--- /dev/null
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+# Copyright (C) 2020 BAIKAL ELECTRONICS, JSC
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/clock/baikal,bt1-ccu-pll.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Baikal-T1 Clock Control Unit PLL
+
+maintainers:
+ - Serge Semin <fancer.lancer@gmail.com>
+
+description: |
+ Clocks Control Unit is the core of Baikal-T1 SoC System Controller
+ responsible for the chip subsystems clocking and resetting. The CCU is
+ connected with an external fixed rate oscillator, which signal is transformed
+ into clocks of various frequencies and then propagated to either individual
+ IP-blocks or to groups of blocks (clock domains). The transformation is done
+ by means of PLLs and gateable/non-gateable dividers embedded into the CCU.
+ It's logically divided into the next components:
+ 1) External oscillator (normally XTAL's 25 MHz crystal oscillator, but
+ in general can provide any frequency supported by the CCU PLLs).
+ 2) PLLs clocks generators (PLLs) - described in this binding file.
+ 3) AXI-bus clock dividers (AXI).
+ 4) System devices reference clock dividers (SYS).
+ which are connected with each other as shown on the next figure:
+
+ +---------------+
+ | Baikal-T1 CCU |
+ | +----+------|- MIPS P5600 cores
+ | +-|PLLs|------|- DDR controller
+ | | +----+ |
+ +----+ | | | | |
+ |XTAL|--|-+ | | +---+-|
+ +----+ | | | +-|AXI|-|- AXI-bus
+ | | | +---+-|
+ | | | |
+ | | +----+---+-|- APB-bus
+ | +-------|SYS|-|- Low-speed Devices
+ | +---+-|- High-speed Devices
+ +---------------+
+
+ Each CCU sub-block is represented as a separate dts-node and has an
+ individual driver to be bound with.
+
+ In order to create signals of wide range frequencies the external oscillator
+ output is primarily connected to a set of CCU PLLs. There are five PLLs
+ to create a clock for the MIPS P5600 cores, the embedded DDR controller,
+ SATA, Ethernet and PCIe domains. The last three domains though named by the
+ biggest system interfaces in fact include nearly all of the rest SoC
+ peripherals. Each of the PLLs is based on True Circuits TSMC CLN28HPM core
+ with an interface wrapper (so called safe PLL' clocks switcher) to simplify
+ the PLL configuration procedure. The PLLs work as depicted on the next
+ diagram:
+
+ +--------------------------+
+ | |
+ +-->+---+ +---+ +---+ | +---+ 0|\
+ CLKF--->|/NF|--->|PFD|...|VCO|-+->|/OD|--->| |
+ +---+ +->+---+ +---+ /->+---+ | |--->CLKOUT
+ CLKOD---------C----------------+ 1| |
+ +--------C--------------------------->|/
+ | | ^
+ Rclk-+->+---+ | |
+ CLKR--->|/NR|-+ |
+ +---+ |
+ BYPASS--------------------------------------+
+ BWADJ--->
+
+ where Rclk is the reference clock coming from XTAL, NR - reference clock
+ divider, NF - PLL clock multiplier, OD - VCO output clock divider, CLKOUT -
+ output clock, BWADJ is the PLL bandwidth adjustment parameter. At this moment
+ the binding supports the PLL dividers configuration in accordance with a
+ requested rate, while bypassing and bandwidth adjustment settings can be
+ added in future if it gets to be necessary.
+
+ The PLLs CLKOUT is then either directly connected with the corresponding
+ clocks consumer (like P5600 cores or DDR controller) or passed over a CCU
+ divider to create a signal required for the clock domain.
+
+ The CCU PLL dts-node uses the common clock bindings with no custom
+ parameters. The list of exported clocks can be found in
+ 'include/dt-bindings/clock/bt1-ccu.h'. Since CCU PLL is a part of the
+ Baikal-T1 SoC System Controller its DT node is supposed to be a child of
+ later one.
+
+properties:
+ compatible:
+ const: baikal,bt1-ccu-pll
+
+ reg:
+ maxItems: 1
+
+ "#clock-cells":
+ const: 1
+
+ clocks:
+ description: External reference clock
+ maxItems: 1
+
+ clock-names:
+ const: ref_clk
+
+unevaluatedProperties: false
+
+required:
+ - compatible
+ - "#clock-cells"
+ - clocks
+ - clock-names
+
+examples:
+ # Clock Control Unit PLL node:
+ - |
+ clock-controller@1f04d000 {
+ compatible = "baikal,bt1-ccu-pll";
+ reg = <0x1f04d000 0x028>;
+ #clock-cells = <1>;
+
+ clocks = <&clk25m>;
+ clock-names = "ref_clk";
+ };
+ # Required external oscillator:
+ - |
+ clk25m: clock-oscillator-25m {
+ compatible = "fixed-clock";
+ #clock-cells = <0>;
+ clock-frequency = <25000000>;
+ clock-output-names = "clk25m";
+ };
+...
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