linux-kernel - [PATCH v4 1/2] dt-bindings: clock: fixed-clock: Add nvmem support

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Message-ID: <20230605140149.16841-1-mike.looijmans@topic.nl>
Date:   Mon, 5 Jun 2023 16:01:48 +0200
From:   Mike Looijmans <mike.looijmans@...ic.nl>
To:     devicetree@...r.kernel.org, linux-clk@...r.kernel.org
CC:     Mike Looijmans <mike.looijmans@...ic.nl>,
        Conor Dooley <conor+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Michael Turquette <mturquette@...libre.com>,
        Rob Herring <robh+dt@...nel.org>,
        Stephen Boyd <sboyd@...nel.org>, linux-kernel@...r.kernel.org
Subject: [PATCH v4 1/2] dt-bindings: clock: fixed-clock: Add nvmem support

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@...ic.nl>

---

Changes in v4:
Use proper "if" block and add example dts

Changes in v3:
Modify fixed-clock instead of introducing nvmem-clock

Changes in v2:
Changed "fixed-clock" into "nvmem-clock" in dts example
Add minItems:1 to nvmem-cell-names

 .../bindings/clock/fixed-clock.yaml           | 42 ++++++++++++++++++-
 1 file changed, 41 insertions(+), 1 deletion(-)

diff --git a/Documentation/devicetree/bindings/clock/fixed-clock.yaml b/Documentation/devicetree/bindings/clock/fixed-clock.yaml
index b0a4fb8256e2..71a5791da438 100644
--- a/Documentation/devicetree/bindings/clock/fixed-clock.yaml
+++ b/Documentation/devicetree/bindings/clock/fixed-clock.yaml
@@ -12,7 +12,9 @@ maintainers:
 
 properties:
   compatible:
-    const: fixed-clock
+    enum:
+      - fixed-clock
+      - fixed-clock-nvmem
 
   "#clock-cells":
     const: 0
@@ -26,11 +28,41 @@ properties:
   clock-output-names:
     maxItems: 1
 
+  nvmem-cells:
+    minItems: 1
+    maxItems: 2
+    description:
+      Reads clock-frequency and/or 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. If the contents of the nvmem are all zeroes or all 0xff, the
+      value reverts to the one given in the property.
+
+  nvmem-cell-names:
+    minItems: 1
+    items:
+      - const: clock-frequency
+      - const: clock-accuracy
+
 required:
   - compatible
   - "#clock-cells"
   - clock-frequency
 
+allOf:
+  - if:
+      properties:
+        compatible:
+          contains:
+            const: fixed-clock-nvmem
+    then:
+      required:
+        - nvmem-cells
+        - nvmem-cell-names
+    else:
+      properties:
+        nvmem-cells: false
+        nvmem-cell-names: false
+
 additionalProperties: false
 
 examples:
@@ -41,4 +73,12 @@ examples:
       clock-frequency = <1000000000>;
       clock-accuracy = <100>;
     };
+  - |
+    clock {
+      compatible = "fixed-clock-nvmem";
+      #clock-cells = <0>;
+      clock-frequency = <48000000>;
+      nvmem-cells = <&efuse_xtal_freq>;
+      nvmem-cell-names = "clock-frequency";
+    };
 ...
-- 
2.17.1


Met vriendelijke groet / kind regards,

Mike Looijmans
System Expert


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