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