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diff --git a/Documentation/devicetree/bindings/clock/baikal,bt1-ccu-pll.yaml b/Documentation/devicetree/bindings/clock/baikal,bt1-ccu-pll.yaml new file mode 100644 index 000000000000..97131bfa6f87 --- /dev/null +++ b/Documentation/devicetree/bindings/clock/baikal,bt1-ccu-pll.yaml @@ -0,0 +1,131 @@ +# 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"; + }; +... |