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# 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";
};
...
|
