drivers: entropy: add puf-trng entropy driver

add puf-trng entropy driver to apollo510

Signed-off-by: Richard Wheatley <richard.wheatley@ambiq.com>

boards/ambiq/apollo510_evb/apollo510_evb.dts

@@ -15,6 +15,7 @@
 		zephyr,console = &uart0;
 		zephyr,shell-uart = &uart0;
 		zephyr,uart-pipe = &uart0;
+		zephyr,entropy = &trng;
 		ambiq,xo32m = &xo32m_xtal;
 		ambiq,xo32k = &xo32k_xtal;
 		ambiq,extrefclk = &extrefclk;
@@ -90,6 +91,10 @@
 	};
 };
 
+&trng {
+	status = "okay";
+};
+
 &xo32m_xtal {
 	clock-frequency = <DT_FREQ_M(48)>;
 };

drivers/entropy/CMakeLists.txt

@@ -12,6 +12,7 @@ endif()
 zephyr_library_sources_ifdef(CONFIG_USERSPACE entropy_handlers.c)
 
 # zephyr-keep-sorted-start
+zephyr_library_sources_ifdef(CONFIG_ENTROPY_AMBIQ_PUF_TRNG      entropy_ambiq_puf_trng.c)
 zephyr_library_sources_ifdef(CONFIG_ENTROPY_BRCM_IPROC_RNG200   entropy_iproc_rng200.c)
 zephyr_library_sources_ifdef(CONFIG_ENTROPY_BT_HCI              entropy_bt_hci.c)
 zephyr_library_sources_ifdef(CONFIG_ENTROPY_CC13XX_CC26XX_RNG   entropy_cc13xx_cc26xx.c)

drivers/entropy/Kconfig

@@ -21,6 +21,7 @@ config ENTROPY_INIT_PRIORITY
 	  Entropy driver device initialization priority.
 
 # zephyr-keep-sorted-start
+source "drivers/entropy/Kconfig.ambiq"
 source "drivers/entropy/Kconfig.b91"
 source "drivers/entropy/Kconfig.bt_hci"
 source "drivers/entropy/Kconfig.cc13xx_cc26xx"

drivers/entropy/Kconfig.ambiq

@@ -0,0 +1,14 @@
+# PUF entropy generator driver configuration
+
+# Copyright (c) 2025, Ambiq Micro, Inc.
+# SPDX-License-Identifier: Apache-2.0
+
+config ENTROPY_AMBIQ_PUF_TRNG
+	bool "Ambiq TRNG driver"
+	default y
+	depends on SOC_AMBIQ_HAS_PUF
+	depends on DT_HAS_AMBIQ_PUF_TRNG_ENABLED
+	select ENTROPY_HAS_DRIVER
+	help
+	  This option enables the true random number generator
+	  driver based on the OTP/PUF TRNG.

