[PATCH 1/1] add turris-rwtm-rng from CZ.NIC rWTM Firmware

[Max Resch <resch.max@gmail.com>]

usable on all armada3700 devices with CZ.NIC firmware
compatible with devices with default firmware (does nothing)
based on Linux turris-mox-rwtm module

Signed-off-by: Max Resch <resch.max@gmail.com>
---

 drivers/rng/Kconfig           |   8 ++
 drivers/rng/Makefile          |   1 +
 drivers/rng/turris_rwtm_rng.c | 143 ++++++++++++++++++++++++++++++++++
 3 files changed, 152 insertions(+)
 create mode 100644 drivers/rng/turris_rwtm_rng.c

diff --git a/drivers/rng/Kconfig b/drivers/rng/Kconfig
index a89c899568..f5984a9ca0 100644
--- a/drivers/rng/Kconfig
+++ b/drivers/rng/Kconfig
@@ -105,4 +105,12 @@ config RNG_JH7110
 	help
 	  Enable True Random Number Generator in StarFive JH7110 SoCs.
 
+config RNG_TURRIS_RWTM
+	bool "Turris Mox TRNG in Secure Processor"
+	depends on DM_RNG && ARCH_MVEBU
+	help
+	  Use TRNG in Turris Mox Secure Processor Firmware. Can be used
+	  on other Armada-3700 devices (like EspressoBin) if Secure
+	  Firmware from CZ.NIC is used.
+
 endif
diff --git a/drivers/rng/Makefile b/drivers/rng/Makefile
index 7e64c4cdfc..ecae1a3da3 100644
--- a/drivers/rng/Makefile
+++ b/drivers/rng/Makefile
@@ -17,3 +17,4 @@ obj-$(CONFIG_RNG_SMCCC_TRNG) += smccc_trng.o
 obj-$(CONFIG_RNG_ARM_RNDR) += arm_rndr.o
 obj-$(CONFIG_TPM_RNG) += tpm_rng.o
 obj-$(CONFIG_RNG_JH7110) += jh7110_rng.o
+obj-$(CONFIG_RNG_TURRIS_RWTM) += turris_rwtm_rng.o
diff --git a/drivers/rng/turris_rwtm_rng.c b/drivers/rng/turris_rwtm_rng.c
new file mode 100644
index 0000000000..03e4fdfcaf
--- /dev/null
+++ b/drivers/rng/turris_rwtm_rng.c
@@ -0,0 +1,143 @@
+// SPDX-License-Identifier: GPL-2.0-or-later OR BSD-3-Clause
+/*
+ * Copyright (c) 2024, Max Resch
+ */
+
+#include <dm.h>
+#include <malloc.h>
+#include <rng.h>
+#include <asm/dma-mapping.h>
+#include <asm/types.h>
+#include <mach/mbox.h>
+
+#define DRIVER_NAME	"turris-rwtm-rng"
+
+/* size of enthropy ring buffer */
+#define RNG_BUFFER_SIZE	4096U
+
+struct turris_rwtm_rng_priv {
+	phys_addr_t buffer;
+	u16 pos;
+};
+
+static int turris_rwtm_rng_fill_enthropy(phys_addr_t enthropy, size_t size)
+{
+	int ret;
+	u32 args[] = { 1, (u32)enthropy, size };
+
+	/* flush data cache */
+	flush_dcache_range(enthropy, enthropy + size);
+
+	/*
+	 * get enthropy
+	 * args[0] = 1 copies BYTES array in args[1] of length args[2]
+	 */
+	ret = mbox_do_cmd(MBOX_CMD_GET_RANDOM, args, 3, NULL, 0);
+	if (ret < 0)
+		return ret;
+
+	/* invalidate data cache */
+	invalidate_dcache_range(enthropy, enthropy + size);
+
+	return 0;
+}
+
+static int turris_rwtm_rng_random_read(struct udevice *dev, void *data, size_t count)
+{
+	int ret;
+	struct turris_rwtm_rng_priv *priv;
+	phys_addr_t p;
+	size_t size, copied;
+
+	priv = (struct turris_rwtm_rng_priv *)dev_get_priv(dev);
+	p = priv->buffer;
+
+	/* copy to ring buffer, optimize RWTM access */
+	size = min_t(size_t, RNG_BUFFER_SIZE - priv->pos, count);
+	copied = 0;
+
+	while (count) {
+		memcpy(((u8 *)data) + copied, (void *)(p + priv->pos), size);
+		count -= size;
+		copied += size;
+		priv->pos += size;
+
+		if (priv->pos == RNG_BUFFER_SIZE) {
+			ret = turris_rwtm_rng_fill_enthropy(p, RNG_BUFFER_SIZE);
+			if (ret < 0)
+				return ret;
+			priv->pos = 0;
+		}
+	}
+
+	return 0;
+}
+
+static int turris_rwtm_rng_probe(struct udevice *dev)
+{
+	int ret;
+	struct turris_rwtm_rng_priv *priv;
+	u32 args[] = { 0 };
+
+	/*
+	 * check if the random command is supported
+	 * args[0] = 0 would copy 16 DWORDS to out but we ignore them
+	 */
+	ret = mbox_do_cmd(MBOX_CMD_GET_RANDOM, args, 1, NULL, 0);
+
+	if (ret < 0)
+		return ret;
+
+	/* allocate ring buffer */
+	priv = dev_get_priv(dev);
+	priv->buffer = 0;
+
+	/* address need to be aligned */
+	dma_alloc_coherent(RNG_BUFFER_SIZE, (unsigned long *)&priv->buffer);
+	if (!priv->buffer)
+		return -ENOMEM;
+
+	priv->pos = 0;
+	memset((void *)priv->buffer, 0, RNG_BUFFER_SIZE);
+
+	/* fill ring buffer with enthroy */
+	return turris_rwtm_rng_fill_enthropy(priv->buffer, RNG_BUFFER_SIZE);
+}
+
+static int turris_rwtm_rng_remove(struct udevice *dev)
+{
+	struct turris_rwtm_rng_priv *priv;
+
+	priv = dev_get_priv(dev);
+	if (!priv->buffer)
+		return 0;
+
+	dma_free_coherent((void *)priv->buffer);
+	priv->buffer = 0;
+
+	return 0;
+}
+
+static const struct dm_rng_ops turris_rwtm_rng_ops = {
+	.read = turris_rwtm_rng_random_read,
+};
+
+/*
+ * only Turris MOX firmware has the RNG but allow all probable devices to be
+ * probed the default firmware will just reject the probe
+ */
+static const struct udevice_id turris_rwtm_rng_match[] = {
+	{ .compatible = "cznic,turris-mox-rwtm" },
+	{ .compatible = "marvell,armada-3700-rwtm-firmware" },
+	{},
+};
+
+U_BOOT_DRIVER(turris_rwtm_rng) = {
+	.name	= DRIVER_NAME,
+	.id	= UCLASS_RNG,
+	.of_match = turris_rwtm_rng_match,
+	.ops	= &turris_rwtm_rng_ops,
+	.probe	= turris_rwtm_rng_probe,
+	.remove = turris_rwtm_rng_remove,
+	.priv_auto = sizeof(struct turris_rwtm_rng_priv),
+};
-- 
2.43.0