dt-bindings: clk: Add Baikal-T1 CCU Dividers binding

After being gained by the CCU PLLs the signals must be transformed to
be suitable for the clock-consumers. This is done by a set of dividers
embedded into the CCU. A first block of dividers is used to create
reference clocks for AXI-bus of high-speed peripheral IP-cores of the
chip. The second block dividers alter the PLLs output signals to be then
consumed by SoC peripheral devices. Both block DT nodes are ordinary
clock-providers with standard set of properties supported. But in addition
to that each clock provider can be used to reset the corresponding clock
domain. This makes the AXI-bus and System Devices CCU DT nodes to be also
reset-providers.

Signed-off-by: Serge Semin <[e-mail]>
Cc: Alexey Malahov <[e-mail]>
Cc: Arnd Bergmann <[e-mail]>
Cc: [e-mail]
Link: https://lore.kernel.org/r/[e-mail]
Reviewed-by: Rob Herring <[e-mail]>
Signed-off-by: Stephen Boyd <[e-mail]>

Documentation/devicetree/bindings/clock/baikal,bt1-ccu-div.yaml

···
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+# Copyright (C) 2020 BAIKAL ELECTRONICS, JSC
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/clock/baikal,bt1-ccu-div.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Baikal-T1 Clock Control Unit Dividers
+
+maintainers:
+  - Serge Semin <[e-mail]>
+
+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 an embedded into CCU PLLs and gateable/non-gateable dividers. The
+  later ones are described in this binding. Each clock domain can be also
+  individually reset by using the domain clocks divider configuration
+  registers. Baikal-T1 CCU is 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).
+  3) AXI-bus clock dividers (AXI) - described in this binding file.
+  4) System devices reference clock dividers (SYS) - described in this binding
+     file.
+  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 sub-block is represented as a separate DT 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. Some of PLLs CLKOUT are
+  then passed over CCU dividers to create signals required for the target clock
+  domain (like AXI-bus or System Device consumers). The dividers have the
+  following structure:
+
+          +--------------+
+  CLKIN --|->+----+ 1|\  |
+  SETCLK--|--|/DIV|->| | |
+  CLKDIV--|--|    |  | |-|->CLKLOUT
+  LOCK----|--+----+  | | |
+          |          |/  |
+          |           |  |
+  EN------|-----------+  |
+  RST-----|--------------|->RSTOUT
+          +--------------+
+
+  where CLKIN is the reference clock coming either from CCU PLLs or from an
+  external clock oscillator, SETCLK - a command to update the output clock in
+  accordance with a set divider, CLKDIV - clocks divider, LOCK - a signal of
+  the output clock stabilization, EN - enable/disable the divider block,
+  RST/RSTOUT - reset clocks domain signal. Depending on the consumer IP-core
+  peculiarities the dividers may lack of some functionality depicted on the
+  figure above (like EN, CLKDIV/LOCK/SETCLK). In this case the corresponding
+  clock provider just doesn't expose either switching functions, or the rate
+  configuration, or both of them.
+
+  The clock dividers, which output clock is then consumed by the SoC individual
+  devices, are united into a single clocks provider called System Devices CCU.
+  Similarly the dividers with output clocks utilized as AXI-bus reference clocks
+  are called AXI-bus CCU. Both of them use the common clock bindings with no
+  custom properties. The list of exported clocks and reset signals can be found
+  in the files: 'include/dt-bindings/clock/bt1-ccu.h' and
+  'include/dt-bindings/reset/bt1-ccu.h'. Since System Devices and AXI-bus CCU
+  are a part of the Baikal-T1 SoC System Controller their DT nodes are supposed
+  to be a children of later one.
+
+if:
+  properties:
+    compatible:
+      contains:
+        const: baikal,bt1-ccu-axi
+
+then:
+  properties:
+    clocks:
+      items:
+        - description: CCU SATA PLL output clock
+        - description: CCU PCIe PLL output clock
+        - description: CCU Ethernet PLL output clock
+
+    clock-names:
+      items:
+        - const: sata_clk
+        - const: pcie_clk
+        - const: eth_clk
+
+else:
+  properties:
+    clocks:
+      items:
+        - description: External reference clock
+        - description: CCU SATA PLL output clock
+        - description: CCU PCIe PLL output clock
+        - description: CCU Ethernet PLL output clock
+
+    clock-names:
+      items:
+        - const: ref_clk
+        - const: sata_clk
+        - const: pcie_clk
+        - const: eth_clk
+
+properties:
+  compatible:
+    enum:
+      - baikal,bt1-ccu-axi
+      - baikal,bt1-ccu-sys
+
+  reg:
+    maxItems: 1
+
+  "#clock-cells":
+    const: 1
+
+  "#reset-cells":
+    const: 1
+
+unevaluatedProperties: false
+
+required:
+  - compatible
+  - "#clock-cells"
+  - clocks
+  - clock-names
+
+examples:
+  # AXI-bus Clock Control Unit node:
+  - |
+    #include <dt-bindings/clock/bt1-ccu.h>
+
+    clock-controller@1f04d030 {
+      compatible = "baikal,bt1-ccu-axi";
+      reg = <0x1f04d030 0x030>;
+      #clock-cells = <1>;
+      #reset-cells = <1>;
+
+      clocks = <&ccu_pll CCU_SATA_PLL>,
+               <&ccu_pll CCU_PCIE_PLL>,
+               <&ccu_pll CCU_ETH_PLL>;
+      clock-names = "sata_clk", "pcie_clk", "eth_clk";
+    };
+  # System Devices Clock Control Unit node:
+  - |
+    #include <dt-bindings/clock/bt1-ccu.h>
+
+    clock-controller@1f04d060 {
+      compatible = "baikal,bt1-ccu-sys";
+      reg = <0x1f04d060 0x0a0>;
+      #clock-cells = <1>;
+      #reset-cells = <1>;
+
+      clocks = <&clk25m>,
+               <&ccu_pll CCU_SATA_PLL>,
+               <&ccu_pll CCU_PCIE_PLL>,
+               <&ccu_pll CCU_ETH_PLL>;
+      clock-names = "ref_clk", "sata_clk", "pcie_clk",
+                    "eth_clk";
+    };
+  # Required Clock Control Unit PLL node:
+  - |
+    ccu_pll: clock-controller@1f04d000 {
+      compatible = "baikal,bt1-ccu-pll";
+      reg = <0x1f04d000 0x028>;
+      #clock-cells = <1>;
+
+      clocks = <&clk25m>;
+      clock-names = "ref_clk";
+    };
+...

