1// SPDX-License-Identifier: GPL-2.0
2/*
3 * exynos-rng.c - Random Number Generator driver for the Exynos
4 *
5 * Copyright (c) 2017 Krzysztof Kozlowski <krzk@kernel.org>
6 *
7 * Loosely based on old driver from drivers/char/hw_random/exynos-rng.c:
8 * Copyright (C) 2012 Samsung Electronics
9 * Jonghwa Lee <jonghwa3.lee@samsung.com>
10 */
11
12#include <linux/clk.h>
13#include <linux/crypto.h>
14#include <linux/err.h>
15#include <linux/io.h>
16#include <linux/module.h>
17#include <linux/mutex.h>
18#include <linux/of.h>
19#include <linux/platform_device.h>
20
21#include <crypto/internal/rng.h>
22
23#define EXYNOS_RNG_CONTROL		0x0
24#define EXYNOS_RNG_STATUS		0x10
25
26#define EXYNOS_RNG_SEED_CONF		0x14
27#define EXYNOS_RNG_GEN_PRNG	        BIT(1)
28
29#define EXYNOS_RNG_SEED_BASE		0x140
30#define EXYNOS_RNG_SEED(n)		(EXYNOS_RNG_SEED_BASE + (n * 0x4))
31#define EXYNOS_RNG_OUT_BASE		0x160
32#define EXYNOS_RNG_OUT(n)		(EXYNOS_RNG_OUT_BASE + (n * 0x4))
33
34/* EXYNOS_RNG_CONTROL bit fields */
35#define EXYNOS_RNG_CONTROL_START	0x18
36/* EXYNOS_RNG_STATUS bit fields */
37#define EXYNOS_RNG_STATUS_SEED_SETTING_DONE	BIT(1)
38#define EXYNOS_RNG_STATUS_RNG_DONE		BIT(5)
39
40/* Five seed and output registers, each 4 bytes */
41#define EXYNOS_RNG_SEED_REGS		5
42#define EXYNOS_RNG_SEED_SIZE		(EXYNOS_RNG_SEED_REGS * 4)
43
44enum exynos_prng_type {
45	EXYNOS_PRNG_UNKNOWN = 0,
46	EXYNOS_PRNG_EXYNOS4,
47	EXYNOS_PRNG_EXYNOS5,
48};
49
50/*
51 * Driver re-seeds itself with generated random numbers to hinder
52 * backtracking of the original seed.
53 *
54 * Time for next re-seed in ms.
55 */
56#define EXYNOS_RNG_RESEED_TIME		1000
57#define EXYNOS_RNG_RESEED_BYTES		65536
58
59/*
60 * In polling mode, do not wait infinitely for the engine to finish the work.
61 */
62#define EXYNOS_RNG_WAIT_RETRIES		100
63
64/* Context for crypto */
65struct exynos_rng_ctx {
66	struct exynos_rng_dev		*rng;
67};
68
69/* Device associated memory */
70struct exynos_rng_dev {
71	struct device			*dev;
72	enum exynos_prng_type		type;
73	void __iomem			*mem;
74	struct clk			*clk;
75	struct mutex 			lock;
76	/* Generated numbers stored for seeding during resume */
77	u8				seed_save[EXYNOS_RNG_SEED_SIZE];
78	unsigned int			seed_save_len;
79	/* Time of last seeding in jiffies */
80	unsigned long			last_seeding;
81	/* Bytes generated since last seeding */
82	unsigned long			bytes_seeding;
83};
84
85static struct exynos_rng_dev *exynos_rng_dev;
86
87static u32 exynos_rng_readl(struct exynos_rng_dev *rng, u32 offset)
88{
89	return readl_relaxed(rng->mem + offset);
90}
91
92static void exynos_rng_writel(struct exynos_rng_dev *rng, u32 val, u32 offset)
93{
94	writel_relaxed(val, rng->mem + offset);
95}
96
97static int exynos_rng_set_seed(struct exynos_rng_dev *rng,
98			       const u8 *seed, unsigned int slen)
99{
100	u32 val;
101	int i;
102
103	/* Round seed length because loop iterates over full register size */
104	slen = ALIGN_DOWN(slen, 4);
105
106	if (slen < EXYNOS_RNG_SEED_SIZE)
107		return -EINVAL;
108
109	for (i = 0; i < slen ; i += 4) {
110		unsigned int seed_reg = (i / 4) % EXYNOS_RNG_SEED_REGS;
111
112		val = seed[i] << 24;
113		val |= seed[i + 1] << 16;
114		val |= seed[i + 2] << 8;
115		val |= seed[i + 3] << 0;
116
117		exynos_rng_writel(rng, val, EXYNOS_RNG_SEED(seed_reg));
118	}
119
120	val = exynos_rng_readl(rng, EXYNOS_RNG_STATUS);
121	if (!(val & EXYNOS_RNG_STATUS_SEED_SETTING_DONE)) {
122		dev_warn(rng->dev, "Seed setting not finished\n");
123		return -EIO;
124	}
125
126	rng->last_seeding = jiffies;
127	rng->bytes_seeding = 0;
128
129	return 0;
130}
131
132/*
133 * Start the engine and poll for finish.  Then read from output registers
134 * filling the 'dst' buffer up to 'dlen' bytes or up to size of generated
135 * random data (EXYNOS_RNG_SEED_SIZE).
