Add bindings for a fixed-rate clock that retrieves its rate from an NVMEM provider. This allows to store clock settings in EEPROM or EFUSE or similar device. Component shortages lead to boards being shipped with different clock crystals, based on what was available at the time. The clock frequency was written to EEPROM at production time. Systems can adapt to a wide range of input frequencies using the clock framework, but this required us to patch the devicetree at runtime or use some custom driver. This provides a more generic solution. Signed-off-by: Mike Looijmans <mike.looijmans@xxxxxxxx> --- Changes in v2: Changed "fixed-clock" into "nvmem-clock" in dts example Add minItems:1 to nvmem-cell-names .../bindings/clock/nvmem-clock.yaml | 63 +++++++++++++++++++ 1 file changed, 63 insertions(+) create mode 100644 Documentation/devicetree/bindings/clock/nvmem-clock.yaml diff --git a/Documentation/devicetree/bindings/clock/nvmem-clock.yaml b/Documentation/devicetree/bindings/clock/nvmem-clock.yaml new file mode 100644 index 000000000000..af96a5e9372d --- /dev/null +++ b/Documentation/devicetree/bindings/clock/nvmem-clock.yaml @@ -0,0 +1,63 @@ +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) +%YAML 1.2 +--- +$id: http://devicetree.org/schemas/clock/nvmem-clock.yaml# +$schema: http://devicetree.org/meta-schemas/core.yaml# + +title: Simple fixed-rate clock source from NVMEM + +maintainers: + - Mike Looijmans <mike.looijmans@xxxxxxxx> + +description: + Provides a clock rate from NVMEM. Typical usage is that the factory places a + crystal on the board and writes the rate into an EEPROM or EFUSE. If some math + is required, one can add a fixed-factor clock using this clock as input. + +properties: + compatible: + const: nvmem-clock + + "#clock-cells": + const: 0 + + nvmem-cells: + minItems: 1 + maxItems: 2 + description: + Reads clock-frequency and optionally clock-accuracy from an NVMEM provider + in binary native integer format. The size of the NVMEM cell can be 1, 2, 4 + or 8 bytes. + + nvmem-cell-names: + minItems: 1 + items: + - const: clock-frequency + - const: clock-accuracy + + clock-accuracy: + $ref: /schemas/types.yaml#/definitions/uint32 + description: + accuracy of clock in ppb (parts per billion). Alternative for providing + this through nvmem, the nvmem provided value takes precedence. + + clock-output-names: + maxItems: 1 + +required: + - compatible + - "#clock-cells" + - nvmem-cells + - nvmem-cell-names + +additionalProperties: false + +examples: + - | + xtal { + compatible = "nvmem-clock"; + #clock-cells = <0>; + nvmem-cells = <&efuse_xtal_freq>; + nvmem-cell-names = "clock-frequency"; + }; +... -- 2.17.1 Met vriendelijke groet / kind regards, Mike Looijmans System Expert TOPIC Embedded Products B.V. Materiaalweg 4, 5681 RJ Best The Netherlands T: +31 (0) 499 33 69 69 E: mike.looijmans@xxxxxxxxxxxxxxxxx W: www.topic.nl Please consider the environment before printing this e-mail
