hwrng: add driver for MediaTek TRNG SMC

Add driver providing kernel-side support for the Random Number
Generator hardware found on Mediatek SoCs which have a driver in ARM
TrustedFirmware-A allowing Linux to read random numbers using a
non-standard vendor-defined Secure Monitor Call.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

Author: dangowrt

drivers/char/hw_random/Kconfig

@@ -477,6 +477,22 @@ config HW_RANDOM_MTK
 
 	  If unsure, say Y.
 
+config HW_RANDOM_MTK_V2
+	tristate "Mediatek Random Number Generator support (v2/SMC)"
+	depends on HW_RANDOM
+	depends on (ARM64 && ARCH_MEDIATEK) || COMPILE_TEST
+	default y
+	help
+	  This driver provides kernel-side support for the Random Number
+	  Generator hardware found on Mediatek SoCs which have a driver
+	  in ARM TrustedFirmware-A allowing Linux to read using a non-
+	  standard vendor-defined Secure Monitor Call.
+
+	  To compile this driver as a module, choose M here. the
+	  module will be called mtk-rng-v2.
+
+	  If unsure, say Y.
+
 config HW_RANDOM_S390
 	tristate "S390 True Random Number Generator support"
 	depends on S390

drivers/char/hw_random/Makefile

@@ -41,6 +41,7 @@ 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-$(CONFIG_HW_RANDOM_MTK_V2)	+= mtk-rng-v2.o
 obj-$(CONFIG_HW_RANDOM_S390) += s390-trng.o
 obj-$(CONFIG_HW_RANDOM_KEYSTONE) += ks-sa-rng.o
 obj-$(CONFIG_HW_RANDOM_OPTEE) += optee-rng.o

drivers/char/hw_random/mtk-rng-v2.c

@@ -0,0 +1,74 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Driver for Mediatek Hardware Random Number Generator (v2/SMCC)
+ *
+ * Copyright (C) 2023 Daniel Golle <daniel@makrotopia.org>
+ * based on patch from Mingming Su <Mingming.Su@mediatek.com>
+ */
+#define MTK_RNG_DEV KBUILD_MODNAME
+
+#include <linux/arm-smccc.h>
+#include <linux/err.h>
+#include <linux/hw_random.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_device.h>
+#include <linux/platform_device.h>
+#include <linux/soc/mediatek/mtk_sip_svc.h>
+
+#define MTK_SIP_KERNEL_GET_RND		MTK_SIP_SMC_CMD(0x550)
+
+static int mtk_rng_v2_read(struct hwrng *rng, void *buf, size_t max, bool wait)
+{
+	struct arm_smccc_res res;
+	int retval = 0;
+
+	while (max >= sizeof(u32)) {
+		arm_smccc_smc(MTK_SIP_KERNEL_GET_RND, 0, 0, 0, 0, 0, 0, 0,
+			      &res);
+		if (res.a0)
+			break;
+
+		*(u32 *)buf = res.a1;
+		retval += sizeof(u32);
+		buf += sizeof(u32);
+		max -= sizeof(u32);
+	}
+
+	return retval || !wait ? retval : -EIO;
+}
+
+static int mtk_rng_v2_probe(struct platform_device *pdev)
+{
+	struct hwrng *trng;
+
+	trng = devm_kzalloc(&pdev->dev, sizeof(*trng), GFP_KERNEL);
+	if (!trng)
+		return -ENOMEM;
+
+	trng->name = pdev->name;
+	trng->read = mtk_rng_v2_read;
+	trng->quality = 900;
+
+	return devm_hwrng_register(&pdev->dev, trng);
+}
+
+static const struct of_device_id mtk_rng_v2_match[] = {
+	{ .compatible = "mediatek,mt7981-rng" },
+	{},
+};
+MODULE_DEVICE_TABLE(of, mtk_rng_v2_match);
+
+static struct platform_driver mtk_rng_v2_driver = {
+	.probe          = mtk_rng_v2_probe,
+	.driver = {
+		.name = KBUILD_MODNAME,
+		.of_match_table = mtk_rng_v2_match,
+	},
+};
+module_platform_driver(mtk_rng_v2_driver);
+
+MODULE_DESCRIPTION("Mediatek Random Number Generator Driver (v2/SMC)");
+MODULE_AUTHOR("Daniel Golle <daniel@makrotopia.org>");
+MODULE_LICENSE("GPL");