1 // SPDX-License-Identifier: GPL-2.0
2 // Copyright (c) 2020 Silex Insight
3 
4 #include <linux/delay.h>
5 #include <linux/hw_random.h>
6 #include <linux/io.h>
7 #include <linux/iopoll.h>
8 #include <linux/kernel.h>
9 #include <linux/mod_devicetable.h>
10 #include <linux/module.h>
11 #include <linux/platform_device.h>
12 #include <linux/workqueue.h>
13 
14 #define BA431_RESET_DELAY			1 /* usec */
15 #define BA431_RESET_READ_STATUS_TIMEOUT		1000 /* usec */
16 #define BA431_RESET_READ_STATUS_INTERVAL	10 /* usec */
17 #define BA431_READ_RETRY_INTERVAL		1 /* usec */
18 
19 #define BA431_REG_CTRL				0x00
20 #define BA431_REG_FIFO_LEVEL			0x04
21 #define BA431_REG_STATUS			0x30
22 #define BA431_REG_FIFODATA			0x80
23 
24 #define BA431_CTRL_ENABLE			BIT(0)
25 #define BA431_CTRL_SOFTRESET			BIT(8)
26 
27 #define BA431_STATUS_STATE_MASK			(BIT(1) | BIT(2) | BIT(3))
28 #define BA431_STATUS_STATE_OFFSET		1
29 
30 enum ba431_state {
31 	BA431_STATE_RESET,
32 	BA431_STATE_STARTUP,
33 	BA431_STATE_FIFOFULLON,
34 	BA431_STATE_FIFOFULLOFF,
35 	BA431_STATE_RUNNING,
36 	BA431_STATE_ERROR
37 };
38 
39 struct ba431_trng {
40 	struct device *dev;
41 	void __iomem *base;
42 	struct hwrng rng;
43 	atomic_t reset_pending;
44 	struct work_struct reset_work;
45 };
46 
47 static inline u32 ba431_trng_read_reg(struct ba431_trng *ba431, u32 reg)
48 {
49 	return ioread32(ba431->base + reg);
50 }
51 
52 static inline void ba431_trng_write_reg(struct ba431_trng *ba431, u32 reg,
53 					u32 val)
54 {
55 	iowrite32(val, ba431->base + reg);
56 }
57 
58 static inline enum ba431_state ba431_trng_get_state(struct ba431_trng *ba431)
59 {
60 	u32 status = ba431_trng_read_reg(ba431, BA431_REG_STATUS);
61 
62 	return (status & BA431_STATUS_STATE_MASK) >> BA431_STATUS_STATE_OFFSET;
63 }
64 
65 static int ba431_trng_is_in_error(struct ba431_trng *ba431)
66 {
67 	enum ba431_state state = ba431_trng_get_state(ba431);
68 
69 	if ((state < BA431_STATE_STARTUP) ||
70 	    (state >= BA431_STATE_ERROR))
71 		return 1;
72 
73 	return 0;
74 }
75 
76 static int ba431_trng_reset(struct ba431_trng *ba431)
77 {
78 	int ret;
79 
80 	/* Disable interrupts, random generation and enable the softreset */
81 	ba431_trng_write_reg(ba431, BA431_REG_CTRL, BA431_CTRL_SOFTRESET);
82 	udelay(BA431_RESET_DELAY);
83 	ba431_trng_write_reg(ba431, BA431_REG_CTRL, BA431_CTRL_ENABLE);
84 
85 	/* Wait until the state changed */
86 	if (readx_poll_timeout(ba431_trng_is_in_error, ba431, ret, !ret,
87 			       BA431_RESET_READ_STATUS_INTERVAL,
88 			       BA431_RESET_READ_STATUS_TIMEOUT)) {
89 		dev_err(ba431->dev, "reset failed (state: %d)\n",
90 			ba431_trng_get_state(ba431));
91 		return -ETIMEDOUT;
92 	}
93 
94 	dev_info(ba431->dev, "reset done\n");
95 
96 	return 0;
97 }
98 
99 static void ba431_trng_reset_work(struct work_struct *work)
100 {
101 	struct ba431_trng *ba431 = container_of(work, struct ba431_trng,
102 						reset_work);
103 	ba431_trng_reset(ba431);
104 	atomic_set(&ba431->reset_pending, 0);
105 }
106 
107 static void ba431_trng_schedule_reset(struct ba431_trng *ba431)
108 {
