[PATCH v5 5/8] sandbox: rng: Add a random number generator(rng) driver

[Sughosh Ganu]

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 at linaro.org>
Reviewed-by: Patrice Chotard <patrice.chotard at st.com>
---
Changes since V4:
* Return number of bytes read on a successful read, and a -ve value on
  error.
* Modify the logic of sandbox_rng_read function to use rand and srand
  functions to return random data, based on feedback from Heinrich
  Schuchardt.

 arch/sandbox/dts/test.dts |  4 ++++
 drivers/rng/Kconfig       |  8 +++++++
 drivers/rng/Makefile      |  1 +
 drivers/rng/sandbox_rng.c | 56 +++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 69 insertions(+)
 create mode 100644 drivers/rng/sandbox_rng.c

diff --git a/arch/sandbox/dts/test.dts b/arch/sandbox/dts/test.dts
index fdb08f2..2c85540 100644
--- a/arch/sandbox/dts/test.dts
+++ b/arch/sandbox/dts/test.dts
@@ -599,6 +599,10 @@
 		reset-names = "other", "test";
 	};
 
+	rng at 0 {
+		compatible = "sandbox,sandbox-rng";
+	};
+
 	rproc_1: rproc at 1 {
 		compatible = "sandbox,test-processor";
 		remoteproc-name = "remoteproc-test-dev1";
diff --git a/drivers/rng/Kconfig b/drivers/rng/Kconfig
index c9c4751..35a3bd1 100644
--- a/drivers/rng/Kconfig
+++ b/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
diff --git a/drivers/rng/Makefile b/drivers/rng/Makefile
index 699beb3..3517005 100644
--- a/drivers/rng/Makefile
+++ b/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
diff --git a/drivers/rng/sandbox_rng.c b/drivers/rng/sandbox_rng.c
new file mode 100644
index 0000000..5de1799
--- /dev/null
+++ b/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)
+{
+	int nbytes;
+	unsigned int i, seed;
+	unsigned int *buf = data;
+	size_t nrem, nloops;
+
+	/*
+	 * Only INT_MAX number of bytes can be returned. If more
+	 * bytes need to be read, the caller must do it in a loop.
+	 */
+	if (len > INT_MAX)
+		len = INT_MAX;
+
+	nbytes = len;
+	nloops = len / sizeof(unsigned int);
+	seed = get_timer(0) ^ rand();
+	srand(seed);
+
+	for (i = 0, nrem = len; i < nloops; i++, nrem -= sizeof(unsigned int))
+		*buf++ = rand();
+
+	seed = rand();
+	memcpy(buf, &seed, nrem);
+
+	return nbytes;
+}
+
+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,
+};
-- 
2.7.4