subsys/random: sys_rand32_get() implementation that uses entropy API

Instead of every hardware number generator driver providing an
implementation of this function, use the random device API to
centralize the implementation of this function.

This is a very simplistic function that can be seen as a stepping stone
to refactor the random number generation in Zephyr.

Signed-off-by: Leandro Pereira <leandro.pereira@intel.com>

drivers/entropy/Kconfig.esp32

@@ -9,7 +9,6 @@ config ENTROPY_ESP32_RNG
 	depends on ENTROPY_GENERATOR && SOC_ESP32
 	default n
 	select ENTROPY_HAS_DRIVER
-	select ENTROPY_DEVICE_ENTROPY_GENERATOR
 	help
 	  This option enables the entropy number generator for ESP32 SoCs.
 

drivers/entropy/Kconfig.mcux

@@ -9,6 +9,7 @@ menuconfig ENTROPY_MCUX_RNGA
 	depends on ENTROPY_GENERATOR && HAS_MCUX_RNGA
 	default n
 	select ENTROPY_HAS_DRIVER
+	select ENTROPY_DEVICE_RANDOM_GENERATOR
 	help
 	  This option enables the random number generator accelerator (RNGA)
 	  driver based on the MCUX RNGA driver.
@@ -18,6 +19,7 @@ menuconfig ENTROPY_MCUX_TRNG
 	depends on ENTROPY_GENERATOR && HAS_MCUX_TRNG
 	default n
 	select ENTROPY_HAS_DRIVER
+	select ENTROPY_DEVICE_RANDOM_GENERATOR
 	help
 	  This option enables the true random number generator (TRNG)
 	  driver based on the MCUX TRNG driver.

drivers/entropy/Kconfig.stm32

@@ -9,7 +9,6 @@ menuconfig ENTROPY_STM32_RNG
 	depends on ENTROPY_GENERATOR
 	default n
 	select ENTROPY_HAS_DRIVER
-	select ENTROPY_DEVICE_ENTROPY_GENERATOR
 	help
 	  This option enables the RNG processor, which is a entropy number
 	  generator, based on a continuous analog noise, that provides

drivers/entropy/entropy_esp32.c

@@ -57,8 +57,3 @@ DEVICE_AND_API_INIT(entropy_esp32, CONFIG_ENTROPY_NAME,
 		    entropy_esp32_init, NULL, NULL,
 		    PRE_KERNEL_1, CONFIG_KERNEL_INIT_PRIORITY_DEVICE,
 		    &entropy_esp32_api_funcs);
-
-u32_t sys_rand32_get(void)
-{
-	return random_esp32_get_u32();
-}

drivers/entropy/entropy_mcux_rnga.c

@@ -79,15 +79,3 @@ static int entropy_mcux_rnga_init(struct device *dev)
 	RNGA_SetMode(RNG, kRNGA_ModeSleep);
 	return 0;
 }
-
-u32_t sys_rand32_get(void)
-{
-	u32_t output;
-	int r;
-
-	r = random_mcux_rnga_get_entropy(DEVICE_GET(random_mcux_rnga),
-					 (u8_t *) &output, sizeof(output));
-	__ASSERT_NO_MSG(!r);
-
-	return output;
-}

drivers/entropy/entropy_mcux_trng.c

@@ -50,15 +50,3 @@ static int entropy_mcux_trng_init(struct device *dev)
 
 	return 0;
 }
-
-u32_t sys_rand32_get(void)
-{
-	u32_t output;
-	int rc;
-
-	rc = random_mcux_trng_get_entropy(DEVICE_GET(random_mcux_trng),
-					  (u8_t *) &output, sizeof(output));
-	__ASSERT_NO_MSG(!rc);
-
-	return output;
-}

drivers/entropy/entropy_stm32.c

@@ -181,15 +181,3 @@ DEVICE_AND_API_INIT(entropy_stm32_rng, CONFIG_ENTROPY_NAME,
 		    &entropy_stm32_rng_data, &entropy_stm32_rng_config,
 		    PRE_KERNEL_2, CONFIG_KERNEL_INIT_PRIORITY_DEVICE,
 		    &entropy_stm32_rng_api);
-
-u32_t sys_rand32_get(void)
-{
-	u32_t output;
-	int rc;
-
-	rc = random_stm32_rng_get_entropy(DEVICE_GET(random_stm32_rng),
-					  (u8_t *) &output, sizeof(output));
-	__ASSERT_NO_MSG(!rc);
-
-	return output;
-}

subsys/random/Kconfig

@@ -33,3 +33,12 @@ config TIMER_RANDOM_GENERATOR
 	  This options enables number generator based on system timer
 	  clock. This number generator is not random and used for
 	  testing only.
+
+config ENTROPY_DEVICE_RANDOM_GENERATOR
+	bool
+	prompt "Use entropy driver to generate random numbers"
+	depends on ENTROPY_HAS_DRIVER
+	help
+	  Enables a random number generator that uses the enabled
+	  hardware entropy gathering driver to generate random
+	  numbers.

subsys/random/Makefile

@@ -1,2 +1,3 @@
 obj-$(CONFIG_TIMER_RANDOM_GENERATOR) = rand32_timer.o
 obj-$(CONFIG_X86_TSC_RANDOM_GENERATOR) += rand32_timestamp.o
+obj-$(CONFIG_ENTROPY_DEVICE_RANDOM_GENERATOR) += rand32_entropy_device.o

subsys/random/rand32_entropy_device.c

@@ -0,0 +1,40 @@
+/*
+ * Copyright (c) 2017 Intel Corporation
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <atomic.h>
+#include <kernel.h>
+#include <entropy.h>
+
+static atomic_t entropy_driver;
+
+u32_t sys_rand32_get(void)
+{
+	struct device *dev = (struct device *)atomic_get(&entropy_driver);
+	u32_t random_num;
+	int ret;
+
+	if (unlikely(!dev)) {
+		/* Only one entropy device exists, so this is safe even
+		 * if the whole operation isn't atomic.
+		 */
+		dev = device_get_binding(CONFIG_ENTROPY_NAME);
+		atomic_set(&entropy_driver, (atomic_t)(uintptr_t)dev);
+	}
+
+	ret = entropy_get_entropy(dev, (u8_t *)&random_num,
+				  sizeof(random_num));
+	if (unlikely(ret < 0)) {
+		/* Use system timer in case the entropy device couldn't deliver
+		 * 32-bit of data.  There's not much that can be done in this
+		 * situation.  An __ASSERT() isn't used here as the HWRNG might
+		 * still be gathering entropy during early boot situations.
+		 */
+
+		random_num = k_cycle_get_32();
+	}
+
+	return random_num;
+}