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1Flash partitions in device tree
2===============================
3
4Flash devices can be partitioned into one or more functional ranges (e.g. "boot
5code", "nvram", "kernel").
6
7Different devices may be partitioned in a different ways. Some may use a fixed
8flash layout set at production time. Some may use on-flash table that describes
9the geometry and naming/purpose of each functional region. It is also possible
10to see these methods mixed.
11
12To assist system software in locating partitions, we allow describing which
13method is used for a given flash device. To describe the method there should be
14a subnode of the flash device that is named 'partitions'. It must have a
15'compatible' property, which is used to identify the method to use.
16
17We currently only document a binding for fixed layouts.
18
19
20Fixed Partitions
21================
22
23Partitions can be represented by sub-nodes of a flash device. This can be used
24on platforms which have strong conventions about which portions of a flash are
25used for what purposes, but which don't use an on-flash partition table such
26as RedBoot.
27
28The partition table should be a subnode of the flash node and should be named
29'partitions'. This node should have the following property:
30- compatible : (required) must be "fixed-partitions"
31Partitions are then defined in subnodes of the partitions node.
32
33For backwards compatibility partitions as direct subnodes of the flash device are
34supported. This use is discouraged.
35NOTE: also for backwards compatibility, direct subnodes that have a compatible
36string are not considered partitions, as they may be used for other bindings.
37
38#address-cells & #size-cells must both be present in the partitions subnode of the
39flash device. There are two valid values for both:
40<1>: for partitions that require a single 32-bit cell to represent their
41 size/address (aka the value is below 4 GiB)
42<2>: for partitions that require two 32-bit cells to represent their
43 size/address (aka the value is 4 GiB or greater).
44
45Required properties:
46- reg : The partition's offset and size within the flash
47
48Optional properties:
49- label : The label / name for this partition. If omitted, the label is taken
50 from the node name (excluding the unit address).
51- read-only : This parameter, if present, is a hint to Linux that this
52 partition should only be mounted read-only. This is usually used for flash
53 partitions containing early-boot firmware images or data which should not be
54 clobbered.
55- lock : Do not unlock the partition at initialization time (not supported on
56 all devices)
57
58Examples:
59
60
61flash@0 {
62 partitions {
63 compatible = "fixed-partitions";
64 #address-cells = <1>;
65 #size-cells = <1>;
66
67 partition@0 {
68 label = "u-boot";
69 reg = <0x0000000 0x100000>;
70 read-only;
71 };
72
73 uimage@100000 {
74 reg = <0x0100000 0x200000>;
75 };
76 };
77};
78
79flash@1 {
80 partitions {
81 compatible = "fixed-partitions";
82 #address-cells = <1>;
83 #size-cells = <2>;
84
85 /* a 4 GiB partition */
86 partition@0 {
87 label = "filesystem";
88 reg = <0x00000000 0x1 0x00000000>;
89 };
90 };
91};
92
93flash@2 {
94 partitions {
95 compatible = "fixed-partitions";
96 #address-cells = <2>;
97 #size-cells = <2>;
98
99 /* an 8 GiB partition */
100 partition@0 {
101 label = "filesystem #1";
102 reg = <0x0 0x00000000 0x2 0x00000000>;
103 };
104
105 /* a 4 GiB partition */
106 partition@200000000 {
107 label = "filesystem #2";
108 reg = <0x2 0x00000000 0x1 0x00000000>;
109 };
110 };
111};