158 lines
4.4 KiB
Plaintext
158 lines
4.4 KiB
Plaintext
Flash partitions in device tree
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===============================
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Flash devices can be partitioned into one or more functional ranges (e.g. "boot
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code", "nvram", "kernel").
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Different devices may be partitioned in a different ways. Some may use a fixed
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flash layout set at production time. Some may use on-flash table that describes
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the geometry and naming/purpose of each functional region. It is also possible
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to see these methods mixed.
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To assist system software in locating partitions, we allow describing which
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method is used for a given flash device. To describe the method there should be
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a subnode of the flash device that is named 'partitions'. It must have a
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'compatible' property, which is used to identify the method to use.
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When a single partition is represented with a DT node (it depends on a used
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format) it may also be described using above rules ('compatible' and optionally
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some extra properties / subnodes). It allows describing more complex,
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hierarchical (multi-level) layouts and should be used if there is some
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significant relation between partitions or some partition internally uses
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another partitioning method.
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Available bindings are listed in the "partitions" subdirectory.
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Fixed Partitions
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================
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Partitions can be represented by sub-nodes of a flash device. This can be used
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on platforms which have strong conventions about which portions of a flash are
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used for what purposes, but which don't use an on-flash partition table such
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as RedBoot.
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The partition table should be a subnode of the flash node and should be named
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'partitions'. This node should have the following property:
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- compatible : (required) must be "fixed-partitions"
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Partitions are then defined in subnodes of the partitions node.
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For backwards compatibility partitions as direct subnodes of the flash device are
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supported. This use is discouraged.
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NOTE: also for backwards compatibility, direct subnodes that have a compatible
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string are not considered partitions, as they may be used for other bindings.
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#address-cells & #size-cells must both be present in the partitions subnode of the
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flash device. There are two valid values for both:
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<1>: for partitions that require a single 32-bit cell to represent their
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size/address (aka the value is below 4 GiB)
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<2>: for partitions that require two 32-bit cells to represent their
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size/address (aka the value is 4 GiB or greater).
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Required properties:
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- reg : The partition's offset and size within the flash
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Optional properties:
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- label : The label / name for this partition. If omitted, the label is taken
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from the node name (excluding the unit address).
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- read-only : This parameter, if present, is a hint to Linux that this
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partition should only be mounted read-only. This is usually used for flash
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partitions containing early-boot firmware images or data which should not be
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clobbered.
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- lock : Do not unlock the partition at initialization time (not supported on
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all devices)
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Examples:
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flash@0 {
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partitions {
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compatible = "fixed-partitions";
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#address-cells = <1>;
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#size-cells = <1>;
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partition@0 {
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label = "u-boot";
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reg = <0x0000000 0x100000>;
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read-only;
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};
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uimage@100000 {
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reg = <0x0100000 0x200000>;
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};
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};
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};
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flash@1 {
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partitions {
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compatible = "fixed-partitions";
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#address-cells = <1>;
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#size-cells = <2>;
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/* a 4 GiB partition */
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partition@0 {
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label = "filesystem";
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reg = <0x00000000 0x1 0x00000000>;
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};
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};
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};
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flash@2 {
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partitions {
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compatible = "fixed-partitions";
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#address-cells = <2>;
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#size-cells = <2>;
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/* an 8 GiB partition */
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partition@0 {
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label = "filesystem #1";
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reg = <0x0 0x00000000 0x2 0x00000000>;
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};
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/* a 4 GiB partition */
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partition@200000000 {
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label = "filesystem #2";
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reg = <0x2 0x00000000 0x1 0x00000000>;
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};
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};
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};
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flash@3 {
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partitions {
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compatible = "fixed-partitions";
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#address-cells = <1>;
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#size-cells = <1>;
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partition@0 {
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label = "bootloader";
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reg = <0x000000 0x100000>;
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read-only;
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};
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firmware@100000 {
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label = "firmware";
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reg = <0x100000 0xe00000>;
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compatible = "brcm,trx";
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};
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calibration@f00000 {
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label = "calibration";
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reg = <0xf00000 0x100000>;
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compatible = "fixed-partitions";
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ranges = <0 0xf00000 0x100000>;
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#address-cells = <1>;
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#size-cells = <1>;
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partition@0 {
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label = "wifi0";
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reg = <0x000000 0x080000>;
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};
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partition@80000 {
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label = "wifi1";
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reg = <0x080000 0x080000>;
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};
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};
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};
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};
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