summaryrefslogtreecommitdiffstats
path: root/drivers/char/hw_random/xiphera-trng.c
blob: 4af64f76c8d613189cca8714ee2b5d86651698e6 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
// 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/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;

	trng = devm_kzalloc(dev, sizeof(*trng), GFP_KERNEL);
	if (!trng)
		return -ENOMEM;

	trng->mem = devm_platform_ioremap_resource(pdev, 0);
	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;
	}

	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");