xref: /openbmc/linux/drivers/crypto/exynos-rng.c (revision 68198dca) 
1 /*
2  * exynos-rng.c - Random Number Generator driver for the Exynos
3  *
4  * Copyright (c) 2017 Krzysztof Kozlowski <krzk@kernel.org>
5  *
6  * Loosely based on old driver from drivers/char/hw_random/exynos-rng.c:
7  * Copyright (C) 2012 Samsung Electronics
8  * Jonghwa Lee <jonghwa3.lee@samsung.com>
9  *
10  * This program is free software; you can redistribute it and/or modify
11  * it under the terms of the GNU General Public License as published by
12  * the Free Software Foundation;
13  *
14  * This program is distributed in the hope that it will be useful,
15  * but WITHOUT ANY WARRANTY; without even the implied warranty of
16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
17  * GNU General Public License for more details.
18  */
19 
20 #include <linux/clk.h>
21 #include <linux/crypto.h>
22 #include <linux/err.h>
23 #include <linux/io.h>
24 #include <linux/module.h>
25 #include <linux/platform_device.h>
26 
27 #include <crypto/internal/rng.h>
28 
29 #define EXYNOS_RNG_CONTROL		0x0
30 #define EXYNOS_RNG_STATUS		0x10
31 #define EXYNOS_RNG_SEED_BASE		0x140
32 #define EXYNOS_RNG_SEED(n)		(EXYNOS_RNG_SEED_BASE + (n * 0x4))
33 #define EXYNOS_RNG_OUT_BASE		0x160
34 #define EXYNOS_RNG_OUT(n)		(EXYNOS_RNG_OUT_BASE + (n * 0x4))
35 
36 /* EXYNOS_RNG_CONTROL bit fields */
37 #define EXYNOS_RNG_CONTROL_START	0x18
38 /* EXYNOS_RNG_STATUS bit fields */
39 #define EXYNOS_RNG_STATUS_SEED_SETTING_DONE	BIT(1)
40 #define EXYNOS_RNG_STATUS_RNG_DONE		BIT(5)
41 
42 /* Five seed and output registers, each 4 bytes */
43 #define EXYNOS_RNG_SEED_REGS		5
44 #define EXYNOS_RNG_SEED_SIZE		(EXYNOS_RNG_SEED_REGS * 4)
45 
46 /*
47  * Driver re-seeds itself with generated random numbers to increase
48  * the randomness.
49  *
50  * Time for next re-seed in ms.
51  */
52 #define EXYNOS_RNG_RESEED_TIME		100
53 /*
54  * In polling mode, do not wait infinitely for the engine to finish the work.
55  */
56 #define EXYNOS_RNG_WAIT_RETRIES		100
57 
58 /* Context for crypto */
59 struct exynos_rng_ctx {
60 	struct exynos_rng_dev		*rng;
61 };
62 
63 /* Device associated memory */
64 struct exynos_rng_dev {
65 	struct device			*dev;
66 	void __iomem			*mem;
67 	struct clk			*clk;
68 	/* Generated numbers stored for seeding during resume */
69 	u8				seed_save[EXYNOS_RNG_SEED_SIZE];
70 	unsigned int			seed_save_len;
71 	/* Time of last seeding in jiffies */
72 	unsigned long			last_seeding;
73 };
74 
75 static struct exynos_rng_dev *exynos_rng_dev;
76 
77 static u32 exynos_rng_readl(struct exynos_rng_dev *rng, u32 offset)
78 {
79 	return readl_relaxed(rng->mem + offset);
80 }
81 
82 static void exynos_rng_writel(struct exynos_rng_dev *rng, u32 val, u32 offset)
83 {
84 	writel_relaxed(val, rng->mem + offset);
85 }
86 
87 static int exynos_rng_set_seed(struct exynos_rng_dev *rng,
88 			       const u8 *seed, unsigned int slen)
89 {
90 	u32 val;
91 	int i;
92 
93 	/* Round seed length because loop iterates over full register size */
94 	slen = ALIGN_DOWN(slen, 4);
95 
96 	if (slen < EXYNOS_RNG_SEED_SIZE)
97 		return -EINVAL;
98 
99 	for (i = 0; i < slen ; i += 4) {
100 		unsigned int seed_reg = (i / 4) % EXYNOS_RNG_SEED_REGS;
101 
102 		val = seed[i] << 24;
103 		val |= seed[i + 1] << 16;
104 		val |= seed[i + 2] << 8;
105 		val |= seed[i + 3] << 0;
106 
107 		exynos_rng_writel(rng, val, EXYNOS_RNG_SEED(seed_reg));
108 	}
109 
110 	val = exynos_rng_readl(rng, EXYNOS_RNG_STATUS);
111 	if (!(val & EXYNOS_RNG_STATUS_SEED_SETTING_DONE)) {
112 		dev_warn(rng->dev, "Seed setting not finished\n");
113 		return -EIO;
114 	}
115 
116 	rng->last_seeding = jiffies;
117 
118 	return 0;
119 }
120 
121 /*
122  * Read from output registers and put the data under 'dst' array,
123  * up to dlen bytes.