drivers/entropy/entropy_ambiq_puf_trng.c

@@ -0,0 +1,103 @@
+/*
+ * Copyright (c) 2025 Ambiq Micro, Inc.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#define DT_DRV_COMPAT ambiq_puf_trng
+
+#include <string.h>
+#include "soc.h"
+#include <zephyr/logging/log.h>
+#include <zephyr/drivers/entropy.h>
+
+LOG_MODULE_REGISTER(ambiq_puf_trng_entropy, CONFIG_ENTROPY_LOG_LEVEL);
+
+/*
+ * Select the correct TRNG memory base address.
+ *
+ * The TRNG is implemented in the OTP memory
+ * and the TRNG address is memory mapped to the OTP.
+ *
+ */
+#define TRNG_BASE DT_INST_REG_ADDR(0)
+
+/* Max Fail Count  for errors */
+#define MAX_FAIL_COUNT 5
+
+static inline uint32_t get_trng_u32(void)
+{
+	return AM_REGVAL(TRNG_BASE);
+}
+
+static int entropy_ambiq_get_trng(const struct device *dev, uint8_t *buffer, uint16_t length)
+{
+	ARG_UNUSED(dev);
+
+	/* Validate input parameters */
+	if (length == 0 || buffer == NULL) {
+		return -EINVAL;
+	}
+
+	uint8_t *byte_buffer = buffer;
+	uint8_t fail_cnt = 0;
+
+	/*
+	 * While the passed in length is greater than zero
+	 * grab data from RNG and save to output.
+	 */
+	while ((length > 0) && (fail_cnt < MAX_FAIL_COUNT)) {
+		uint32_t word = get_trng_u32();
+
+		/* This is a failure mode where the RNG doesn't have enough randomness */
+		if (word == 0xdeaddead) {
+			fail_cnt++;
+			continue;
+		}
+
+		size_t copy_length = MIN(sizeof(uint32_t), length);
+		/*
+		 * If the length is less than 4 bytes, we only copy the
+		 * requested number of bytes.
+		 */
+		memcpy(byte_buffer, &word, copy_length);
+		byte_buffer += copy_length;
+		length -= copy_length;
+	}
+
+	if (fail_cnt >= MAX_FAIL_COUNT) {
+		return -EIO;
+	}
+
+	return 0;
+}
+
+static int entropy_ambiq_trng_init(const struct device *dev)
+{
+	uint32_t status;
+	bool peripheral_enabled = false;
+
+	/* Check and Power on OTP if it is not already on. */
+	status = am_hal_pwrctrl_periph_enabled(AM_HAL_PWRCTRL_PERIPH_OTP, &peripheral_enabled);
+	if (status != AM_HAL_STATUS_SUCCESS) {
+		LOG_ERR("Failed to check OTP peripheral status, error: 0x%x", status);
+		return -EBUSY;
+	}
+
+	if (!peripheral_enabled) {
+		status = am_hal_pwrctrl_periph_enable(AM_HAL_PWRCTRL_PERIPH_OTP);
+		if (status != AM_HAL_STATUS_SUCCESS) {
+			LOG_ERR("Failed to enable OTP peripheral, error: 0x%x", status);
+			return -EBUSY;
+		}
+	}
+
+	return 0;
+}
+
+static DEVICE_API(entropy, entropy_ambiq_api_funcs) = {
+	.get_entropy = entropy_ambiq_get_trng,
+};
+
+DEVICE_DT_INST_DEFINE(0, entropy_ambiq_trng_init, NULL, NULL, NULL, PRE_KERNEL_1,
+			  CONFIG_ENTROPY_INIT_PRIORITY, &entropy_ambiq_api_funcs);

dts/arm/ambiq/ambiq_apollo510.dtsi

@@ -137,6 +137,12 @@
 	soc {
 		compatible = "ambiq,apollo510", "ambiq,apollo5x", "simple-bus";
 
+		trng: trng@40014aa0 {
+			compatible = "ambiq,puf-trng";
+			reg = <0x40014aa0 0x4>;
+			status = "disabled";
+		};
+
 		stimer0: stimer@STIMER_BASE_NAME {
 			compatible = "ambiq,stimer";
 			reg = <STIMER_REG_BASE STIMER_REG_SIZE>;

dts/bindings/rng/ambiq,puf-trng.yaml

@@ -0,0 +1,16 @@
+# Copyright (c) 2025, Ambiq
+# Author: Richard S Wheatley
+# SPDX-License-Identifier: Apache-2.0
+
+description: |
+    PUF TRNG (True Random Number Generator).
+
+    This module is a non-deterministic random number generator based on a full hardware solution.
+
+compatible: "ambiq,puf-trng"
+
+include: base.yaml
+
+properties:
+  reg:
+    required: true

soc/ambiq/apollo5x/Kconfig

@@ -20,6 +20,13 @@ config SOC_SERIES_APOLLO5X
 	select SOC_EARLY_INIT_HOOK
 	select REQUIRES_FULL_LIBC
 
+config SOC_AMBIQ_HAS_PUF
+	bool "Ambiq PUF support"
+	default y
+	help
+	  This option enables the Ambiq PUF support.
+	  It is required for the true random number generator.
+
 config SOC_AMBIQ_DCACHE_SIZE
 	int
 	default 65536 if SOC_APOLLO510