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 
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 
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