124  *
125  * Returns number of bytes actually stored in 'dst' (dlen
126  * or EXYNOS_RNG_SEED_SIZE).
127  */
128 static unsigned int exynos_rng_copy_random(struct exynos_rng_dev *rng,
129 					   u8 *dst, unsigned int dlen)
130 {
131 	unsigned int cnt = 0;
132 	int i, j;
133 	u32 val;
134 
135 	for (j = 0; j < EXYNOS_RNG_SEED_REGS; j++) {
136 		val = exynos_rng_readl(rng, EXYNOS_RNG_OUT(j));
137 
138 		for (i = 0; i < 4; i++) {
139 			dst[cnt] = val & 0xff;
140 			val >>= 8;
141 			if (++cnt >= dlen)
142 				return cnt;
143 		}
144 	}
145 
146 	return cnt;
147 }
148 
149 /*
150  * Start the engine and poll for finish.  Then read from output registers
151  * filling the 'dst' buffer up to 'dlen' bytes or up to size of generated
152  * random data (EXYNOS_RNG_SEED_SIZE).
153  *
154  * On success: return 0 and store number of read bytes under 'read' address.
155  * On error: return -ERRNO.
156  */
157 static int exynos_rng_get_random(struct exynos_rng_dev *rng,
158 				 u8 *dst, unsigned int dlen,
159 				 unsigned int *read)
160 {
161 	int retry = EXYNOS_RNG_WAIT_RETRIES;
162 
163 	exynos_rng_writel(rng, EXYNOS_RNG_CONTROL_START,
164 			  EXYNOS_RNG_CONTROL);
165 
166 	while (!(exynos_rng_readl(rng,
167 			EXYNOS_RNG_STATUS) & EXYNOS_RNG_STATUS_RNG_DONE) && --retry)
168 		cpu_relax();
169 
170 	if (!retry)
171 		return -ETIMEDOUT;
172 
173 	/* Clear status bit */
174 	exynos_rng_writel(rng, EXYNOS_RNG_STATUS_RNG_DONE,
175 			  EXYNOS_RNG_STATUS);
176 	*read = exynos_rng_copy_random(rng, dst, dlen);
177 
178 	return 0;
179 }
180 
181 /* Re-seed itself from time to time */
182 static void exynos_rng_reseed(struct exynos_rng_dev *rng)
183 {
184 	unsigned long next_seeding = rng->last_seeding + \
185 				     msecs_to_jiffies(EXYNOS_RNG_RESEED_TIME);
186 	unsigned long now = jiffies;
187 	unsigned int read = 0;
188 	u8 seed[EXYNOS_RNG_SEED_SIZE];
189 
190 	if (time_before(now, next_seeding))
191 		return;
192 
193 	if (exynos_rng_get_random(rng, seed, sizeof(seed), &read))
194 		return;
195 
196 	exynos_rng_set_seed(rng, seed, read);
197 }
198 
199 static int exynos_rng_generate(struct crypto_rng *tfm,
200 			       const u8 *src, unsigned int slen,
201 			       u8 *dst, unsigned int dlen)
202 {
203 	struct exynos_rng_ctx *ctx = crypto_rng_ctx(tfm);
204 	struct exynos_rng_dev *rng = ctx->rng;
205 	unsigned int read = 0;
206 	int ret;
207 
208 	ret = clk_prepare_enable(rng->clk);
209 	if (ret)
210 		return ret;
211 
212 	do {
213 		ret = exynos_rng_get_random(rng, dst, dlen, &read);
214 		if (ret)
215 			break;
216 
217 		dlen -= read;
218 		dst += read;
219 
220 		exynos_rng_reseed(rng);
221 	} while (dlen > 0);
222 
223 	clk_disable_unprepare(rng->clk);
224 
225 	return ret;
226 }
227 
228 static int exynos_rng_seed(struct crypto_rng *tfm, const u8 *seed,
229 			   unsigned int slen)
230 {
231 	struct exynos_rng_ctx *ctx = crypto_rng_ctx(tfm);
232 	struct exynos_rng_dev *rng = ctx->rng;
233 	int ret;
234 
235 	ret = clk_prepare_enable(rng->clk);
236 	if (ret)
237 		return ret;
238 
239 	ret = exynos_rng_set_seed(ctx->rng, seed, slen);
240 
241 	clk_disable_unprepare(rng->clk);
242 
243 	return ret;
244 }
245 
246 static int exynos_rng_kcapi_init(struct crypto_tfm *tfm)
247 {
248 	struct exynos_rng_ctx *ctx = crypto_tfm_ctx(tfm);
249 
250 	ctx->rng = exynos_rng_dev;
251 
252 	return 0;
253 }
254 
255 static struct rng_alg exynos_rng_alg = {
256 	.generate		= exynos_rng_generate,
257 	.seed			= exynos_rng_seed,
258 	.seedsize		= EXYNOS_RNG_SEED_SIZE,
