[PATCH 1/2] hwrng: Add support for ASPEED RNG

[Oscar A Perez]

This minimal driver adds support for the Hardware Random Number Generator
that comes with the AST2400/AST2500/AST2600 SOCs from AspeedTech.

The HRNG on these SOCs uses Ring Oscillators working together to generate
a stream of random bits that can be read by the platform via a 32bit data
register.

Signed-off-by: Oscar A Perez <linux at neuralgames.com>
---
 .../devicetree/bindings/rng/aspeed-rng.yaml   | 90 +++++++++++++++++++
 1 file changed, 90 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/rng/aspeed-rng.yaml

diff --git a/Documentation/devicetree/bindings/rng/aspeed-rng.yaml b/Documentation/devicetree/bindings/rng/aspeed-rng.yaml
new file mode 100644
index 000000000000..06070ebe1c33
--- /dev/null
+++ b/Documentation/devicetree/bindings/rng/aspeed-rng.yaml
@@ -0,0 +1,90 @@
+# SPDX-License-Identifier: GPL-2.0
+%YAML 1.2
+---
+$id: "http://devicetree.org/schemas/rng/aspeed-rng.yaml#"
+$schema: "http://devicetree.org/meta-schemas/core.yaml#"
+
+
+title: Bindings for Aspeed Hardware Random Number Generator
+
+
+maintainers:
+  - Oscar A Perez <linux at neuralgames.com>
+
+
+description: |
+  The HRNG on the AST2400/AST2500/AST2600 SOCs from AspeedTech  uses four Ring
+  Oscillators working together to generate a stream of random bits that can be
+  read by the platform via a 32bit data register every one microsecond.
+  All the platform has to do is to provide to the driver the 'quality' entropy
+  value, the  'mode' in which the combining  ROs will generate the  stream  of
+  random bits and, the 'period' value that is used as a wait-time between reads
+  from the 32bit data register.
+
+
+properties:
+  compatible:
+    oneOf:
+      - items:
+          - enum:
+              - aspeed,ast2400-rng
+              - aspeed,ast2500-rng
+              - aspeed,ast2600-rng
+
+
+  reg:
+    description:
+      Base address and length of the register set of this block.
+      Currently 'reg' must be eight bytes wide and 32-bit aligned.
+
+    maxItems: 1
+
+
+  period:
+    description:
+      Wait time in microseconds to be used between reads.
+      The RNG on these Aspeed SOCs generates 32bit of random data
+      every one microsecond. Choose between 1 and n microseconds.
+
+    maxItems: 1
+
+
+  mode:
+    description:
+      One of the eight modes in which the four internal ROs (Ring
+      Oscillators)  are combined to generate a stream  of random
+      bits. The default mode is seven which is the default method
+      of combining RO random bits on these Aspeed SOCs.
+
+    maxItems: 1
+
+
+  quality:
+    description:
+      Estimated number of bits of entropy per 1024 bits read from
+      the RNG.  Note that the default quality is zero which stops
+      this HRNG from automatically filling the kernel's entropy
+      pool with data.
+
+    maxItems: 1
+
+
+required:
+  - compatible
+  - reg
+  - period
+  - quality
+
+
+examples:
+  - |
+    rng: hwrng at 1e6e2074 {
+         compatible = "aspeed,ast2500-rng";
+         reg = <0x1e6e2074 0x8>;
+         period = <4>;
+         quality = <128>;
+         mode = <0x7>;
+    };
+
+
+...
-- 
2.17.1