sandbox: rng: Add a random number generator(rng) driver

Add a sandbox driver for random number generation. Mostly aimed at
providing a unit test for rng uclass.

Signed-off-by: Sughosh Ganu <sughosh.ganu@linaro.org>
Reviewed-by: Patrice Chotard <patrice.chotard@st.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

arch/sandbox/dts/test.dts

@@ -630,6 +630,10 @@
 		reset-names = "other", "test";
 	};
 
+	rng {
+		compatible = "sandbox,sandbox-rng";
+	};
+
 	rproc_1: rproc@1 {
 		compatible = "sandbox,test-processor";
 		remoteproc-name = "remoteproc-test-dev1";

drivers/rng/Kconfig

@@ -6,6 +6,14 @@ config DM_RNG
 	  This interface is used to initialise the rng device and to
 	  read the random seed from the device.
 
+config RNG_SANDBOX
+	bool "Sandbox random number generator"
+	depends on SANDBOX && DM_RNG
+	select CONFIG_LIB_RAND
+	help
+	  Enable random number generator for sandbox. This is an
+	  emulation of a rng device.
+
 config RNG_STM32MP1
 	bool "Enable random number generator for STM32MP1"
 	depends on ARCH_STM32MP && DM_RNG

drivers/rng/Makefile

@@ -4,4 +4,5 @@
 #
 
 obj-$(CONFIG_DM_RNG) += rng-uclass.o
+obj-$(CONFIG_RNG_SANDBOX) += sandbox_rng.o
 obj-$(CONFIG_RNG_STM32MP1) += stm32mp1_rng.o

drivers/rng/sandbox_rng.c

@@ -0,0 +1,56 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2019, Linaro Limited
+ */
+
+#include <common.h>
+#include <dm.h>
+#include <rng.h>
+
+#include <linux/string.h>
+
+static int sandbox_rng_read(struct udevice *dev, void *data, size_t len)
+{
+	unsigned int i, seed, random;
+	unsigned char *buf = data;
+	size_t nrem, nloops;
+
+	if (!len)
+		return 0;
+
+	nloops = len / sizeof(random);
+	seed = get_timer(0) ^ rand();
+	srand(seed);
+
+	for (i = 0, nrem = len; i < nloops; i++) {
+		random = rand();
+		memcpy(buf, &random, sizeof(random));
+		buf += sizeof(random);
+		nrem -= sizeof(random);
+	}
+
+	if (nrem) {
+		random = rand();
+		memcpy(buf, &random, nrem);
+	}
+
+	return 0;
+}
+
+static const struct dm_rng_ops sandbox_rng_ops = {
+	.read = sandbox_rng_read,
+};
+
+static const struct udevice_id sandbox_rng_match[] = {
+	{
+		.compatible = "sandbox,sandbox-rng",
+	},
+	{},
+};
+
+U_BOOT_DRIVER(sandbox_rng) = {
+	.name = "sandbox-rng",
+	.id = UCLASS_RNG,
+	.of_match = sandbox_rng_match,
+	.ops = &sandbox_rng_ops,
+};