109 	if (atomic_cmpxchg(&ba431->reset_pending, 0, 1))
110 		return;
111 
112 	schedule_work(&ba431->reset_work);
113 }
114 
115 static int ba431_trng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
116 {
117 	struct ba431_trng *ba431 = container_of(rng, struct ba431_trng, rng);
118 	u32 *data = buf;
119 	unsigned int level, i;
120 	int n = 0;
121 
122 	while (max > 0) {
123 		level = ba431_trng_read_reg(ba431, BA431_REG_FIFO_LEVEL);
124 		if (!level) {
125 			if (ba431_trng_is_in_error(ba431)) {
126 				ba431_trng_schedule_reset(ba431);
127 				break;
128 			}
129 
130 			if (!wait)
131 				break;
132 
133 			udelay(BA431_READ_RETRY_INTERVAL);
134 			continue;
135 		}
136 
137 		i = level;
138 		do {
139 			data[n++] = ba431_trng_read_reg(ba431,
140 							BA431_REG_FIFODATA);
141 			max -= sizeof(*data);
142 		} while (--i && (max > 0));
143 
144 		if (ba431_trng_is_in_error(ba431)) {
145 			n -= (level - i);
146 			ba431_trng_schedule_reset(ba431);
147 			break;
148 		}
149 	}
150 
151 	n *= sizeof(data);
152 	return (n || !wait) ? n : -EIO;
153 }
154 
155 static void ba431_trng_cleanup(struct hwrng *rng)
156 {
157 	struct ba431_trng *ba431 = container_of(rng, struct ba431_trng, rng);
158 
159 	ba431_trng_write_reg(ba431, BA431_REG_CTRL, 0);
160 	cancel_work_sync(&ba431->reset_work);
161 }
162 
163 static int ba431_trng_init(struct hwrng *rng)
164 {
165 	struct ba431_trng *ba431 = container_of(rng, struct ba431_trng, rng);
166 
167 	return ba431_trng_reset(ba431);
168 }
169 
170 static int ba431_trng_probe(struct platform_device *pdev)
171 {
172 	struct ba431_trng *ba431;
173 	int ret;
174 
175 	ba431 = devm_kzalloc(&pdev->dev, sizeof(*ba431), GFP_KERNEL);
176 	if (!ba431)
177 		return -ENOMEM;
178 
179 	ba431->dev = &pdev->dev;
180 
181 	ba431->base = devm_platform_ioremap_resource(pdev, 0);
182 	if (IS_ERR(ba431->base))
183 		return PTR_ERR(ba431->base);
184 
185 	atomic_set(&ba431->reset_pending, 0);
186 	INIT_WORK(&ba431->reset_work, ba431_trng_reset_work);
187 	ba431->rng.name = pdev->name;
188 	ba431->rng.init = ba431_trng_init;
189 	ba431->rng.cleanup = ba431_trng_cleanup;
190 	ba431->rng.read = ba431_trng_read;
191 
192 	platform_set_drvdata(pdev, ba431);
193 
194 	ret = devm_hwrng_register(&pdev->dev, &ba431->rng);
195 	if (ret) {
196 		dev_err(&pdev->dev, "BA431 registration failed (%d)\n", ret);
197 		return ret;
198 	}
199 
200 	dev_info(&pdev->dev, "BA431 TRNG registered\n");
201 
202 	return 0;
203 }
204 
205 static const struct of_device_id ba431_trng_dt_ids[] = {
206 	{ .compatible = "silex-insight,ba431-rng", .data = NULL },
207 	{ /* sentinel */ }
208 };
209 MODULE_DEVICE_TABLE(of, ba431_trng_dt_ids);
210 
211 static struct platform_driver ba431_trng_driver = {
212 	.driver = {
213 		.name = "ba431-rng",
214 		.of_match_table = ba431_trng_dt_ids,
215 	},
216 	.probe = ba431_trng_probe,
217 };
218 
219 module_platform_driver(ba431_trng_driver);
220 
221 MODULE_AUTHOR("Olivier Sobrie <olivier@sobrie.be>");
222 MODULE_DESCRIPTION("TRNG driver for Silex Insight BA431");
223 MODULE_LICENSE("GPL");
224