259 	.base			= {
260 		.cra_name		= "stdrng",
261 		.cra_driver_name	= "exynos_rng",
262 		.cra_priority		= 100,
263 		.cra_ctxsize		= sizeof(struct exynos_rng_ctx),
264 		.cra_module		= THIS_MODULE,
265 		.cra_init		= exynos_rng_kcapi_init,
266 	}
267 };
268 
269 static int exynos_rng_probe(struct platform_device *pdev)
270 {
271 	struct exynos_rng_dev *rng;
272 	struct resource *res;
273 	int ret;
274 
275 	if (exynos_rng_dev)
276 		return -EEXIST;
277 
278 	rng = devm_kzalloc(&pdev->dev, sizeof(*rng), GFP_KERNEL);
279 	if (!rng)
280 		return -ENOMEM;
281 
282 	rng->dev = &pdev->dev;
283 	rng->clk = devm_clk_get(&pdev->dev, "secss");
284 	if (IS_ERR(rng->clk)) {
285 		dev_err(&pdev->dev, "Couldn't get clock.\n");
286 		return PTR_ERR(rng->clk);
287 	}
288 
289 	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
290 	rng->mem = devm_ioremap_resource(&pdev->dev, res);
291 	if (IS_ERR(rng->mem))
292 		return PTR_ERR(rng->mem);
293 
294 	platform_set_drvdata(pdev, rng);
295 
296 	exynos_rng_dev = rng;
297 
298 	ret = crypto_register_rng(&exynos_rng_alg);
299 	if (ret) {
300 		dev_err(&pdev->dev,
301 			"Couldn't register rng crypto alg: %d\n", ret);
302 		exynos_rng_dev = NULL;
303 	}
304 
305 	return ret;
306 }
307 
308 static int exynos_rng_remove(struct platform_device *pdev)
309 {
310 	crypto_unregister_rng(&exynos_rng_alg);
311 
312 	exynos_rng_dev = NULL;
313 
314 	return 0;
315 }
316 
317 static int __maybe_unused exynos_rng_suspend(struct device *dev)
318 {
319 	struct platform_device *pdev = to_platform_device(dev);
320 	struct exynos_rng_dev *rng = platform_get_drvdata(pdev);
321 	int ret;
322 
323 	/* If we were never seeded then after resume it will be the same */
324 	if (!rng->last_seeding)
325 		return 0;
326 
327 	rng->seed_save_len = 0;
328 	ret = clk_prepare_enable(rng->clk);
329 	if (ret)
330 		return ret;
331 
332 	/* Get new random numbers and store them for seeding on resume. */
333 	exynos_rng_get_random(rng, rng->seed_save, sizeof(rng->seed_save),
334 			      &(rng->seed_save_len));
335 	dev_dbg(rng->dev, "Stored %u bytes for seeding on system resume\n",
336 		rng->seed_save_len);
337 
338 	clk_disable_unprepare(rng->clk);
339 
340 	return 0;
341 }
342 
343 static int __maybe_unused exynos_rng_resume(struct device *dev)
344 {
345 	struct platform_device *pdev = to_platform_device(dev);
346 	struct exynos_rng_dev *rng = platform_get_drvdata(pdev);
347 	int ret;
348 
349 	/* Never seeded so nothing to do */
350 	if (!rng->last_seeding)
351 		return 0;
352 
353 	ret = clk_prepare_enable(rng->clk);
354 	if (ret)
355 		return ret;
356 
357 	ret = exynos_rng_set_seed(rng, rng->seed_save, rng->seed_save_len);
358 
359 	clk_disable_unprepare(rng->clk);
360 
361 	return ret;
362 }
363 
364 static SIMPLE_DEV_PM_OPS(exynos_rng_pm_ops, exynos_rng_suspend,
365 			 exynos_rng_resume);
366 
367 static const struct of_device_id exynos_rng_dt_match[] = {
368 	{
369 		.compatible = "samsung,exynos4-rng",
370 	},
371 	{ },
372 };
373 MODULE_DEVICE_TABLE(of, exynos_rng_dt_match);
374 
375 static struct platform_driver exynos_rng_driver = {
376 	.driver		= {
377 		.name	= "exynos-rng",
378 		.pm	= &exynos_rng_pm_ops,
379 		.of_match_table = exynos_rng_dt_match,
380 	},
381 	.probe		= exynos_rng_probe,
382 	.remove		= exynos_rng_remove,
383 };
384 
385 module_platform_driver(exynos_rng_driver);
386 
387 MODULE_DESCRIPTION("Exynos H/W Random Number Generator driver");
388 MODULE_AUTHOR("Krzysztof Kozlowski <krzk@kernel.org>");
389 MODULE_LICENSE("GPL");
390