|
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| -This binding is a work-in-progress, and are based on some experimental |
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| -work by benh[1]. |
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| - |
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| -Sources of clock signal can be represented by any node in the device |
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| -tree. Those nodes are designated as clock providers. Clock consumer |
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| -nodes use a phandle and clock specifier pair to connect clock provider |
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| -outputs to clock inputs. Similar to the gpio specifiers, a clock |
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| -specifier is an array of zero, one or more cells identifying the clock |
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| -output on a device. The length of a clock specifier is defined by the |
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| -value of a #clock-cells property in the clock provider node. |
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| - |
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| -[1] https://patchwork.ozlabs.org/patch/31551/ |
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| - |
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| -==Clock providers== |
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| - |
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| -Required properties: |
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| -#clock-cells: Number of cells in a clock specifier; Typically 0 for nodes |
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| - with a single clock output and 1 for nodes with multiple |
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| - clock outputs. |
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| - |
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| -Optional properties: |
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| -clock-output-names: Recommended to be a list of strings of clock output signal |
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| - names indexed by the first cell in the clock specifier. |
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| - However, the meaning of clock-output-names is domain |
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| - specific to the clock provider, and is only provided to |
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| - encourage using the same meaning for the majority of clock |
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| - providers. This format may not work for clock providers |
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| - using a complex clock specifier format. In those cases it |
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| - is recommended to omit this property and create a binding |
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| - specific names property. |
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| - |
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| - Clock consumer nodes must never directly reference |
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| - the provider's clock-output-names property. |
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| - |
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| -For example: |
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| - |
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| - oscillator { |
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| - #clock-cells = <1>; |
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| - clock-output-names = "ckil", "ckih"; |
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| - }; |
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| - |
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| -- this node defines a device with two clock outputs, the first named |
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| - "ckil" and the second named "ckih". Consumer nodes always reference |
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| - clocks by index. The names should reflect the clock output signal |
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| - names for the device. |
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| - |
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| -clock-indices: If the identifying number for the clocks in the node |
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| - is not linear from zero, then this allows the mapping of |
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| - identifiers into the clock-output-names array. |
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| - |
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| -For example, if we have two clocks <&oscillator 1> and <&oscillator 3>: |
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| - |
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| - oscillator { |
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| - compatible = "myclocktype"; |
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| - #clock-cells = <1>; |
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| - clock-indices = <1>, <3>; |
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| - clock-output-names = "clka", "clkb"; |
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| - } |
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| - |
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| - This ensures we do not have any empty strings in clock-output-names |
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| - |
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| - |
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| -==Clock consumers== |
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| - |
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| -Required properties: |
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| -clocks: List of phandle and clock specifier pairs, one pair |
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| - for each clock input to the device. Note: if the |
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| - clock provider specifies '0' for #clock-cells, then |
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| - only the phandle portion of the pair will appear. |
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| - |
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| -Optional properties: |
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| -clock-names: List of clock input name strings sorted in the same |
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| - order as the clocks property. Consumers drivers |
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| - will use clock-names to match clock input names |
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| - with clocks specifiers. |
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| -clock-ranges: Empty property indicating that child nodes can inherit named |
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| - clocks from this node. Useful for bus nodes to provide a |
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| - clock to their children. |
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| - |
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| -For example: |
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| - |
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| - device { |
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| - clocks = <&osc 1>, <&ref 0>; |
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| - clock-names = "baud", "register"; |
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| - }; |
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| - |
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| - |
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| -This represents a device with two clock inputs, named "baud" and "register". |
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| -The baud clock is connected to output 1 of the &osc device, and the register |
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| -clock is connected to output 0 of the &ref. |
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| - |
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| -==Example== |
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| - |
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| - /* external oscillator */ |
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| - osc: oscillator { |
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| - compatible = "fixed-clock"; |
