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Based on work 1st by Ben Herrenschmidt and Jeremy Kerr, then by Grant
Likely, this patch adds support to clk_get to allow drivers to retrieve
clock data from the device tree.
Platforms scan for clocks in DT with of_clk_init and a match table, and
the register a provider through of_clk_add_provider. The provider's
clk_src_get function will be called when a device references the
provider's OF node for a clock reference.
v6 (Rob Herring):
- Return error values instead of NULL to match clock framework
expectations
v5 (Rob Herring):
- Move from drivers/of into common clock subsystem
- Squashed "dt/clock: add a simple provider get function" and
"dt/clock: add function to get parent clock name"
- Rebase to 3.4-rc1
- Drop CONFIG_OF_CLOCK and just use CONFIG_OF
- Add missing EXPORT_SYMBOL to various functions
- s/clock-output-name/clock-output-names/
- Define that fixed-clock binding is a single output
v4 (Rob Herring):
- Rework for common clk subsystem
- Add of_clk_get_parent_name function
v3: - Clarified documentation
v2: - fixed errant ';' causing compile error
- Editorial fixes from Shawn Guo
- merged in adding lookup to clkdev
- changed property names to match established convention. After
working with the binding a bit it really made more sense to follow the
lead of 'reg', 'gpios' and 'interrupts' by making the input simply
'clocks' & 'clock-names' instead of 'clock-input-*', and to only use
clock-output* for the producer nodes. (Sorry Shawn, this will mean
you need to change some code, but it should be trivial)
- Add ability to inherit clocks from parent nodes by using an empty
'clock-ranges' property. Useful for busses. I could use some feedback
on the new property name, 'clock-ranges' doesn't feel right to me.
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Reviewed-by: Shawn Guo <shawn.guo@freescale.com>
Cc: Sascha Hauer <kernel@pengutronix.de>
Signed-off-by: Mike Turquette <mturquette@linaro.org>
118 lines
4.2 KiB
Plaintext
118 lines
4.2 KiB
Plaintext
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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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 one more 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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[1] http://patchwork.ozlabs.org/patch/31551/
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==Clock providers==
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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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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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Clock consumer nodes must never directly reference
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the provider's clock-output-names property.
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For example:
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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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- 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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==Clock consumers==
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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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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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For example:
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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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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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==Example==
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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 = <1>;
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clock-frequency = <32678>;
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clock-output-names = "osc";
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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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/* 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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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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* 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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