[PATCH v5 3/3] hwrng: add mtk-sec-rng driver

[Neal Liu]

For MediaTek SoCs on ARMv8 with TrustZone enabled, peripherals like
entropy sources is not accessible from normal world (linux) and
rather accessible from secure world (ATF/TEE) only. This driver aims
to provide a generic interface to ATF rng service.

Signed-off-by: Neal Liu <neal.liu@xxxxxxxxxxxx>
---
 drivers/char/hw_random/Kconfig       |   16 ++++++
 drivers/char/hw_random/Makefile      |    1 +
 drivers/char/hw_random/mtk-sec-rng.c |  103 ++++++++++++++++++++++++++++++++++
 3 files changed, 120 insertions(+)
 create mode 100644 drivers/char/hw_random/mtk-sec-rng.c

diff --git a/drivers/char/hw_random/Kconfig b/drivers/char/hw_random/Kconfig
index 25a7d8f..f08c852 100644
--- a/drivers/char/hw_random/Kconfig
+++ b/drivers/char/hw_random/Kconfig
@@ -398,6 +398,22 @@ config HW_RANDOM_MTK
 
 	  If unsure, say Y.
 
+config HW_RANDOM_MTK_SEC
+	tristate "MediaTek Security Random Number Generator support"
+	depends on HW_RANDOM
+	depends on ARCH_MEDIATEK || COMPILE_TEST
+	default HW_RANDOM
+	  help
+	  This driver provides kernel-side support for the Random Number
+	  Generator hardware found on MediaTek SoCs. The difference with
+	  mtk-rng is the Random Number Generator hardware is secure
+	  access only.
+
+	  To compile this driver as a module, choose M here. the
+	  module will be called mtk-sec-rng.
+
+	  If unsure, say Y.
+
 config HW_RANDOM_S390
 	tristate "S390 True Random Number Generator support"
 	depends on S390
diff --git a/drivers/char/hw_random/Makefile b/drivers/char/hw_random/Makefile
index 7c9ef4a..bee5412 100644
--- a/drivers/char/hw_random/Makefile
+++ b/drivers/char/hw_random/Makefile
@@ -36,6 +36,7 @@ obj-$(CONFIG_HW_RANDOM_PIC32) += pic32-rng.o
 obj-$(CONFIG_HW_RANDOM_MESON) += meson-rng.o
 obj-$(CONFIG_HW_RANDOM_CAVIUM) += cavium-rng.o cavium-rng-vf.o
 obj-$(CONFIG_HW_RANDOM_MTK)	+= mtk-rng.o
+obj-$(CONFIG_HW_RANDOM_MTK_SEC)	+= mtk-sec-rng.o
 obj-$(CONFIG_HW_RANDOM_S390) += s390-trng.o
 obj-$(CONFIG_HW_RANDOM_KEYSTONE) += ks-sa-rng.o
 obj-$(CONFIG_HW_RANDOM_OPTEE) += optee-rng.o
diff --git a/drivers/char/hw_random/mtk-sec-rng.c b/drivers/char/hw_random/mtk-sec-rng.c
new file mode 100644
index 0000000..69ddeca
--- /dev/null
+++ b/drivers/char/hw_random/mtk-sec-rng.c
@@ -0,0 +1,103 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2019 MediaTek Inc.
+ */
+
+#include <linux/arm-smccc.h>
+#include <linux/hw_random.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/soc/mediatek/mtk_sip_svc.h>
+
+#define MTK_SEC_RNG_MAGIC	0x74726e67
+#define SMC_RET_NUM		4
+#define MTK_SEC_RND_SIZE	(sizeof(u32) * SMC_RET_NUM)
+
+static void mtk_sec_get_rnd(uint32_t *val)
+{
+	struct arm_smccc_res res;
+
+	arm_smccc_smc(MTK_SIP_KERNEL_GET_RND,
+		      MTK_SEC_RNG_MAGIC, 0, 0, 0, 0, 0, 0, &res);
+
+	val[0] = res.a0;
+	val[1] = res.a1;
+	val[2] = res.a2;
+	val[3] = res.a3;
+}
+
+static int mtk_sec_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
+{
+	u32 val[4] = {0};
+	int retval = 0;
+	int i;
+
+	while (max >= MTK_SEC_RND_SIZE) {
+		mtk_sec_get_rnd(val);
+
+		for (i = 0; i < SMC_RET_NUM; i++) {
+			*(u32 *)buf = val[i];
+			buf += sizeof(u32);
+		}
+
+		retval += MTK_SEC_RND_SIZE;
+		max -= MTK_SEC_RND_SIZE;
+	}
+
+	return retval;
+}
+
+static struct hwrng mtk_sec_rng = {
+	.name = "mtk_sec_rng",
+	.read = mtk_sec_rng_read,
+	.quality = 900,
+};
+
+static int mtk_sec_rng_probe(void)
+{
+	int ret;
+
+	ret = hwrng_register(&mtk_sec_rng);
+	if (ret) {
+		pr_err("Failed to register rng device: %d\n", ret);
+		return ret;
+	}
+
+	return 0;
+}
+
+static int __init mtk_sec_rng_driver_init(void)
+{
+	struct device_node *fw_np;
+	struct device_node *np;
+	const char *method;
+
+	fw_np = of_find_node_by_name(NULL, "firmware");
+	if (!fw_np)
+		return -ENODEV;
+
+	np = of_find_compatible_node(fw_np, NULL, "mediatek,mtk-sec-rng");
+	if (!np)
+		return -ENODEV;
+
+	if (of_property_read_string(np, "method", &method))
+		return -ENXIO;
+
+	if (strncmp("smc", method, strlen("smc")))
+		return -EINVAL;
+
+	return mtk_sec_rng_probe();
+}
+
+static void __exit mtk_sec_rng_driver_exit(void)
+{
+	hwrng_unregister(&mtk_sec_rng);
+}
+
+module_init(mtk_sec_rng_driver_init);
+module_exit(mtk_sec_rng_driver_exit);
+
+MODULE_DESCRIPTION("MediaTek Security Random Number Generator Driver");
+MODULE_AUTHOR("Neal Liu <neal.liu@xxxxxxxxxxxx>");
+MODULE_LICENSE("GPL");
-- 
1.7.9.5