1 // SPDX-License-Identifier: GPL-2.0-or-later OR MIT
2 /*
3  * Copyright (c) 2023 David Yang
4  */
5 
6 #include <linux/err.h>
7 #include <linux/hw_random.h>
8 #include <linux/io.h>
9 #include <linux/iopoll.h>
10 #include <linux/kernel.h>
11 #include <linux/mod_devicetable.h>
12 #include <linux/module.h>
13 #include <linux/platform_device.h>
14 
15 #define RNG_CTRL		0x0
16 #define  RNG_SOURCE			GENMASK(1, 0)
17 #define  DROP_ENABLE			BIT(5)
18 #define  POST_PROCESS_ENABLE		BIT(7)
19 #define  POST_PROCESS_DEPTH		GENMASK(15, 8)
20 #define RNG_NUMBER		0x4
21 #define RNG_STAT		0x8
22 #define  DATA_COUNT			GENMASK(2, 0)	/* max 4 */
23 
24 struct histb_rng_priv {
25 	struct hwrng rng;
26 	void __iomem *base;
27 };
28 
29 /*
30  * Observed:
31  * depth = 1 -> ~1ms
32  * depth = 255 -> ~16ms
33  */
34 static int histb_rng_wait(void __iomem *base)
35 {
36 	u32 val;
37 
38 	return readl_relaxed_poll_timeout(base + RNG_STAT, val,
39 					  val & DATA_COUNT, 1000, 30 * 1000);
40 }
41 
42 static void histb_rng_init(void __iomem *base, unsigned int depth)
43 {
44 	u32 val;
45 
46 	val = readl_relaxed(base + RNG_CTRL);
47 
48 	val &= ~RNG_SOURCE;
49 	val |= 2;
50 
51 	val &= ~POST_PROCESS_DEPTH;
52 	val |= min(depth, 0xffu) << 8;
53 
54 	val |= POST_PROCESS_ENABLE;
55 	val |= DROP_ENABLE;
56 
57 	writel_relaxed(val, base + RNG_CTRL);
58 }
59 
60 static int histb_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
61 {
62 	struct histb_rng_priv *priv = container_of(rng, typeof(*priv), rng);
63 	void __iomem *base = priv->base;
64 
65 	for (int i = 0; i < max; i += sizeof(u32)) {
66 		if (!(readl_relaxed(base + RNG_STAT) & DATA_COUNT)) {
67 			if (!wait)
68 				return i;
69 			if (histb_rng_wait(base)) {
70 				pr_err("failed to generate random number, generated %d\n",
71 				       i);
72 				return i ? i : -ETIMEDOUT;
73 			}
74 		}
75 		*(u32 *) (data + i) = readl_relaxed(base + RNG_NUMBER);
76 	}
77 
78 	return max;
79 }
80 
81 static unsigned int histb_rng_get_depth(void __iomem *base)
82 {
83 	return (readl_relaxed(base + RNG_CTRL) & POST_PROCESS_DEPTH) >> 8;
84 }
85 
86 static ssize_t
87 depth_show(struct device *dev, struct device_attribute *attr, char *buf)
88 {
89 	struct histb_rng_priv *priv = dev_get_drvdata(dev);
90 	void __iomem *base = priv->base;
91 
92 	return sprintf(buf, "%d\n", histb_rng_get_depth(base));
93 }
94 
95 static ssize_t
96 depth_store(struct device *dev, struct device_attribute *attr,
97 	    const char *buf, size_t count)
98 {
99 	struct histb_rng_priv *priv = dev_get_drvdata(dev);
100 	void __iomem *base = priv->base;
101 	unsigned int depth;
102 
103 	if (kstrtouint(buf, 0, &depth))
104 		return -ERANGE;
105 
106 	histb_rng_init(base, depth);
107 	return count;
108 }
109 
110 static DEVICE_ATTR_RW(depth);
111 
112 static struct attribute *histb_rng_attrs[] = {
113 	&dev_attr_depth.attr,
114 	NULL,
115 };
116 
117 ATTRIBUTE_GROUPS(histb_rng);
118 
119 static int histb_rng_probe(struct platform_device *pdev)
120 {
121 	struct device *dev = &pdev->dev;
122 	struct histb_rng_priv *priv;
123 	void __iomem *base;
124 	int ret;
125 
126 	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
127 	if (!priv)
128 		return -ENOMEM;
129 
130 	base = devm_platform_ioremap_resource(pdev, 0);
131 	if (IS_ERR(base))
132 		return PTR_ERR(base);
133 
134 	histb_rng_init(base, 144);
135 	if (histb_rng_wait(base)) {
136 		dev_err(dev, "cannot bring up device\n");
137 		return -ENODEV;
138 	}
139 
140 	priv->base = base;
141 	priv->rng.name = pdev->name;
142 	priv->rng.read = histb_rng_read;
143 	ret = devm_hwrng_register(dev, &priv->rng);
144 	if (ret) {
145 		dev_err(dev, "failed to register hwrng: %d\n", ret);
146 		return ret;
147 	}
148 
149 	platform_set_drvdata(pdev, priv);
150 	dev_set_drvdata(dev, priv);
151 	return 0;
152 }
153 
154 static const struct of_device_id histb_rng_of_match[] = {
155 	{ .compatible = "hisilicon,histb-rng", },
156 	{ }
157 };
158 MODULE_DEVICE_TABLE(of, histb_rng_of_match);
159 
160 static struct platform_driver histb_rng_driver = {
161 	.probe = histb_rng_probe,
162 	.driver = {
163 		.name = "histb-rng",
164 		.of_match_table = histb_rng_of_match,
165 		.dev_groups = histb_rng_groups,
166 	},
167 };
168 
169 module_platform_driver(histb_rng_driver);
170 
171 MODULE_DESCRIPTION("Hisilicon STB random number generator driver");
172 MODULE_LICENSE("Dual MIT/GPL");
173 MODULE_AUTHOR("David Yang <mmyangfl@gmail.com>");
174