[PATCH v2 2/4] dt-bindings: nvmem: layouts: Add Rockchip OTP CPUID layout

[Alexey Charkov <alchark@flipper.net>]

Rockchip SoCs ship with a unique CPU ID programmed into their internal OTP
memory, and Rockchip bootloaders derive Ethernet MAC addresses from it so
that boards with no dedicated storage for one still get a stable address.

Describe that derivation as an NVMEM layout, so that the resulting
addresses become available through the standard nvmem "mac-address" cell
whether or not the firmware got a chance to patch them into the device
tree. Keep the compatible SoC specific, as the location of the CPU ID
within the OTP memory differs between SoCs.

Signed-off-by: Alexey Charkov <alchark@flipper.net>
---
 .../bindings/nvmem/layouts/nvmem-layout.yaml       |  1 +
 .../nvmem/layouts/rockchip,rk3576-otp-cpuid.yaml   | 73 ++++++++++++++++++++++
 MAINTAINERS                                        |  6 ++
 3 files changed, 80 insertions(+)

diff --git a/Documentation/devicetree/bindings/nvmem/layouts/nvmem-layout.yaml b/Documentation/devicetree/bindings/nvmem/layouts/nvmem-layout.yaml
index 382507060651..ab94dbb41aac 100644
--- a/Documentation/devicetree/bindings/nvmem/layouts/nvmem-layout.yaml
+++ b/Documentation/devicetree/bindings/nvmem/layouts/nvmem-layout.yaml
@@ -21,6 +21,7 @@ oneOf:
   - $ref: fixed-layout.yaml
   - $ref: kontron,sl28-vpd.yaml
   - $ref: onie,tlv-layout.yaml
+  - $ref: rockchip,rk3576-otp-cpuid.yaml
   - $ref: u-boot,env.yaml
 
 properties:
diff --git a/Documentation/devicetree/bindings/nvmem/layouts/rockchip,rk3576-otp-cpuid.yaml b/Documentation/devicetree/bindings/nvmem/layouts/rockchip,rk3576-otp-cpuid.yaml
new file mode 100644
index 000000000000..85153d480950
--- /dev/null
+++ b/Documentation/devicetree/bindings/nvmem/layouts/rockchip,rk3576-otp-cpuid.yaml
@@ -0,0 +1,73 @@
+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/nvmem/layouts/rockchip,rk3576-otp-cpuid.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: NVMEM layout of the CPU ID in Rockchip OTP memory
+
+maintainers:
+  - Alexey Charkov <alchark@flipper.net>
+
+description: |
+  Rockchip SoCs are shipped with a unique CPU ID programmed into their
+  internal OTP memory. Rockchip bootloaders derive Ethernet MAC addresses
+  from it, so that boards which have no dedicated storage for a MAC address
+  still get a stable one. The addresses are computed by hashing the lowercase
+  hexadecimal representation of the CPU ID with SHA-256 and taking the first
+  six octets of the digest, with the multicast bit cleared and the locally
+  administered bit set.
+
+  The location of the CPU ID within the OTP memory differs between SoCs,
+  hence the SoC specific compatible.
+
+select: false
+
+properties:
+  compatible:
+    const: rockchip,rk3576-otp-cpuid
+
+  mac-address:
+    type: object
+    description:
+      MAC address derived from the CPU ID. The first argument of the phandle
+      selects one of the two addresses that can be derived (can be 0 or 1).
+
+    properties:
+      "#nvmem-cell-cells":
+        const: 1
+
+    additionalProperties: false
+
+required:
+  - compatible
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/clock/rockchip,rk3576-cru.h>
+    #include <dt-bindings/reset/rockchip,rk3576-cru.h>
+
+    soc {
+        #address-cells = <2>;
+        #size-cells = <2>;
+
+        otp@2a580000 {
+            compatible = "rockchip,rk3576-otp";
+            reg = <0x0 0x2a580000 0x0 0x400>;
+            clocks = <&cru CLK_OTPC_NS>, <&cru PCLK_OTPC_NS>,
+                     <&cru CLK_OTP_PHY_G>;
+            clock-names = "otp", "apb_pclk", "phy";
+            resets = <&cru SRST_OTPC_NS>, <&cru SRST_P_OTPC_NS>;
+            reset-names = "otp", "apb";
+
+            nvmem-layout {
+                compatible = "rockchip,rk3576-otp-cpuid";
+
+                otp_mac_address: mac-address {
+                    #nvmem-cell-cells = <1>;
+                };
+            };
+        };
+    };
diff --git a/MAINTAINERS b/MAINTAINERS
index eb4e5a61056e..f3d07ce7b3c8 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -23722,6 +23722,12 @@ F:	Documentation/userspace-api/media/v4l/metafmt-rkisp1.rst
 F:	drivers/media/platform/rockchip/rkisp1
 F:	include/uapi/linux/rkisp1-config.h
 
+ROCKCHIP OTP CPUID NVMEM LAYOUT DRIVER
+M:	Alexey Charkov <alchark@flipper.net>
+L:	linux-rockchip@lists.infradead.org
+S:	Maintained
+F:	Documentation/devicetree/bindings/nvmem/layouts/rockchip,rk3576-otp-cpuid.yaml
+
 ROCKCHIP RK3568 RANDOM NUMBER GENERATOR SUPPORT
 M:	Daniel Golle <daniel@makrotopia.org>
 M:	Aurelien Jarno <aurelien@aurel32.net>

-- 
2.54.0