mirror of
https://github.com/brain-hackers/u-boot-brain
synced 2024-08-20 17:08:52 +09:00
76 lines
2.9 KiB
Plaintext
76 lines
2.9 KiB
Plaintext
![]() |
= Reset Signal Device Tree Bindings =
|
||
|
|
||
|
This binding is intended to represent the hardware reset signals present
|
||
|
internally in most IC (SoC, FPGA, ...) designs. Reset signals for whole
|
||
|
standalone chips are most likely better represented as GPIOs, although there
|
||
|
are likely to be exceptions to this rule.
|
||
|
|
||
|
Hardware blocks typically receive a reset signal. This signal is generated by
|
||
|
a reset provider (e.g. power management or clock module) and received by a
|
||
|
reset consumer (the module being reset, or a module managing when a sub-
|
||
|
ordinate module is reset). This binding exists to represent the provider and
|
||
|
consumer, and provide a way to couple the two together.
|
||
|
|
||
|
A reset signal is represented by the phandle of the provider, plus a reset
|
||
|
specifier - a list of DT cells that represents the reset signal within the
|
||
|
provider. The length (number of cells) and semantics of the reset specifier
|
||
|
are dictated by the binding of the reset provider, although common schemes
|
||
|
are described below.
|
||
|
|
||
|
A word on where to place reset signal consumers in device tree: It is possible
|
||
|
in hardware for a reset signal to affect multiple logically separate HW blocks
|
||
|
at once. In this case, it would be unwise to represent this reset signal in
|
||
|
the DT node of each affected HW block, since if activated, an unrelated block
|
||
|
may be reset. Instead, reset signals should be represented in the DT node
|
||
|
where it makes most sense to control it; this may be a bus node if all
|
||
|
children of the bus are affected by the reset signal, or an individual HW
|
||
|
block node for dedicated reset signals. The intent of this binding is to give
|
||
|
appropriate software access to the reset signals in order to manage the HW,
|
||
|
rather than to slavishly enumerate the reset signal that affects each HW
|
||
|
block.
|
||
|
|
||
|
= Reset providers =
|
||
|
|
||
|
Required properties:
|
||
|
#reset-cells: Number of cells in a reset specifier; Typically 0 for nodes
|
||
|
with a single reset output and 1 for nodes with multiple
|
||
|
reset outputs.
|
||
|
|
||
|
For example:
|
||
|
|
||
|
rst: reset-controller {
|
||
|
#reset-cells = <1>;
|
||
|
};
|
||
|
|
||
|
= Reset consumers =
|
||
|
|
||
|
Required properties:
|
||
|
resets: List of phandle and reset specifier pairs, one pair
|
||
|
for each reset signal that affects the device, or that the
|
||
|
device manages. Note: if the reset provider specifies '0' for
|
||
|
#reset-cells, then only the phandle portion of the pair will
|
||
|
appear.
|
||
|
|
||
|
Optional properties:
|
||
|
reset-names: List of reset signal name strings sorted in the same order as
|
||
|
the resets property. Consumers drivers will use reset-names to
|
||
|
match reset signal names with reset specifiers.
|
||
|
|
||
|
For example:
|
||
|
|
||
|
device {
|
||
|
resets = <&rst 20>;
|
||
|
reset-names = "reset";
|
||
|
};
|
||
|
|
||
|
This represents a device with a single reset signal named "reset".
|
||
|
|
||
|
bus {
|
||
|
resets = <&rst 10> <&rst 11> <&rst 12> <&rst 11>;
|
||
|
reset-names = "i2s1", "i2s2", "dma", "mixer";
|
||
|
};
|
||
|
|
||
|
This represents a bus that controls the reset signal of each of four sub-
|
||
|
ordinate devices. Consider for example a bus that fails to operate unless no
|
||
|
child device has reset asserted.
|