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diff --git a/Documentation/devicetree/bindings/clock/clock-bindings.txt b/Documentation/devicetree/bindings/clock/clock-bindings.txt new file mode 100644 index 000000000..f2ea53832 --- /dev/null +++ b/Documentation/devicetree/bindings/clock/clock-bindings.txt @@ -0,0 +1,186 @@ +This binding is a work-in-progress, and are based on some experimental +work by benh[1]. + +Sources of clock signal can be represented by any node in the device +tree. Those nodes are designated as clock providers. Clock consumer +nodes use a phandle and clock specifier pair to connect clock provider +outputs to clock inputs. Similar to the gpio specifiers, a clock +specifier is an array of zero, one or more cells identifying the clock +output on a device. The length of a clock specifier is defined by the +value of a #clock-cells property in the clock provider node. + +[1] https://patchwork.ozlabs.org/patch/31551/ + +==Clock providers== + +Required properties: +#clock-cells: Number of cells in a clock specifier; Typically 0 for nodes + with a single clock output and 1 for nodes with multiple + clock outputs. + +Optional properties: +clock-output-names: Recommended to be a list of strings of clock output signal + names indexed by the first cell in the clock specifier. + However, the meaning of clock-output-names is domain + specific to the clock provider, and is only provided to + encourage using the same meaning for the majority of clock + providers. This format may not work for clock providers + using a complex clock specifier format. In those cases it + is recommended to omit this property and create a binding + specific names property. + + Clock consumer nodes must never directly reference + the provider's clock-output-names property. + +For example: + + oscillator { + #clock-cells = <1>; + clock-output-names = "ckil", "ckih"; + }; + +- this node defines a device with two clock outputs, the first named + "ckil" and the second named "ckih". Consumer nodes always reference + clocks by index. The names should reflect the clock output signal + names for the device. + +clock-indices: If the identifying number for the clocks in the node + is not linear from zero, then this allows the mapping of + identifiers into the clock-output-names array. + +For example, if we have two clocks <&oscillator 1> and <&oscillator 3>: + + oscillator { + compatible = "myclocktype"; + #clock-cells = <1>; + clock-indices = <1>, <3>; + clock-output-names = "clka", "clkb"; + } + + This ensures we do not have any empty strings in clock-output-names + + +==Clock consumers== + +Required properties: +clocks: List of phandle and clock specifier pairs, one pair + for each clock input to the device. Note: if the + clock provider specifies '0' for #clock-cells, then + only the phandle portion of the pair will appear. + +Optional properties: +clock-names: List of clock input name strings sorted in the same + order as the clocks property. Consumers drivers + will use clock-names to match clock input names + with clocks specifiers. +clock-ranges: Empty property indicating that child nodes can inherit named + clocks from this node. Useful for bus nodes to provide a + clock to their children. + +For example: + + device { + clocks = <&osc 1>, <&ref 0>; + clock-names = "baud", "register"; + }; + + +This represents a device with two clock inputs, named "baud" and "register". +The baud clock is connected to output 1 of the &osc device, and the register +clock is connected to output 0 of the &ref. + +==Example== + + /* external oscillator */ + osc: oscillator { + compatible = "fixed-clock"; + #clock-cells = <0>; + clock-frequency = <32678>; + clock-output-names = "osc"; + }; + + /* phase-locked-loop device, generates a higher frequency clock + * from the external oscillator reference */ + pll: pll@4c000 { + compatible = "vendor,some-pll-interface" + #clock-cells = <1>; + clocks = <&osc 0>; + clock-names = "ref"; + reg = <0x4c000 0x1000>; + clock-output-names = "pll", "pll-switched"; + }; + + /* UART, using the low frequency oscillator for the baud clock, + * and the high frequency switched PLL output for register + * clocking */ + uart@a000 { + compatible = "fsl,imx-uart"; + reg = <0xa000 0x1000>; + interrupts = <33>; + clocks = <&osc 0>, <&pll 1>; + clock-names = "baud", "register"; + }; + +This DT fragment defines three devices: an external oscillator to provide a +low-frequency reference clock, a PLL device to generate a higher frequency +clock signal, and a UART. + +* The oscillator is fixed-frequency, and provides one clock output, named "osc". +* The PLL is both a clock provider and a clock consumer. It uses the clock + signal generated by the external oscillator, and provides two output signals + ("pll" and "pll-switched"). +* The UART has its baud clock connected the external oscillator and its + register clock connected to the PLL clock (the "pll-switched" signal) + +==Assigned clock parents and rates== + +Some platforms may require initial configuration of default parent clocks +and clock frequencies. Such a configuration can be specified in a device tree +node through assigned-clocks, assigned-clock-parents and assigned-clock-rates +properties. The assigned-clock-parents property should contain a list of parent +clocks in the form of a phandle and clock specifier pair and the +assigned-clock-rates property should contain a list of frequencies in Hz. Both +these properties should correspond to the clocks listed in the assigned-clocks +property. + +To skip setting parent or rate of a clock its corresponding entry should be +set to 0, or can be omitted if it is not followed by any non-zero entry. + + uart@a000 { + compatible = "fsl,imx-uart"; + reg = <0xa000 0x1000>; + ... + clocks = <&osc 0>, <&pll 1>; + clock-names = "baud", "register"; + + assigned-clocks = <&clkcon 0>, <&pll 2>; + assigned-clock-parents = <&pll 2>; + assigned-clock-rates = <0>, <460800>; + }; + +In this example the <&pll 2> clock is set as parent of clock <&clkcon 0> and +the <&pll 2> clock is assigned a frequency value of 460800 Hz. + +Configuring a clock's parent and rate through the device node that consumes +the clock can be done only for clocks that have a single user. Specifying +conflicting parent or rate configuration in multiple consumer nodes for +a shared clock is forbidden. + +Configuration of common clocks, which affect multiple consumer devices can +be similarly specified in the clock provider node. + +==Protected clocks== + +Some platforms or firmwares may not fully expose all the clocks to the OS, such +as in situations where those clks are used by drivers running in ARM secure +execution levels. Such a configuration can be specified in device tree with the +protected-clocks property in the form of a clock specifier list. This property should +only be specified in the node that is providing the clocks being protected: + + clock-controller@a000f000 { + compatible = "vendor,clk95; + reg = <0xa000f000 0x1000> + #clocks-cells = <1>; + ... + protected-clocks = <UART3_CLK>, <SPI5_CLK>; + }; |