linux-kernel - [PATCH v2 1/2] dt-bindings: clk: fixed-mmio-clock: Add optional ready reg

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Message-ID: <20250528140917.876453-2-edgar.iglesias@gmail.com>
Date: Wed, 28 May 2025 16:09:16 +0200
From: "Edgar E. Iglesias" <edgar.iglesias@...il.com>
To: mturquette@...libre.com,
	sboyd@...nel.org,
	robh@...nel.org,
	krzk+dt@...nel.org,
	conor+dt@...nel.org,
	jank@...ence.com
Cc: edgar.iglesias@....com,
	linux-clk@...r.kernel.org,
	devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2 1/2] dt-bindings: clk: fixed-mmio-clock: Add optional ready reg

From: "Edgar E. Iglesias" <edgar.iglesias@....com>

Add an optional ready register and properties describing bitfields
that signal when the clock is ready. This can for example be useful
to describe PLL lock bits.

Signed-off-by: Edgar E. Iglesias <edgar.iglesias@....com>
---
 .../bindings/clock/fixed-mmio-clock.yaml      | 37 ++++++++++++++++++-
 1 file changed, 36 insertions(+), 1 deletion(-)

diff --git a/Documentation/devicetree/bindings/clock/fixed-mmio-clock.yaml b/Documentation/devicetree/bindings/clock/fixed-mmio-clock.yaml
index e22fc272d023..57419b4de343 100644
--- a/Documentation/devicetree/bindings/clock/fixed-mmio-clock.yaml
+++ b/Documentation/devicetree/bindings/clock/fixed-mmio-clock.yaml
@@ -10,6 +10,11 @@ description:
   This binding describes a fixed-rate clock for which the frequency can
   be read from a single 32-bit memory mapped I/O register.
 
+  An optional ready register can be specified in a second reg entry.
+  The ready register will be polled until it signals ready prior to reading
+  the fixed rate. This is useful for example to optionally wait for a PLL
+  to lock.
+
   It was designed for test systems, like FPGA, not for complete,
   finished SoCs.
 
@@ -21,7 +26,10 @@ properties:
     const: fixed-mmio-clock
 
   reg:
-    maxItems: 1
+    minItems: 1
+    items:
+      - description: Fixed rate register
+      - description: Optional clock ready register
 
   "#clock-cells":
     const: 0
@@ -29,6 +37,24 @@ properties:
   clock-output-names:
     maxItems: 1
 
+  ready-timeout-us:
+    description:
+      Optional timeout in micro-seconds when polling for clock readiness.
+      0 means no timeout.
+    default: 0
+
+  ready-mask:
+    description:
+      Optional mask to apply when reading the ready register.
+    $ref: /schemas/types.yaml#/definitions/uint32
+    default: 0xffffffff
+
+  ready-value:
+    description:
+      When a ready register is specified in reg, poll the ready reg until
+      ready-reg & ready-mask == ready-value.
+    $ref: /schemas/types.yaml#/definitions/uint32
+
 required:
   - compatible
   - reg
@@ -44,4 +70,13 @@ examples:
       reg = <0xfd020004 0x4>;
       clock-output-names = "sysclk";
     };
+  - |
+    clock@...40000 {
+      compatible = "fixed-mmio-clock";
+      #clock-cells = <0>;
+      reg = <0xfd040000 0x4 0xfd040004 0x4>;
+      ready-mask = <1>;
+      ready-value = <1>;
+      clock-output-names = "pclk";
+    };
 ...
-- 
2.43.0