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authorStephen Warren <swarren@nvidia.com>2016-06-17 09:43:58 -0600
committerSimon Glass <sjg@chromium.org>2016-06-19 17:05:55 -0600
commit89c1e2da78f82a09685006291ce8bb44f635fa25 (patch)
tree4962e19a65e7cf8caf997ee92ec16030dead512a /doc
parent0f67e2395be44db2c1bef17b6ada2e46221908ed (diff)
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Add a reset driver framework/uclass
A reset controller is a hardware module that controls reset signals that affect other hardware modules or chips. This patch defines a standard API that connects reset clients (i.e. the drivers for devices affected by reset signals) to drivers for reset controllers/providers. Initially, DT is the only supported method for connecting the two. The DT binding specification (reset.txt) was taken from Linux kernel v4.5's Documentation/devicetree/bindings/reset/reset.txt. Signed-off-by: Stephen Warren <swarren@nvidia.com> Acked-by: Simon Glass <sjg@chromium.org>
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diff --git a/doc/device-tree-bindings/reset/reset.txt b/doc/device-tree-bindings/reset/reset.txt
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+= 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.