1// SPDX-License-Identifier: GPL-2.0
2/* Copyright (C) 2020 Xiphera Ltd. */
3
4#include <linux/kernel.h>
5#include <linux/module.h>
6#include <linux/mod_devicetable.h>
7#include <linux/err.h>
8#include <linux/io.h>
9#include <linux/hw_random.h>
10#include <linux/of_device.h>
11#include <linux/platform_device.h>
12#include <linux/delay.h>
13
14#define CONTROL_REG			0x00000000
15#define STATUS_REG			0x00000004
16#define RAND_REG			0x00000000
17
18#define HOST_TO_TRNG_RESET		0x00000001
19#define HOST_TO_TRNG_RELEASE_RESET	0x00000002
20#define HOST_TO_TRNG_ENABLE		0x80000000
21#define HOST_TO_TRNG_ZEROIZE		0x80000004
22#define HOST_TO_TRNG_ACK_ZEROIZE	0x80000008
23#define HOST_TO_TRNG_READ		0x8000000F
24
25/* trng statuses */
26#define TRNG_ACK_RESET			0x000000AC
27#define TRNG_SUCCESSFUL_STARTUP		0x00000057
28#define TRNG_FAILED_STARTUP		0x000000FA
29#define TRNG_NEW_RAND_AVAILABLE		0x000000ED
30
31struct xiphera_trng {
32	void __iomem *mem;
33	struct hwrng rng;
34};
35
36static int xiphera_trng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
37{
38	struct xiphera_trng *trng = container_of(rng, struct xiphera_trng, rng);
39	int ret = 0;
40
41	while (max >= sizeof(u32)) {
42		/* check for data */
43		if (readl(trng->mem + STATUS_REG) == TRNG_NEW_RAND_AVAILABLE) {
44			*(u32 *)buf = readl(trng->mem + RAND_REG);
45			/*
46			 * Inform the trng of the read
47			 * and re-enable it to produce a new random number
48			 */
49			writel(HOST_TO_TRNG_READ, trng->mem + CONTROL_REG);
50			writel(HOST_TO_TRNG_ENABLE, trng->mem + CONTROL_REG);
51			ret += sizeof(u32);
52			buf += sizeof(u32);
53			max -= sizeof(u32);
54		} else {
55			break;
56		}
57	}
58	return ret;
59}
60
61static int xiphera_trng_probe(struct platform_device *pdev)
62{
63	int ret;
64	struct xiphera_trng *trng;
65	struct device *dev = &pdev->dev;
66	struct resource *res;
67
68	trng = devm_kzalloc(dev, sizeof(*trng), GFP_KERNEL);
69	if (!trng)
70		return -ENOMEM;
71
72	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
73	trng->mem = devm_ioremap_resource(dev, res);
74	if (IS_ERR(trng->mem))
75		return PTR_ERR(trng->mem);
76
77	/*
78	 * the trng needs to be reset first which might not happen in time,
79	 * hence we incorporate a small delay to ensure proper behaviour
80	 */
81	writel(HOST_TO_TRNG_RESET, trng->mem + CONTROL_REG);
82	usleep_range(100, 200);
83
84	if (readl(trng->mem + STATUS_REG) != TRNG_ACK_RESET) {
85		/*
86		 * there is a small chance the trng is just not ready yet,
87		 * so we try one more time. If the second time fails, we give up
88		 */
89		usleep_range(100, 200);
90		if (readl(trng->mem + STATUS_REG) != TRNG_ACK_RESET) {
91			dev_err(dev, "failed to reset the trng ip\n");
92			return -ENODEV;
93		}
94	}
95
96	/*
97	 * once again, to ensure proper behaviour we sleep
98	 * for a while after zeroizing the trng
99	 */
100	writel(HOST_TO_TRNG_RELEASE_RESET, trng->mem + CONTROL_REG);
101	writel(HOST_TO_TRNG_ENABLE, trng->mem + CONTROL_REG);
102	writel(HOST_TO_TRNG_ZEROIZE, trng->mem + CONTROL_REG);
103	msleep(20);
104
105	if (readl(trng->mem + STATUS_REG) != TRNG_SUCCESSFUL_STARTUP) {
106		/* diagnose the reason for the failure */
107		if (readl(trng->mem + STATUS_REG) == TRNG_FAILED_STARTUP) {
108			dev_err(dev, "trng ip startup-tests failed\n");
109			return -ENODEV;
110		}
111		dev_err(dev, "startup-tests yielded no response\n");
112		return -ENODEV;
113	}
114
115	writel(HOST_TO_TRNG_ACK_ZEROIZE, trng->mem + CONTROL_REG);
116
117	trng->rng.name = pdev->name;
118	trng->rng.read = xiphera_trng_read;
119	trng->rng.quality = 900;
120
121	ret = devm_hwrng_register(dev, &trng->rng);
122	if (ret) {
123		dev_err(dev, "failed to register rng device: %d\n", ret);
124		return ret;
125	}
126
127	platform_set_drvdata(pdev, trng);
128
129	return 0;
130}
131
132static const struct of_device_id xiphera_trng_of_match[] = {
133	{ .compatible = "xiphera,xip8001b-trng", },
134	{},
135};
136MODULE_DEVICE_TABLE(of, xiphera_trng_of_match);
137
138static struct platform_driver xiphera_trng_driver = {
139	.driver = {
140		.name = "xiphera-trng",
141		.of_match_table	= xiphera_trng_of_match,
142	},
143	.probe = xiphera_trng_probe,
144};
145
146module_platform_driver(xiphera_trng_driver);
147
148MODULE_LICENSE("GPL");
149MODULE_AUTHOR("Atte Tommiska");
150MODULE_DESCRIPTION("Xiphera FPGA-based true random number generator driver");
151