include/dt-bindings/clock/bt1-ccu.h

···
 #define CCU_PCIE_PLL			3
 #define CCU_ETH_PLL			4
 
+#define CCU_AXI_MAIN_CLK		0
+#define CCU_AXI_DDR_CLK			1
+#define CCU_AXI_SATA_CLK		2
+#define CCU_AXI_GMAC0_CLK		3
+#define CCU_AXI_GMAC1_CLK		4
+#define CCU_AXI_XGMAC_CLK		5
+#define CCU_AXI_PCIE_M_CLK		6
+#define CCU_AXI_PCIE_S_CLK		7
+#define CCU_AXI_USB_CLK			8
+#define CCU_AXI_HWA_CLK			9
+#define CCU_AXI_SRAM_CLK		10
+
+#define CCU_SYS_SATA_REF_CLK		0
+#define CCU_SYS_APB_CLK			1
+#define CCU_SYS_GMAC0_TX_CLK		2
+#define CCU_SYS_GMAC0_PTP_CLK		3
+#define CCU_SYS_GMAC1_TX_CLK		4
+#define CCU_SYS_GMAC1_PTP_CLK		5
+#define CCU_SYS_XGMAC_REF_CLK		6
+#define CCU_SYS_XGMAC_PTP_CLK		7
+#define CCU_SYS_USB_CLK			8
+#define CCU_SYS_PVT_CLK			9
+#define CCU_SYS_HWA_CLK			10
+#define CCU_SYS_UART_CLK		11
+#define CCU_SYS_I2C1_CLK		12
+#define CCU_SYS_I2C2_CLK		13
+#define CCU_SYS_GPIO_CLK		14
+#define CCU_SYS_TIMER0_CLK		15
+#define CCU_SYS_TIMER1_CLK		16
+#define CCU_SYS_TIMER2_CLK		17
+#define CCU_SYS_WDT_CLK			18
+
 #endif /* __DT_BINDINGS_CLOCK_BT1_CCU_H */

include/dt-bindings/reset/bt1-ccu.h

···
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2020 BAIKAL ELECTRONICS, JSC
+ *
+ * Baikal-T1 CCU reset indices
+ */
+#ifndef __DT_BINDINGS_RESET_BT1_CCU_H
+#define __DT_BINDINGS_RESET_BT1_CCU_H
+
+#define CCU_AXI_MAIN_RST		0
+#define CCU_AXI_DDR_RST			1
+#define CCU_AXI_SATA_RST		2
+#define CCU_AXI_GMAC0_RST		3
+#define CCU_AXI_GMAC1_RST		4
+#define CCU_AXI_XGMAC_RST		5
+#define CCU_AXI_PCIE_M_RST		6
+#define CCU_AXI_PCIE_S_RST		7
+#define CCU_AXI_USB_RST			8
+#define CCU_AXI_HWA_RST			9
+#define CCU_AXI_SRAM_RST		10
+
+#define CCU_SYS_SATA_REF_RST		0
+#define CCU_SYS_APB_RST			1
+
+#endif /* __DT_BINDINGS_RESET_BT1_CCU_H */