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
31 struct xiphera_trng {
32 void __iomem *mem;
33 struct hwrng rng;
34 };
35
xiphera_trng_read(struct hwrng * rng,void * buf,size_t max,bool wait)36 static 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
xiphera_trng_probe(struct platform_device * pdev)61 static int xiphera_trng_probe(struct platform_device *pdev)
62 {
63 int ret;
64 struct xiphera_trng *trng;
65 struct device *dev = &pdev->dev;
66
67 trng = devm_kzalloc(dev, sizeof(*trng), GFP_KERNEL);
68 if (!trng)
69 return -ENOMEM;
70
71 trng->mem = devm_platform_ioremap_resource(pdev, 0);
72 if (IS_ERR(trng->mem))
73 return PTR_ERR(trng->mem);
74
75 /*
76 * the trng needs to be reset first which might not happen in time,
77 * hence we incorporate a small delay to ensure proper behaviour
78 */
79 writel(HOST_TO_TRNG_RESET, trng->mem + CONTROL_REG);
80 usleep_range(100, 200);
81
82 if (readl(trng->mem + STATUS_REG) != TRNG_ACK_RESET) {
83 /*
84 * there is a small chance the trng is just not ready yet,
85 * so we try one more time. If the second time fails, we give up
86 */
87 usleep_range(100, 200);
88 if (readl(trng->mem + STATUS_REG) != TRNG_ACK_RESET) {
89 dev_err(dev, "failed to reset the trng ip\n");
90 return -ENODEV;
91 }
92 }
93
94 /*
95 * once again, to ensure proper behaviour we sleep
96 * for a while after zeroizing the trng
97 */
98 writel(HOST_TO_TRNG_RELEASE_RESET, trng->mem + CONTROL_REG);
99 writel(HOST_TO_TRNG_ENABLE, trng->mem + CONTROL_REG);
100 writel(HOST_TO_TRNG_ZEROIZE, trng->mem + CONTROL_REG);
101 msleep(20);
102
103 if (readl(trng->mem + STATUS_REG) != TRNG_SUCCESSFUL_STARTUP) {
104 /* diagnose the reason for the failure */
105 if (readl(trng->mem + STATUS_REG) == TRNG_FAILED_STARTUP) {
106 dev_err(dev, "trng ip startup-tests failed\n");
107 return -ENODEV;
108 }
109 dev_err(dev, "startup-tests yielded no response\n");
110 return -ENODEV;
111 }
112
113 writel(HOST_TO_TRNG_ACK_ZEROIZE, trng->mem + CONTROL_REG);
114
115 trng->rng.name = pdev->name;
116 trng->rng.read = xiphera_trng_read;
117 trng->rng.quality = 900;
118
119 ret = devm_hwrng_register(dev, &trng->rng);
120 if (ret) {
121 dev_err(dev, "failed to register rng device: %d\n", ret);
122 return ret;
123 }
124
125 platform_set_drvdata(pdev, trng);
126
127 return 0;
128 }
129
130 static const struct of_device_id xiphera_trng_of_match[] = {
131 { .compatible = "xiphera,xip8001b-trng", },
132 {},
133 };
134 MODULE_DEVICE_TABLE(of, xiphera_trng_of_match);
135
136 static struct platform_driver xiphera_trng_driver = {
137 .driver = {
138 .name = "xiphera-trng",
139 .of_match_table = xiphera_trng_of_match,
140 },
141 .probe = xiphera_trng_probe,
142 };
143
144 module_platform_driver(xiphera_trng_driver);
145
146 MODULE_LICENSE("GPL");
147 MODULE_AUTHOR("Atte Tommiska");
148 MODULE_DESCRIPTION("Xiphera FPGA-based true random number generator driver");
149