hwrng: xiphera-trng: add support for XIP8001B hwrng

Xiphera XIP8001B is an FPGA-based True Random Number Generator
Intellectual Property (IP) Core which can be instantiated in
multiple FPGA families. This driver adds Linux support for it through
the hwrng interface.

Signed-off-by: Atte Tommiska <atte.tommiska@xiphera.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/char/hw_random/Kconfig

@@ -512,6 +512,16 @@ config HW_RANDOM_CCTRNG
 	  will be called cctrng.
 	  If unsure, say 'N'.
 
+config HW_RANDOM_XIPHERA
+	tristate "Xiphera FPGA based True Random Number Generator support"
+	depends on HAS_IOMEM
+	help
+	  This driver provides kernel-side support for Xiphera True Random
+	  Number Generator Intellectual Property Core.
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called xiphera-trng.
+
 endif # HW_RANDOM
 
 config UML_RANDOM

drivers/char/hw_random/Makefile

@@ -44,3 +44,4 @@ obj-$(CONFIG_HW_RANDOM_KEYSTONE) += ks-sa-rng.o
 obj-$(CONFIG_HW_RANDOM_OPTEE) += optee-rng.o
 obj-$(CONFIG_HW_RANDOM_NPCM) += npcm-rng.o
 obj-$(CONFIG_HW_RANDOM_CCTRNG) += cctrng.o
+obj-$(CONFIG_HW_RANDOM_XIPHERA) += xiphera-trng.o

drivers/char/hw_random/xiphera-trng.c

@@ -0,0 +1,150 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (C) 2020 Xiphera Ltd. */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/mod_devicetable.h>
+#include <linux/err.h>
+#include <linux/io.h>
+#include <linux/hw_random.h>
+#include <linux/of_device.h>
+#include <linux/platform_device.h>
+#include <linux/delay.h>
+
+#define CONTROL_REG			0x00000000
+#define STATUS_REG			0x00000004
+#define RAND_REG			0x00000000
+
+#define HOST_TO_TRNG_RESET		0x00000001
+#define HOST_TO_TRNG_RELEASE_RESET	0x00000002
+#define HOST_TO_TRNG_ENABLE		0x80000000
+#define HOST_TO_TRNG_ZEROIZE		0x80000004
+#define HOST_TO_TRNG_ACK_ZEROIZE	0x80000008
+#define HOST_TO_TRNG_READ		0x8000000F
+
+/* trng statuses */
+#define TRNG_ACK_RESET			0x000000AC
+#define TRNG_SUCCESSFUL_STARTUP		0x00000057
+#define TRNG_FAILED_STARTUP		0x000000FA
+#define TRNG_NEW_RAND_AVAILABLE		0x000000ED
+
+struct xiphera_trng {
+	void __iomem *mem;
+	struct hwrng rng;
+};
+
+static int xiphera_trng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
+{
+	struct xiphera_trng *trng = container_of(rng, struct xiphera_trng, rng);
+	int ret = 0;
+
+	while (max >= sizeof(u32)) {
+		/* check for data */
+		if (readl(trng->mem + STATUS_REG) == TRNG_NEW_RAND_AVAILABLE) {
+			*(u32 *)buf = readl(trng->mem + RAND_REG);
+			/*
+			 * Inform the trng of the read
+			 * and re-enable it to produce a new random number
+			 */
+			writel(HOST_TO_TRNG_READ, trng->mem + CONTROL_REG);
+			writel(HOST_TO_TRNG_ENABLE, trng->mem + CONTROL_REG);
+			ret += sizeof(u32);
+			buf += sizeof(u32);
+			max -= sizeof(u32);
+		} else {
+			break;
+		}
+	}
+	return ret;
+}
+
+static int xiphera_trng_probe(struct platform_device *pdev)
+{
+	int ret;
+	struct xiphera_trng *trng;
+	struct device *dev = &pdev->dev;
+	struct resource *res;
+
+	trng = devm_kzalloc(dev, sizeof(*trng), GFP_KERNEL);
+	if (!trng)
+		return -ENOMEM;
+
+	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	trng->mem = devm_ioremap_resource(dev, res);
+	if (IS_ERR(trng->mem))
+		return PTR_ERR(trng->mem);
+
+	/*
+	 * the trng needs to be reset first which might not happen in time,
+	 * hence we incorporate a small delay to ensure proper behaviour
+	 */
+	writel(HOST_TO_TRNG_RESET, trng->mem + CONTROL_REG);
+	usleep_range(100, 200);
+
+	if (readl(trng->mem + STATUS_REG) != TRNG_ACK_RESET) {
+		/*
+		 * there is a small chance the trng is just not ready yet,
+		 * so we try one more time. If the second time fails, we give up
+		 */
+		usleep_range(100, 200);
+		if (readl(trng->mem + STATUS_REG) != TRNG_ACK_RESET) {
+			dev_err(dev, "failed to reset the trng ip\n");
+			return -ENODEV;
+		}
+	}
+
+	/*
+	 * once again, to ensure proper behaviour we sleep
+	 * for a while after zeroizing the trng
+	 */
+	writel(HOST_TO_TRNG_RELEASE_RESET, trng->mem + CONTROL_REG);
+	writel(HOST_TO_TRNG_ENABLE, trng->mem + CONTROL_REG);
+	writel(HOST_TO_TRNG_ZEROIZE, trng->mem + CONTROL_REG);
+	msleep(20);
+
+	if (readl(trng->mem + STATUS_REG) != TRNG_SUCCESSFUL_STARTUP) {
+		/* diagnose the reason for the failure */
+		if (readl(trng->mem + STATUS_REG) == TRNG_FAILED_STARTUP) {
+			dev_err(dev, "trng ip startup-tests failed\n");
+			return -ENODEV;
+		}
+		dev_err(dev, "startup-tests yielded no response\n");
+		return -ENODEV;
+	}
+
+	writel(HOST_TO_TRNG_ACK_ZEROIZE, trng->mem + CONTROL_REG);
+
+	trng->rng.name = pdev->name;
+	trng->rng.read = xiphera_trng_read;
+	trng->rng.quality = 900;
+
+	ret = devm_hwrng_register(dev, &trng->rng);
+	if (ret) {
+		dev_err(dev, "failed to register rng device: %d\n", ret);
+		return ret;
+	}
+
+	platform_set_drvdata(pdev, trng);
+
+	return 0;
+}
+
+static const struct of_device_id xiphera_trng_of_match[] = {
+	{ .compatible = "xiphera,xip8001b-trng", },
+	{},
+};
+MODULE_DEVICE_TABLE(of, xiphera_trng_of_match);
+
+static struct platform_driver xiphera_trng_driver = {
+	.driver = {
+		.name = "xiphera-trng",
+		.of_match_table	= xiphera_trng_of_match,
+	},
+	.probe = xiphera_trng_probe,
+};
+
+module_platform_driver(xiphera_trng_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Atte Tommiska");
+MODULE_DESCRIPTION("Xiphera FPGA-based true random number generator driver");