hw_random: add tegra hw_random driver

Add Tegra HW random driver to support /dev/hwrng. This driver calls into
the tegra rng using the kernel crypto framework APIs.

Bug 3326341

Change-Id: I628632d52d24c29ea55eb5f6e2b86627b91594f6
Signed-off-by: Harinarayan Bhatta <hbhatta@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/c/linux-nvidia/+/2569911
Reviewed-by: Dmitry Pervushin <dpervushin@nvidia.com>
Reviewed-by: Rohit Upadhyay <rupadhyay@nvidia.com>
Reviewed-by: mobile promotions <svcmobile_promotions@nvidia.com>
GVS: Gerrit_Virtual_Submit
Tested-by: mobile promotions <svcmobile_promotions@nvidia.com>

3 files changed, 101 insertions, 0 deletions

diff --git a/drivers/char/hw_random/Kconfig b/drivers/char/hw_random/Kconfig
new file mode 100644
index 000000000..279c3df3b
--- /dev/null
+++ b/drivers/char/hw_random/Kconfig
@@ -0,0 +1,18 @@
+#
+# Hardware Random Number Generator (RNG) configuration
+#
+
+if HW_RANDOM
+
+config HW_RANDOM_TEGRA
+       tristate "Tegra Random Number Generator support"
+       depends on HW_RANDOM && CRYPTO_DEV_TEGRA_VIRTUAL_SE_INTERFACE
+       default HW_RANDOM
+       ---help---
+         This driver provides kernel-side support for the Random Number
+         Generator hardware found on tegra.
+
+         If unsure, say N.
+
+endif # HW_RANDOM
+
diff --git a/drivers/char/hw_random/Makefile b/drivers/char/hw_random/Makefile
new file mode 100644
index 000000000..449eadab7
--- /dev/null
+++ b/drivers/char/hw_random/Makefile
@@ -0,0 +1,5 @@
+#
+# Makefile for HW Random Number Generator (RNG) device drivers.
+#
+
+obj-$(CONFIG_HW_RANDOM_TEGRA) += tegra-rng.o
diff --git a/drivers/char/hw_random/tegra-rng.c b/drivers/char/hw_random/tegra-rng.c
new file mode 100644
index 000000000..10d68dae2
--- /dev/null
+++ b/drivers/char/hw_random/tegra-rng.c
@@ -0,0 +1,78 @@
+/*
+ * drivers/char/hw_random/tegra-rng.c
+ *
+ * hwrng dev node for NVIDIA tegra rng hardware
+ *
+ * Copyright (c) 2021, NVIDIA Corporation. All Rights Reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ */
+#include <linux/module.h>
+#include <linux/time.h>
+#include <linux/delay.h>
+#include <linux/hw_random.h>
+#include <crypto/rng.h>
+
+#define MODULE_NAME "tegra-rng"
+#define RETRY_TIMEOUT_SECS      2
+
+static int tegra_rng_read(struct hwrng *h, void *data, size_t max, bool wait)
+{
+        int ret;
+        struct crypto_rng *rng;
+        unsigned long t;
+
+        if (!wait)
+                return 0;
+
+        rng = crypto_alloc_rng("rng1-elp-tegra",
+                        CRYPTO_ALG_TYPE_RNG, 0);
+        if (IS_ERR(rng)) {
+                pr_err("crypto_alloc_rng(rng1-elp-tegra) failed: %ld\n",
+                                PTR_ERR(rng));
+                return PTR_ERR(rng);
+        }
+        t = get_seconds();
+        do {
+                ret = crypto_rng_get_bytes(rng, data, max);
+                if (ret != -EAGAIN)
+                        break;
+                msleep_interruptible(20);
+        } while ((get_seconds() - t) <= RETRY_TIMEOUT_SECS);
+
+        /* crypto_rng_get_bytes returns 0 upon success */
+        if (ret == 0)
+                ret = max;
+
+        crypto_free_rng(rng);
+        return ret;
+}
+
+static struct hwrng tegra_rng = {
+        .name = MODULE_NAME,
+        .read = tegra_rng_read,
+};
+
+static int __init tegra_rng_init(void)
+{
+        return hwrng_register(&tegra_rng);
+}
+module_init(tegra_rng_init);
+
+static void __exit tegra_rng_exit(void)
+{
+        hwrng_unregister(&tegra_rng);
+}
+module_exit(tegra_rng_exit);
+
+MODULE_DESCRIPTION("RNG driver for Tegra devices");
+MODULE_AUTHOR("Harinarayan Bhatta <hbhatta@nvidia.com>");
+MODULE_LICENSE("GPL v2");