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From:   Mike Looijmans <mike.looijmans@topic.nl>
To:     devicetree@vger.kernel.org, linux-clk@vger.kernel.org
CC:     Mike Looijmans <mike.looijmans@topic.nl>,
        Conor Dooley <conor+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Michael Turquette <mturquette@baylibre.com>,
        Rob Herring <robh+dt@kernel.org>,
        Stephen Boyd <sboyd@kernel.org>, linux-kernel@vger.kernel.org
Subject: [PATCH v2 1/2] dt-bindings: clock: Add nvmem-clock
Date:   Fri, 26 May 2023 16:38:06 +0200
Message-ID: <20230526143807.10164-1-mike.looijmans@topic.nl>
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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@topic.nl>

---

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.yam=
l

diff --git a/Documentation/devicetree/bindings/clock/nvmem-clock.yaml b/Doc=
umentation/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@topic.nl>
+
+description:
+  Provides a clock rate from NVMEM. Typical usage is that the factory plac=
es a
+  crystal on the board and writes the rate into an EEPROM or EFUSE. If som=
e 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 pr=
ovider
+      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 provid=
ing
+      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 =3D "nvmem-clock";
+      #clock-cells =3D <0>;
+      nvmem-cells =3D <&efuse_xtal_freq>;
+      nvmem-cell-names =3D "clock-frequency";
+    };
+...
--=20
2.17.1


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