xref: /linux/Documentation/devicetree/bindings/clock/baikal,bt1-ccu-pll.yaml (revision 249ebf3f65f8530beb2cbfb91bff1d83ba88d23c) 
1# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
2# Copyright (C) 2020 BAIKAL ELECTRONICS, JSC
3%YAML 1.2
4---
5$id: http://devicetree.org/schemas/clock/baikal,bt1-ccu-pll.yaml#
6$schema: http://devicetree.org/meta-schemas/core.yaml#
7
8title: Baikal-T1 Clock Control Unit PLL
9
10maintainers:
11  - Serge Semin <fancer.lancer@gmail.com>
12
13description: |
14  Clocks Control Unit is the core of Baikal-T1 SoC System Controller
15  responsible for the chip subsystems clocking and resetting. The CCU is
16  connected with an external fixed rate oscillator, which signal is transformed
17  into clocks of various frequencies and then propagated to either individual
18  IP-blocks or to groups of blocks (clock domains). The transformation is done
19  by means of PLLs and gateable/non-gateable dividers embedded into the CCU.
20  It's logically divided into the next components:
21  1) External oscillator (normally XTAL's 25 MHz crystal oscillator, but
22     in general can provide any frequency supported by the CCU PLLs).
23  2) PLLs clocks generators (PLLs) - described in this binding file.
24  3) AXI-bus clock dividers (AXI).
25  4) System devices reference clock dividers (SYS).
26  which are connected with each other as shown on the next figure:
27
28          +---------------+
29          | Baikal-T1 CCU |
30          |   +----+------|- MIPS P5600 cores
31          | +-|PLLs|------|- DDR controller
32          | | +----+      |
33  +----+  | |  |  |       |
34  |XTAL|--|-+  |  | +---+-|
35  +----+  | |  |  +-|AXI|-|- AXI-bus
36          | |  |    +---+-|
37          | |  |          |
38          | |  +----+---+-|- APB-bus
39          | +-------|SYS|-|- Low-speed Devices
40          |         +---+-|- High-speed Devices
41          +---------------+
42
43  Each CCU sub-block is represented as a separate dts-node and has an
44  individual driver to be bound with.
45
46  In order to create signals of wide range frequencies the external oscillator
47  output is primarily connected to a set of CCU PLLs. There are five PLLs
48  to create a clock for the MIPS P5600 cores, the embedded DDR controller,
49  SATA, Ethernet and PCIe domains. The last three domains though named by the
50  biggest system interfaces in fact include nearly all of the rest SoC
51  peripherals. Each of the PLLs is based on True Circuits TSMC CLN28HPM core
52  with an interface wrapper (so called safe PLL' clocks switcher) to simplify
53  the PLL configuration procedure. The PLLs work as depicted on the next
54  diagram:
55
56      +--------------------------+
57      |                          |
58      +-->+---+    +---+   +---+ |  +---+   0|\
59  CLKF--->|/NF|--->|PFD|...|VCO|-+->|/OD|--->| |
60          +---+ +->+---+   +---+ /->+---+    | |--->CLKOUT
61  CLKOD---------C----------------+          1| |
62       +--------C--------------------------->|/
63       |        |                             ^
64  Rclk-+->+---+ |                             |
65  CLKR--->|/NR|-+                             |
66          +---+                               |
67  BYPASS--------------------------------------+
68  BWADJ--->
69
70  where Rclk is the reference clock coming  from XTAL, NR - reference clock
71  divider, NF - PLL clock multiplier, OD - VCO output clock divider, CLKOUT -
72  output clock, BWADJ is the PLL bandwidth adjustment parameter. At this moment
73  the binding supports the PLL dividers configuration in accordance with a
74  requested rate, while bypassing and bandwidth adjustment settings can be
75  added in future if it gets to be necessary.
76
77  The PLLs CLKOUT is then either directly connected with the corresponding
78  clocks consumer (like P5600 cores or DDR controller) or passed over a CCU
79  divider to create a signal required for the clock domain.
80
81  The CCU PLL dts-node uses the common clock bindings with no custom
82  parameters. The list of exported clocks can be found in
83  'include/dt-bindings/clock/bt1-ccu.h'. Since CCU PLL is a part of the
84  Baikal-T1 SoC System Controller its DT node is supposed to be a child of
85  later one.
86
87properties:
88  compatible:
89    const: baikal,bt1-ccu-pll
90
91  reg:
92    maxItems: 1
93
94  "#clock-cells":
95    const: 1
96
97  clocks:
98    description: External reference clock
99    maxItems: 1
100
101  clock-names:
102    const: ref_clk
103
104additionalProperties: false
105
106required:
107  - compatible
108  - "#clock-cells"
109  - clocks
110  - clock-names
111
112examples:
113  # Clock Control Unit PLL node:
114  - |
115    clock-controller@1f04d000 {
116      compatible = "baikal,bt1-ccu-pll";
117      reg = <0x1f04d000 0x028>;
118      #clock-cells = <1>;
119
120      clocks = <&clk25m>;
121      clock-names = "ref_clk";
122    };
123  # Required external oscillator:
124  - |
125    clk25m: clock-oscillator-25m {
126      compatible = "fixed-clock";
127      #clock-cells = <0>;
128      clock-frequency = <25000000>;
129      clock-output-names = "clk25m";
130    };
131...
132