dt-bindings: mtd: make partitions doc a bit more generic
Currently the only documented partitioning is "fixed-partitions" but there are more methods in use that we may want to support in the future. Mention them and make it clear Fixed Partitions are just a single case. Signed-off-by: Brian Norris <computersforpeace@gmail.com> Signed-off-by: Rafał Miłecki <rafal@milecki.pl> Acked-by: Rob Herring <robh@kernel.org>
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Documentation/devicetree/bindings/mtd
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Representing flash partitions in devicetree
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Flash partitions in device tree
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===============================
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Partitions can be represented by sub-nodes of an mtd device. This can be used
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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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We currently only document a binding for fixed layouts.
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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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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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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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as RedBoot.
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The partition table should be a subnode of the mtd node and should be named
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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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'partitions'. This node should have the following property:
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- compatible : (required) must be "fixed-partitions"
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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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Partitions are then defined in subnodes of the partitions node.
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For backwards compatibility partitions as direct subnodes of the mtd device are
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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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supported. This use is discouraged.
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NOTE: also for backwards compatibility, direct subnodes that have a compatible
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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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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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#address-cells & #size-cells must both be present in the partitions subnode of the
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mtd device. There are two valid values for both:
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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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<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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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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<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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size/address (aka the value is 4 GiB or greater).
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Required properties:
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Required properties:
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- reg : The partition's offset and size within the mtd bank.
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- reg : The partition's offset and size within the flash
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Optional properties:
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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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- label : The label / name for this partition. If omitted, the label is taken
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