drivers: entropy: Add nRF5 entropy generator driver

Origin: Original

Signed-off-by: Thiago Silveira <thiago@exati.com.br>
Signed-off-by: Andrzej Głąbek <andrzej.glabek@nordicsemi.no>

drivers/entropy/CMakeLists.txt

@@ -1,5 +1,6 @@
 zephyr_sources_ifdef(CONFIG_ENTROPY_ESP32_RNG          entropy_esp32.c)
 zephyr_sources_ifdef(CONFIG_ENTROPY_MCUX_RNGA          entropy_mcux_rnga.c)
 zephyr_sources_ifdef(CONFIG_ENTROPY_MCUX_TRNG          entropy_mcux_trng.c)
+zephyr_sources_ifdef(CONFIG_ENTROPY_NRF5_RNG           entropy_nrf5.c)
 zephyr_sources_ifdef(CONFIG_ENTROPY_STM32_RNG          entropy_stm32_rng.c)
 zephyr_sources_ifdef(CONFIG_USERSPACE                  entropy_handlers.c)

drivers/entropy/Kconfig

@@ -18,6 +18,7 @@ if ENTROPY_GENERATOR
 source "drivers/entropy/Kconfig.mcux"
 source "drivers/entropy/Kconfig.stm32"
 source "drivers/entropy/Kconfig.esp32"
+source "drivers/entropy/Kconfig.nrf5"
 
 config ENTROPY_HAS_DRIVER
 	bool

drivers/entropy/Kconfig.nrf5

@@ -0,0 +1,25 @@
+# Kconfig.nrf5 - nRF5 entropy generator driver configuration
+#
+# Copyright (c) 2017 Nordic Semiconductor ASA
+# Copyright (c) 2017 Exati Tecnologia Ltda.
+#
+# SPDX-License-Identifier: Apache-2.0
+
+menuconfig ENTROPY_NRF5_RNG
+	bool "nRF5 RNG driver"
+	# FIXME: nRF5 RNG driver can't co-exist with Bluetooth's HAL
+	# implementation yet
+	depends on ENTROPY_GENERATOR && !BT
+	select ENTROPY_HAS_DRIVER
+	help
+	  This option enables the RNG peripheral, which is a random number
+	  generator, based on internal thermal noise, that provides a
+	  random 8-bit value to the host when read.
+
+config ENTROPY_NRF5_BIAS_CORRECTION
+	bool "Enable bias correction (uniform distribution)"
+	depends on ENTROPY_NRF5_RNG
+	help
+	  This option enables the RNG bias correction, which guarantees a
+	  uniform distribution of 0 and 1. When this option is enabled, the time
+	  to generate a byte cannot be guaranteed.

drivers/entropy/entropy_nrf5.c

@@ -0,0 +1,102 @@
+/*
+ * Copyright (c) 2017 Nordic Semiconductor ASA
+ * Copyright (c) 2017 Exati Tecnologia Ltda.
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <entropy.h>
+#include <atomic.h>
+#include <nrf_rng.h>
+
+struct entropy_nrf5_dev_data {
+	atomic_t user_count;
+};
+
+#define DEV_DATA(dev) \
+	((struct entropy_nrf5_dev_data *)(dev)->driver_data)
+
+static inline u8_t entropy_nrf5_get_u8(void)
+{
+	while (!nrf_rng_event_get(NRF_RNG_EVENT_VALRDY)) {
+		__WFE();
+		__SEV();
+		__WFE();
+	}
+	nrf_rng_event_clear(NRF_RNG_EVENT_VALRDY);
+
+	/* Clear the Pending status of the RNG interrupt so that it could
+	 * wake up the core when the VALRDY event occurs again. */
+	NVIC_ClearPendingIRQ(RNG_IRQn);
+
+	return nrf_rng_random_value_get();
+}
+
+static int entropy_nrf5_get_entropy(struct device *device, u8_t *buf, u16_t len)
+{
+	/* Mark the peripheral as being used */
+	atomic_inc(&DEV_DATA(device)->user_count);
+
+	/* Disable the shortcut that stops the task after a byte is generated */
+	nrf_rng_shorts_disable(NRF_RNG_SHORT_VALRDY_STOP_MASK);
+
+	/* Start the RNG generator peripheral */
+	nrf_rng_task_trigger(NRF_RNG_TASK_START);
+
+	while (len) {
+		*buf = entropy_nrf5_get_u8();
+		buf++;
+		len--;
+	}
+
+	/* Only stop the RNG generator peripheral if we're the last user */
+	if (atomic_dec(&DEV_DATA(device)->user_count) == 1) {
+		/* Disable the peripheral on the next VALRDY event */
+		nrf_rng_shorts_enable(NRF_RNG_SHORT_VALRDY_STOP_MASK);
+
+		if (atomic_get(&DEV_DATA(device)->user_count) != 0) {
+			/* Race condition: another thread started to use
+			 * the peripheral while we were disabling it.
+			 * Enable the peripheral again
+			 */
+			nrf_rng_shorts_disable(NRF_RNG_SHORT_VALRDY_STOP_MASK);
+			nrf_rng_task_trigger(NRF_RNG_TASK_START);
+		}
+	}
+
+	return 0;
+}
+
+static int entropy_nrf5_init(struct device *device)
+{
+	/* Enable the RNG interrupt to be generated on the VALRDY event,
+	 * but do not enable this interrupt in NVIC to be serviced.
+	 * When the interrupt enters the Pending state it will set internal
+	 * event (SEVONPEND is activated by kernel) and wake up the core
+	 * if it was suspended by WFE. And that's enough. */
+	nrf_rng_int_enable(NRF_RNG_INT_VALRDY_MASK);
+	NVIC_ClearPendingIRQ(RNG_IRQn);
+
+	/* Enable or disable bias correction */
+	if (IS_ENABLED(CONFIG_ENTROPY_NRF5_BIAS_CORRECTION)) {
+		nrf_rng_error_correction_enable();
+	} else {
+		nrf_rng_error_correction_disable();
+	}
+
+	/* Initialize the user count with zero */
+	atomic_clear(&DEV_DATA(device)->user_count);
+
+	return 0;
+}
+
+static struct entropy_nrf5_dev_data entropy_nrf5_data;
+
+static const struct entropy_driver_api entropy_nrf5_api_funcs = {
+	.get_entropy = entropy_nrf5_get_entropy
+};
+
+DEVICE_AND_API_INIT(entropy_nrf5, CONFIG_ENTROPY_NAME,
+		    entropy_nrf5_init, &entropy_nrf5_data, NULL,
+		    PRE_KERNEL_1, CONFIG_KERNEL_INIT_PRIORITY_DEVICE,
+		    &entropy_nrf5_api_funcs);