136 *
137 * On success: return 0 and store number of read bytes under 'read' address.
138 * On error: return -ERRNO.
139 */
140static int exynos_rng_get_random(struct exynos_rng_dev *rng,
141				 u8 *dst, unsigned int dlen,
142				 unsigned int *read)
143{
144	int retry = EXYNOS_RNG_WAIT_RETRIES;
145
146	if (rng->type == EXYNOS_PRNG_EXYNOS4) {
147		exynos_rng_writel(rng, EXYNOS_RNG_CONTROL_START,
148				  EXYNOS_RNG_CONTROL);
149	} else if (rng->type == EXYNOS_PRNG_EXYNOS5) {
150		exynos_rng_writel(rng, EXYNOS_RNG_GEN_PRNG,
151				  EXYNOS_RNG_SEED_CONF);
152	}
153
154	while (!(exynos_rng_readl(rng,
155			EXYNOS_RNG_STATUS) & EXYNOS_RNG_STATUS_RNG_DONE) && --retry)
156		cpu_relax();
157
158	if (!retry)
159		return -ETIMEDOUT;
160
161	/* Clear status bit */
162	exynos_rng_writel(rng, EXYNOS_RNG_STATUS_RNG_DONE,
163			  EXYNOS_RNG_STATUS);
164	*read = min_t(size_t, dlen, EXYNOS_RNG_SEED_SIZE);
165	memcpy_fromio(dst, rng->mem + EXYNOS_RNG_OUT_BASE, *read);
166	rng->bytes_seeding += *read;
167
168	return 0;
169}
170
171/* Re-seed itself from time to time */
172static void exynos_rng_reseed(struct exynos_rng_dev *rng)
173{
174	unsigned long next_seeding = rng->last_seeding + \
175				     msecs_to_jiffies(EXYNOS_RNG_RESEED_TIME);
176	unsigned long now = jiffies;
177	unsigned int read = 0;
178	u8 seed[EXYNOS_RNG_SEED_SIZE];
179
180	if (time_before(now, next_seeding) &&
181	    rng->bytes_seeding < EXYNOS_RNG_RESEED_BYTES)
182		return;
183
184	if (exynos_rng_get_random(rng, seed, sizeof(seed), &read))
185		return;
186
187	exynos_rng_set_seed(rng, seed, read);
188
189	/* Let others do some of their job. */
190	mutex_unlock(&rng->lock);
191	mutex_lock(&rng->lock);
192}
193
194static int exynos_rng_generate(struct crypto_rng *tfm,
195			       const u8 *src, unsigned int slen,
196			       u8 *dst, unsigned int dlen)
197{
198	struct exynos_rng_ctx *ctx = crypto_rng_ctx(tfm);
199	struct exynos_rng_dev *rng = ctx->rng;
200	unsigned int read = 0;
201	int ret;
202
203	ret = clk_prepare_enable(rng->clk);
204	if (ret)
205		return ret;
206
207	mutex_lock(&rng->lock);
208	do {
209		ret = exynos_rng_get_random(rng, dst, dlen, &read);
210		if (ret)
211			break;
212
213		dlen -= read;
214		dst += read;
215
216		exynos_rng_reseed(rng);
217	} while (dlen > 0);
218	mutex_unlock(&rng->lock);
219
220	clk_disable_unprepare(rng->clk);
221
222	return ret;
223}
224
225static int exynos_rng_seed(struct crypto_rng *tfm, const u8 *seed,
226			   unsigned int slen)
227{
228	struct exynos_rng_ctx *ctx = crypto_rng_ctx(tfm);
229	struct exynos_rng_dev *rng = ctx->rng;
230	int ret;
231
232	ret = clk_prepare_enable(rng->clk);
233	if (ret)
234		return ret;
235
236	mutex_lock(&rng->lock);
237	ret = exynos_rng_set_seed(ctx->rng, seed, slen);
238	mutex_unlock(&rng->lock);
239
240	clk_disable_unprepare(rng->clk);
241
242	return ret;
243}
244
245static int exynos_rng_kcapi_init(struct crypto_tfm *tfm)
246{
247	struct exynos_rng_ctx *ctx = crypto_tfm_ctx(tfm);
248
249	ctx->rng = exynos_rng_dev;
250
251	return 0;
252}
253
254static struct rng_alg exynos_rng_alg = {
255	.generate		= exynos_rng_generate,
256	.seed			= exynos_rng_seed,
257	.seedsize		= EXYNOS_RNG_SEED_SIZE,
258	.base			= {
259		.cra_name		= "stdrng",
260		.cra_driver_name	= "exynos_rng",
261		.cra_priority		= 300,
