c66ec88fed
git-subtree-dir: sys/contrib/device-tree git-subtree-mainline:94611a8388git-subtree-split:5ee353c36d
76 lines
2.9 KiB
Plaintext
76 lines
2.9 KiB
Plaintext
= Reset Signal Device Tree Bindings =
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This binding is intended to represent the hardware reset signals present
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internally in most IC (SoC, FPGA, ...) designs. Reset signals for whole
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standalone chips are most likely better represented as GPIOs, although there
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are likely to be exceptions to this rule.
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Hardware blocks typically receive a reset signal. This signal is generated by
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a reset provider (e.g. power management or clock module) and received by a
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reset consumer (the module being reset, or a module managing when a sub-
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ordinate module is reset). This binding exists to represent the provider and
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consumer, and provide a way to couple the two together.
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A reset signal is represented by the phandle of the provider, plus a reset
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specifier - a list of DT cells that represents the reset signal within the
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provider. The length (number of cells) and semantics of the reset specifier
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are dictated by the binding of the reset provider, although common schemes
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are described below.
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A word on where to place reset signal consumers in device tree: It is possible
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in hardware for a reset signal to affect multiple logically separate HW blocks
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at once. In this case, it would be unwise to represent this reset signal in
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the DT node of each affected HW block, since if activated, an unrelated block
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may be reset. Instead, reset signals should be represented in the DT node
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where it makes most sense to control it; this may be a bus node if all
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children of the bus are affected by the reset signal, or an individual HW
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block node for dedicated reset signals. The intent of this binding is to give
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appropriate software access to the reset signals in order to manage the HW,
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rather than to slavishly enumerate the reset signal that affects each HW
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block.
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= Reset providers =
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Required properties:
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#reset-cells: Number of cells in a reset specifier; Typically 0 for nodes
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with a single reset output and 1 for nodes with multiple
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reset outputs.
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For example:
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rst: reset-controller {
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#reset-cells = <1>;
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};
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= Reset consumers =
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Required properties:
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resets: List of phandle and reset specifier pairs, one pair
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for each reset signal that affects the device, or that the
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device manages. Note: if the reset provider specifies '0' for
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#reset-cells, then only the phandle portion of the pair will
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appear.
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Optional properties:
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reset-names: List of reset signal name strings sorted in the same order as
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the resets property. Consumers drivers will use reset-names to
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match reset signal names with reset specifiers.
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For example:
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device {
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resets = <&rst 20>;
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reset-names = "reset";
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};
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This represents a device with a single reset signal named "reset".
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bus {
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resets = <&rst 10> <&rst 11> <&rst 12> <&rst 11>;
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reset-names = "i2s1", "i2s2", "dma", "mixer";
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};
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This represents a bus that controls the reset signal of each of four sub-
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ordinate devices. Consider for example a bus that fails to operate unless no
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child device has reset asserted.
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