hwrng: bcm74110 - Add Broadcom BCM74110 RNG driver

Add a driver for the random number generator present on the Broadcom
BCM74110 SoC.

Signed-off-by: Markus Mayer <mmayer@broadcom.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/char/hw_random/Kconfig

@@ -112,6 +112,19 @@ config HW_RANDOM_BCM2835
 
 	  If unsure, say Y.
 
+config HW_RANDOM_BCM74110
+	tristate "Broadcom BCM74110 Random Number Generator support"
+	depends on ARCH_BRCMSTB || COMPILE_TEST
+	default HW_RANDOM
+	help
+	  This driver provides kernel-side support for the Random Number
+	  Generator hardware found on the Broadcom BCM74110 SoCs.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called bcm74110-rng
+
+	  If unsure, say Y.
+
 config HW_RANDOM_IPROC_RNG200
 	tristate "Broadcom iProc/STB RNG200 support"
 	depends on ARCH_BCM_IPROC || ARCH_BCM2835 || ARCH_BCMBCA || ARCH_BRCMSTB || COMPILE_TEST

drivers/char/hw_random/Makefile

@@ -32,6 +32,7 @@ obj-$(CONFIG_HW_RANDOM_POWERNV) += powernv-rng.o
 obj-$(CONFIG_HW_RANDOM_HISI)	+= hisi-rng.o
 obj-$(CONFIG_HW_RANDOM_HISTB) += histb-rng.o
 obj-$(CONFIG_HW_RANDOM_BCM2835) += bcm2835-rng.o
+obj-$(CONFIG_HW_RANDOM_BCM74110) += bcm74110-rng.o
 obj-$(CONFIG_HW_RANDOM_IPROC_RNG200) += iproc-rng200.o
 obj-$(CONFIG_HW_RANDOM_ST) += st-rng.o
 obj-$(CONFIG_HW_RANDOM_XGENE) += xgene-rng.o

drivers/char/hw_random/bcm74110-rng.c

@@ -0,0 +1,125 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2024 Broadcom
+ */
+
+#define pr_fmt(fmt)	KBUILD_MODNAME ": " fmt
+
+#include <linux/module.h>
+#include <linux/mod_devicetable.h>
+#include <linux/kernel.h>
+#include <linux/io.h>
+#include <linux/delay.h>
+#include <linux/platform_device.h>
+#include <linux/random.h>
+#include <linux/hw_random.h>
+
+#define HOST_REV_ID		0x00
+#define HOST_FIFO_DEPTH		0x04
+#define HOST_FIFO_COUNT		0x08
+#define HOST_FIFO_THRESHOLD	0x0c
+#define HOST_FIFO_DATA		0x10
+
+#define HOST_FIFO_COUNT_MASK		0xffff
+
+/* Delay range in microseconds */
+#define FIFO_DELAY_MIN_US		3
+#define FIFO_DELAY_MAX_US		7
+#define FIFO_DELAY_MAX_COUNT		10
+
+struct bcm74110_priv {
+	void __iomem *base;
+};
+
+static inline int bcm74110_rng_fifo_count(void __iomem *mem)
+{
+	return readl_relaxed(mem) & HOST_FIFO_COUNT_MASK;
+}
+
+static int bcm74110_rng_read(struct hwrng *rng, void *buf, size_t max,
+			bool wait)
+{
+	struct bcm74110_priv *priv = (struct bcm74110_priv *)rng->priv;
+	void __iomem *fc_addr = priv->base + HOST_FIFO_COUNT;
+	void __iomem *fd_addr = priv->base + HOST_FIFO_DATA;
+	unsigned underrun_count = 0;
+	u32 max_words = max / sizeof(u32);
+	u32 num_words;
+	unsigned i;
+
+	/*
+	 * We need to check how many words are available in the RNG FIFO. If
+	 * there aren't any, we need to wait for some to become available.
+	 */
+	while ((num_words = bcm74110_rng_fifo_count(fc_addr)) == 0) {
+		if (!wait)
+			return 0;
+		/*
+		 * As a precaution, limit how long we wait. If the FIFO doesn't
+		 * refill within the allotted time, return 0 (=no data) to the
+		 * caller.
+		 */
+		if (likely(underrun_count < FIFO_DELAY_MAX_COUNT))
+			usleep_range(FIFO_DELAY_MIN_US, FIFO_DELAY_MAX_US);
+		else
+			return 0;
+		underrun_count++;
+	}
+	if (num_words > max_words)
+		num_words = max_words;
+
+	/* Bail early if we run out of random numbers unexpectedly */
+	for (i = 0; i < num_words && bcm74110_rng_fifo_count(fc_addr) > 0; i++)
+		((u32 *)buf)[i] = readl_relaxed(fd_addr);
+
+	return i * sizeof(u32);
+}
+
+static struct hwrng bcm74110_hwrng = {
+	.read = bcm74110_rng_read,
+};
+
+static int bcm74110_rng_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct bcm74110_priv *priv;
+	int rc;
+
+	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	bcm74110_hwrng.name = pdev->name;
+	bcm74110_hwrng.priv = (unsigned long)priv;
+
+	priv->base = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(priv->base))
+		return PTR_ERR(priv->base);
+
+	rc = devm_hwrng_register(dev, &bcm74110_hwrng);
+	if (rc)
+		dev_err(dev, "hwrng registration failed (%d)\n", rc);
+	else
+		dev_info(dev, "hwrng registered\n");
+
+	return rc;
+}
+
+static const struct of_device_id bcm74110_rng_match[] = {
+	{ .compatible	= "brcm,bcm74110-rng", },
+	{},
+};
+MODULE_DEVICE_TABLE(of, bcm74110_rng_match);
+
+static struct platform_driver bcm74110_rng_driver = {
+	.driver = {
+		.name = KBUILD_MODNAME,
+		.of_match_table = bcm74110_rng_match,
+	},
+	.probe	= bcm74110_rng_probe,
+};
+module_platform_driver(bcm74110_rng_driver);
+
+MODULE_AUTHOR("Markus Mayer <mmayer@broadcom.com>");
+MODULE_DESCRIPTION("BCM 74110 Random Number Generator (RNG) driver");
+MODULE_LICENSE("GPL v2");