drivers: entropy: add driver for the neorv32 trng

Add entropy driver for the NEORV32 True Random Number Generator (TRNG).

Signed-off-by: Henrik Brix Andersen <henrik@brixandersen.dk>

drivers/entropy/CMakeLists.txt

@@ -16,3 +16,4 @@ zephyr_library_sources_ifdef(CONFIG_FAKE_ENTROPY_NATIVE_POSIX  fake_entropy_nati
 zephyr_library_sources_ifdef(CONFIG_USERSPACE                  entropy_handlers.c)
 zephyr_library_sources_ifdef(CONFIG_ENTROPY_RV32M1_TRNG        entropy_rv32m1_trng.c)
 zephyr_library_sources_ifdef(CONFIG_ENTROPY_GECKO_TRNG         entropy_gecko_trng.c)
+zephyr_library_sources_ifdef(CONFIG_ENTROPY_NEORV32_TRNG       entropy_neorv32_trng.c)

drivers/entropy/Kconfig

@@ -31,6 +31,7 @@ source "drivers/entropy/Kconfig.native_posix"
 source "drivers/entropy/Kconfig.rv32m1"
 source "drivers/entropy/Kconfig.litex"
 source "drivers/entropy/Kconfig.gecko"
+source "drivers/entropy/Kconfig.neorv32"
 
 config ENTROPY_HAS_DRIVER
 	bool

drivers/entropy/Kconfig.neorv32

@@ -0,0 +1,13 @@
+# NEORV32 TRNG configuration
+
+# Copyright (c) 2021 Henrik Brix Andersen <henrik@brixandersen.dk>
+# SPDX-License-Identifier: Apache-2.0
+
+config ENTROPY_NEORV32_TRNG
+	bool "NEORV32 TRNG"
+	default $(dt_compat_enabled,neorv32-trng)
+	depends on SOC_SERIES_NEORV32 && SYSCON
+	select ENTROPY_HAS_DRIVER
+	help
+	  This option enables the True Random Number Generator (TRNG) driver for
+	  the NEORV32.