262		.cra_ctxsize		= sizeof(struct exynos_rng_ctx),
263		.cra_module		= THIS_MODULE,
264		.cra_init		= exynos_rng_kcapi_init,
265	}
266};
267
268static int exynos_rng_probe(struct platform_device *pdev)
269{
270	struct exynos_rng_dev *rng;
271	int ret;
272
273	if (exynos_rng_dev)
274		return -EEXIST;
275
276	rng = devm_kzalloc(&pdev->dev, sizeof(*rng), GFP_KERNEL);
277	if (!rng)
278		return -ENOMEM;
279
280	rng->type = (uintptr_t)of_device_get_match_data(&pdev->dev);
281
282	mutex_init(&rng->lock);
283
284	rng->dev = &pdev->dev;
285	rng->clk = devm_clk_get(&pdev->dev, "secss");
286	if (IS_ERR(rng->clk)) {
287		dev_err(&pdev->dev, "Couldn't get clock.\n");
288		return PTR_ERR(rng->clk);
289	}
290
291	rng->mem = devm_platform_ioremap_resource(pdev, 0);
292	if (IS_ERR(rng->mem))
293		return PTR_ERR(rng->mem);
294
295	platform_set_drvdata(pdev, rng);
296
297	exynos_rng_dev = rng;
298
299	ret = crypto_register_rng(&exynos_rng_alg);
300	if (ret) {
301		dev_err(&pdev->dev,
302			"Couldn't register rng crypto alg: %d\n", ret);
303		exynos_rng_dev = NULL;
304	}
305
306	return ret;
307}
308
309static void exynos_rng_remove(struct platform_device *pdev)
310{
311	crypto_unregister_rng(&exynos_rng_alg);
312
313	exynos_rng_dev = NULL;
314}
315
316static int __maybe_unused exynos_rng_suspend(struct device *dev)
317{
318	struct exynos_rng_dev *rng = dev_get_drvdata(dev);
319	int ret;
320
321	/* If we were never seeded then after resume it will be the same */
322	if (!rng->last_seeding)
323		return 0;
324
325	rng->seed_save_len = 0;
326	ret = clk_prepare_enable(rng->clk);
327	if (ret)
328		return ret;
329
330	mutex_lock(&rng->lock);
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
336	mutex_unlock(&rng->lock);
337
338	dev_dbg(rng->dev, "Stored %u bytes for seeding on system resume\n",
339		rng->seed_save_len);
340
341	clk_disable_unprepare(rng->clk);
342
343	return 0;
344}
345
346static int __maybe_unused exynos_rng_resume(struct device *dev)
347{
348	struct exynos_rng_dev *rng = dev_get_drvdata(dev);
349	int ret;
350
351	/* Never seeded so nothing to do */
352	if (!rng->last_seeding)
353		return 0;
354
355	ret = clk_prepare_enable(rng->clk);
356	if (ret)
357		return ret;
358
359	mutex_lock(&rng->lock);
360
361	ret = exynos_rng_set_seed(rng, rng->seed_save, rng->seed_save_len);
362
363	mutex_unlock(&rng->lock);
364
365	clk_disable_unprepare(rng->clk);
366
367	return ret;
368}
369
370static SIMPLE_DEV_PM_OPS(exynos_rng_pm_ops, exynos_rng_suspend,
371			 exynos_rng_resume);
372
373static const struct of_device_id exynos_rng_dt_match[] = {
374	{
375		.compatible = "samsung,exynos4-rng",
376		.data = (const void *)EXYNOS_PRNG_EXYNOS4,
377	}, {
378		.compatible = "samsung,exynos5250-prng",
379		.data = (const void *)EXYNOS_PRNG_EXYNOS5,
380	},
381	{ },
382};
383MODULE_DEVICE_TABLE(of, exynos_rng_dt_match);
384
385static struct platform_driver exynos_rng_driver = {
386	.driver		= {
387		.name	= "exynos-rng",
388		.pm	= &exynos_rng_pm_ops,
389		.of_match_table = exynos_rng_dt_match,
390	},
391	.probe		= exynos_rng_probe,
392	.remove_new	= exynos_rng_remove,
393};
394
395module_platform_driver(exynos_rng_driver);
396
397MODULE_DESCRIPTION("Exynos H/W Random Number Generator driver");
398MODULE_AUTHOR("Krzysztof Kozlowski <krzk@kernel.org>");
399MODULE_LICENSE("GPL v2");
400