULGData_%BOARD%.UBootFDTCmdCreateNode}%

%SECTION1{name=UBootCmdFDTCmdCreateProperty}% fdt set - set node properties

Now, let's create a property at the newly created node; again we'll
use =fdt list= for verification:

%INCLUDE{DULGData_%BOARD%.UBootFDTCmdCreateProperty}%

%SECTION1{name=UBootCmdFDTCmdRemove}% fdt rm - remove nodes or properties

The =fdt rm= command is used to remove nodes and properties.  Let's
delete the test property created in the previous paragraph and verify
the results:

%INCLUDE{DULGData_%BOARD%.UBootFDTCmdRemove}%

%SECTION1{name=UBootCmdFDTCmdMove}% fdt move - move FDT blob to new address

To move the blob from one memory location to another we will use the
=fdt move= command. Besides moving the blob, it makes the new address
the "active" one - similar to =fdt addr=:

%INCLUDE{DULGData_%BOARD%.UBootFDTCmdMove}%

%SECTION1{name=UBootCmdFDTCmdChosen}% fdt chosen - fixup dynamic info

One of the modifications made by U-Boot to the blob before passing it
to the kernel is the addition of the =/chosen= node. Linux 2.6
Documentation/powerpc/booting-without-of.txt says that this node is
used to store "some variable environment information, like the
arguments, or the default input/output devices." To force U-Boot to
add the =/chosen= node to the current blob, =fdt chosen= command can
be used. Let's now verify its operation:

%INCLUDE{DULGData_%BOARD%.UBootFDTCmdChosen}%

Note: =fdt boardsetup= performs board-specific blob updates, most
commonly setting clock frequencies, etc. Discovering its operation is
left as an excercise for the reader.
5.9.6. Environment Variables Commands		1. Abstract		5.9.8. Special Commands
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