drivers/entropy/entropy_neorv32_trng.c

@@ -0,0 +1,152 @@
+/*
+ * Copyright (c) 2021 Henrik Brix Andersen <henrik@brixandersen.dk>
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#define DT_DRV_COMPAT neorv32_trng
+
+#include <device.h>
+#include <drivers/syscon.h>
+#include <drivers/entropy.h>
+#include <sys/sys_io.h>
+
+#include <logging/log.h>
+LOG_MODULE_REGISTER(neorv32_trng, CONFIG_ENTROPY_LOG_LEVEL);
+
+/* TRNG CTRL register bits */
+#define NEORV32_TRNG_CTRL_DATA_MASK BIT_MASK(8)
+#define NEORV32_TRNG_CTRL_EN        BIT(30)
+#define NEORV32_TRNG_CTRL_VALID     BIT(31)
+
+struct neorv32_trng_config {
+	const struct device *syscon;
+	mm_reg_t base;
+};
+
+static inline uint32_t neorv32_trng_read_ctrl(const struct device *dev)
+{
+	const struct neorv32_trng_config *config = dev->config;
+
+	return sys_read32(config->base);
+}
+
+static inline void neorv32_trng_write_ctrl(const struct device *dev, uint32_t ctrl)
+{
+	const struct neorv32_trng_config *config = dev->config;
+
+	sys_write32(ctrl, config->base);
+}
+
+static int neorv32_trng_get_entropy(const struct device *dev, uint8_t *buffer, uint16_t len)
+{
+	uint32_t ctrl;
+
+	while (len > 0) {
+		ctrl = neorv32_trng_read_ctrl(dev);
+
+		if ((ctrl & NEORV32_TRNG_CTRL_VALID) != 0) {
+			*buffer++ = ctrl & NEORV32_TRNG_CTRL_DATA_MASK;
+			len--;
+		}
+	}
+
+	return 0;
+}
+
+static int neorv32_trng_get_entropy_isr(const struct device *dev, uint8_t *buffer,
+					uint16_t len, uint32_t flags)
+{
+	uint32_t ctrl;
+	int err;
+
+	if ((flags & ENTROPY_BUSYWAIT) == 0) {
+		ctrl = neorv32_trng_read_ctrl(dev);
+		if ((ctrl & NEORV32_TRNG_CTRL_VALID) != 0) {
+			*buffer = ctrl & NEORV32_TRNG_CTRL_DATA_MASK;
+			return 1;
+		}
+
+		/* No entropy available */
+		return 0;
+	}
+
+	err = neorv32_trng_get_entropy(dev, buffer, len);
+	if (err < 0) {
+		return err;
+	}
+
+	return len;
+}
+
+static int neorv32_trng_init(const struct device *dev)
+{
+	const struct neorv32_trng_config *config = dev->config;
+	uint32_t features;
+	int err;
+
+	if (!device_is_ready(config->syscon)) {
+		LOG_ERR("syscon device not ready");
+		return -EINVAL;
+	}
+
+	err = syscon_read_reg(config->syscon, NEORV32_SYSINFO_FEATURES, &features);
+	if (err < 0) {
+		LOG_ERR("failed to determine implemented features (err %d)", err);
+		return err;
+	}
+
+	if ((features & NEORV32_SYSINFO_FEATURES_IO_TRNG) == 0) {
+		LOG_ERR("neorv32 trng not supported");
+		return -ENODEV;
+	}
+
+	neorv32_trng_write_ctrl(dev, NEORV32_TRNG_CTRL_EN);
+
+	return 0;
+}
+
+#ifdef CONFIG_PM_DEVICE
+static int neorv32_trng_pm_action(const struct device *dev, enum pm_device_action action)
+{
+	switch (action) {
+	case PM_DEVICE_ACTION_SUSPEND:
+		neorv32_trng_write_ctrl(dev, 0);
+		break;
+	case PM_DEVICE_ACTION_RESUME:
+		neorv32_trng_write_ctrl(dev, NEORV32_TRNG_CTRL_EN);
+		break;
+	default:
+		return -ENOTSUP;
+	}
+
+	return 0;
+}
+#endif /* CONFIG_PM_DEVICE */
+
+static const struct entropy_driver_api neorv32_trng_driver_api = {
+	.get_entropy = neorv32_trng_get_entropy,
+	.get_entropy_isr = neorv32_trng_get_entropy_isr,
+};
+
+#ifdef CONFIG_PM_DEVICE
+#define NEORV32_TRNG_PM_ACTION_CB neorv32_trng_pm_action
+#else /* CONFIG_PM_DEVICE */
+#define NEORV32_TRNG_PM_ACTION_CB NULL
+#endif /* ! CONFIG_PM_DEVICE */
+
+#define NEORV32_TRNG_INIT(n)						\
+	static const struct neorv32_trng_config neorv32_trng_##n##_config = { \
+		.syscon = DEVICE_DT_GET(DT_INST_PHANDLE(n, syscon)),	\
+		.base = DT_INST_REG_ADDR(n),				\
+	};								\
+									\
+	DEVICE_DT_INST_DEFINE(n, &neorv32_trng_init,			\
+			 NEORV32_TRNG_PM_ACTION_CB,			\
+			 NULL,						\
+			 &neorv32_trng_##n##_config,			\
+			 PRE_KERNEL_1,					\
+			 CONFIG_ENTROPY_INIT_PRIORITY,			\
+			 &neorv32_trng_driver_api);
+
+DT_INST_FOREACH_STATUS_OKAY(NEORV32_TRNG_INIT)

soc/riscv/riscv-privilege/neorv32/Kconfig.defconfig.series

@@ -25,4 +25,8 @@ config SERIAL_INIT_PRIORITY
 	default 55
 	depends on SERIAL
 
+config ENTROPY_INIT_PRIORITY
+	default 55
+	depends on ENTROPY_GENERATOR
+
 endif # SOC_SERIES_NEORV32