linux-kernel - [PATCH V4 1/2] dt-bindings: nvmem: mmio: new binding for MMIO accessible NVMEM devices

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Message-Id: <20230228072936.1108-2-zajec5@gmail.com>
Date:   Tue, 28 Feb 2023 08:29:35 +0100
From:   Rafał Miłecki <zajec5@...il.com>
To:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>
Cc:     Matthias Brugger <matthias.bgg@...il.com>,
        Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Rafał Miłecki <rafal@...ecki.pl>,
        Rob Herring <robh@...nel.org>
Subject: [PATCH V4 1/2] dt-bindings: nvmem: mmio: new binding for MMIO accessible NVMEM devices

From: Rafał Miłecki <rafal@...ecki.pl>

Content of some NVMEM devices can be read using MMIO. Some of them
(probably very few though) may be also programmable that way. Add
generic binding to allow describing such hardware.

This *doesn't* apply to any more complicated devices that need more
complex interface e.g. for writing. While such devices could be
supported for reading purposes by the same driver - they should get
their own binding.

This binding will gain even more usability once we fully support NVMEM
layouts (describing content of NVMEM devices in an independent way).

Signed-off-by: Rafał Miłecki <rafal@...ecki.pl>
Reviewed-by: Rob Herring <robh@...nel.org>
---
V3: Make it clear this binding should NOT be used for more complex devices
---
 .../devicetree/bindings/nvmem/mmio.yaml       | 50 +++++++++++++++++++
 1 file changed, 50 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/nvmem/mmio.yaml

diff --git a/Documentation/devicetree/bindings/nvmem/mmio.yaml b/Documentation/devicetree/bindings/nvmem/mmio.yaml
new file mode 100644
index 000000000000..9ca96b7a4856
--- /dev/null
+++ b/Documentation/devicetree/bindings/nvmem/mmio.yaml
@@ -0,0 +1,50 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/nvmem/mmio.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: MMIO access based NVMEM
+
+description: |
+  This binding describes simple NVMEM devices with content that can be accessed
+  using MMIO (memory-mapped I/O access).
+
+  More complex devices that support any other access than a simple memory
+  mapping should use a custom binding. In such cases this binding's compatible
+  should NOT be used even as a fallback.
+
+  This binding is designed to describe just an NVMEM content access method. The
+  way of handling actual content should be described independently (on top of
+  this binding).
+
+maintainers:
+  - Rafał Miłecki <rafal@...ecki.pl>
+
+allOf:
+  - $ref: nvmem.yaml#
+
+properties:
+  compatible:
+    const: mmio-nvmem
+
+  reg:
+    maxItems: 1
+
+  reg-io-width:
+    description: |
+      The size (in bytes) of the IO accesses that should be performed
+      on the device.
+    enum: [1, 2, 4, 8]
+
+required:
+  - reg
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    nvmem@...00 {
+        compatible = "mmio-nvmem";
+        reg = <0x10000000 0x10000>;
+    };
-- 
2.34.1