1 ========================
2 The PowerPC boot wrapper
3 ========================
4
5 Copyright (C) Secret Lab Technologies Ltd.
6
7 PowerPC image targets compresses and wraps the
8 a boot wrapper to make it usable by the system
9 standard PowerPC firmware interface, so the bo
10 be adaptable for each kind of image that needs
11
12 The boot wrapper can be found in the arch/powe
13 Makefile in that directory has targets for all
14 The different image types are used to support
15 interfaces found on PowerPC platforms. OpenFi
16 used firmware type on general purpose PowerPC
17 others. U-Boot is typically found on embedded
18 are a handful of other firmware implementation
19 firmware interface requires a different image
20
21 The boot wrapper is built from the makefile in
22 it uses the wrapper script (arch/powerpc/boot/
23 image. The details of the build system is dis
24 Currently, the following image format targets
25
26 ==================== ======================
27 cuImage.%: Backwards compatible u
28 U-Boot (for versions t
29 tree). This image emb
30 the image. The boot w
31 are all embedded insid
32 with boot wrapper code
33 bd_info structure and
34 tree before jumping in
35
36 Because of the series
37 bd_info structure used
38 cuImages are platform
39 U-Boot platform has a
40 which populates the em
41 from the platform spec
42 specific cuImage platf
43 `arch/powerpc/boot/cub
44 cuImage init code for
45 the wrapper structure.
46
47 dtbImage.%: Similar to zImage, exc
48 inside the image inste
49 output image file can
50 binary depending on th
51
52 dtbImages are used on
53 interface for passing
54 dtbImages are similar
55 dtbImages have platfor
56 data from the board fi
57 talk to the firmware a
58
59 PlayStation 3 support
60 Planet boards using th
61 specific initializatio
62 file named arch/powerp
63 can be overridden by t
64
65 simpleImage.%: Firmware independent c
66 depend on any particul
67 a device tree blob. T
68 can be loaded to any l
69 Firmware cannot pass a
70 kernel with this image
71 the embedded device tr
72
73 treeImage.%; Image format for used
74 on some ppc4xx hardwar
75 tree blob inside the i
76
77 uImage: Native image format us
78 does not add any boot
79 vmlinux in the uImage
80 requires a version of
81 a device tree to the k
82 version of U-Boot, the
83 instead.
84
85 zImage.%: Image format which doe
86 Used by OpenFirmware a
87 which are able to supp
88 expects firmware to pr
89 Typically, if you have
90 hardware then you want
91 ==================== ======================
92
93 Image types which embed a device tree blob (si
94 and cuImage) all generate the device tree blob
95 arch/powerpc/boot/dts/ directory. The Makefil
96 tree source based on the name of the target.
97 built with 'make treeImage.walnut', then the b
98 arch/powerpc/boot/dts/walnut.dts to build tree
99
100 Two special targets called 'zImage' and 'zImag
101 targets build all the default images as select
102 Default images are selected by the boot wrappe
103 (arch/powerpc/boot/Makefile) by adding targets
104 at the Makefile to see which default image tar
105
106 How it is built
107 ---------------
108 arch/powerpc is designed to support multiplatf
109 that a single vmlinux image can be booted on m
110 It also means that the boot wrapper must be ab
111 images on a single build. The design decision
112 conditional compilation code (#ifdef, etc) in
113 All of the boot wrapper pieces are buildable a
114 kernel configuration. Building all the wrappe
115 also ensures that obscure parts of the wrapper
116 tested in a large variety of environments.
117
118 The wrapper is adapted for different image typ
119 just the wrapper bits that are appropriate for
120 script' (found in arch/powerpc/boot/wrapper) i
121 is responsible for selecting the correct wrapp
122 The arguments are well documented in the scrip
123 are not repeated here. However, it is worth m
124 uses the -p (platform) argument as the main me
125 bits to compile in. Look for the large 'case
126 middle of the script. This is also the place
127 can be selected by changing the link order.
128
129 In particular, care should be taken when worki
130 wrapper bits are very board specific and care
131 the target you are trying to build is supporte
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