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| - #clock-cells = <0>; |
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| - clock-frequency = <32678>; |
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| - clock-output-names = "osc"; |
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| - }; |
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| - |
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| - /* phase-locked-loop device, generates a higher frequency clock |
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| - * from the external oscillator reference */ |
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| - pll: pll@4c000 { |
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| - compatible = "vendor,some-pll-interface" |
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| - #clock-cells = <1>; |
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| - clocks = <&osc 0>; |
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| - clock-names = "ref"; |
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| - reg = <0x4c000 0x1000>; |
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| - clock-output-names = "pll", "pll-switched"; |
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| - }; |
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| - |
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| - /* UART, using the low frequency oscillator for the baud clock, |
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| - * and the high frequency switched PLL output for register |
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| - * clocking */ |
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| - uart@a000 { |
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| - compatible = "fsl,imx-uart"; |
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| - reg = <0xa000 0x1000>; |
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| - interrupts = <33>; |
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| - clocks = <&osc 0>, <&pll 1>; |
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| - clock-names = "baud", "register"; |
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| - }; |
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| - |
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| -This DT fragment defines three devices: an external oscillator to provide a |
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| -low-frequency reference clock, a PLL device to generate a higher frequency |
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| -clock signal, and a UART. |
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| - |
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| -* The oscillator is fixed-frequency, and provides one clock output, named "osc". |
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| -* The PLL is both a clock provider and a clock consumer. It uses the clock |
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| - signal generated by the external oscillator, and provides two output signals |
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| - ("pll" and "pll-switched"). |
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| -* The UART has its baud clock connected the external oscillator and its |
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| - register clock connected to the PLL clock (the "pll-switched" signal) |
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| - |
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| -==Assigned clock parents and rates== |
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| - |
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| -Some platforms may require initial configuration of default parent clocks |
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| -and clock frequencies. Such a configuration can be specified in a device tree |
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| -node through assigned-clocks, assigned-clock-parents and assigned-clock-rates |
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| -properties. The assigned-clock-parents property should contain a list of parent |
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| -clocks in the form of a phandle and clock specifier pair and the |
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| -assigned-clock-rates property should contain a list of frequencies in Hz. Both |
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| -these properties should correspond to the clocks listed in the assigned-clocks |
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| -property. |
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| - |
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| -To skip setting parent or rate of a clock its corresponding entry should be |
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| -set to 0, or can be omitted if it is not followed by any non-zero entry. |
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| - |
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| - uart@a000 { |
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| - compatible = "fsl,imx-uart"; |
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| - reg = <0xa000 0x1000>; |
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| - ... |
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| - clocks = <&osc 0>, <&pll 1>; |
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| - clock-names = "baud", "register"; |
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| - |
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| - assigned-clocks = <&clkcon 0>, <&pll 2>; |
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| - assigned-clock-parents = <&pll 2>; |
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| - assigned-clock-rates = <0>, <460800>; |
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| - }; |
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| - |
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| -In this example the <&pll 2> clock is set as parent of clock <&clkcon 0> and |
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| -the <&pll 2> clock is assigned a frequency value of 460800 Hz. |
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| - |
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| -Configuring a clock's parent and rate through the device node that consumes |
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| -the clock can be done only for clocks that have a single user. Specifying |
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| -conflicting parent or rate configuration in multiple consumer nodes for |
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| -a shared clock is forbidden. |
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| - |
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| -Configuration of common clocks, which affect multiple consumer devices can |
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| -be similarly specified in the clock provider node. |
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| - |
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| -==Protected clocks== |
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| - |
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| -Some platforms or firmwares may not fully expose all the clocks to the OS, such |
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| -as in situations where those clks are used by drivers running in ARM secure |
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| -execution levels. Such a configuration can be specified in device tree with the |
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| -protected-clocks property in the form of a clock specifier list. This property should |
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| -only be specified in the node that is providing the clocks being protected: |
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| - |
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| - clock-controller@a000f000 { |
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| - compatible = "vendor,clk95; |
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| - reg = <0xa000f000 0x1000> |
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| - #clocks-cells = <1>; |
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| - ... |
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| - protected-clocks = <UART3_CLK>, <SPI5_CLK>; |
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| - }; |
| 1 | +This file has moved to the clock binding schema: |
| 2 | +https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/clock/clock.yaml |
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