drivers/crypto/exynos-rng.c - kernel/msm-5.4 - Gitiles

 // SPDX-License-Identifier: GPL-2.0
 /*
  * exynos-rng.c - Random Number Generator driver for the Exynos
  *
  * Copyright (c) 2017 Krzysztof Kozlowski <krzk@kernel.org>
  *
  * Loosely based on old driver from drivers/char/hw_random/exynos-rng.c:
  * Copyright (C) 2012 Samsung Electronics
  * Jonghwa Lee <jonghwa3.lee@samsung.com>
  */

 #include <linux/clk.h>
 #include <linux/crypto.h>
 #include <linux/err.h>
 #include <linux/io.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
 #include <linux/of_device.h>
 #include <linux/platform_device.h>

 #include <crypto/internal/rng.h>

 #define EXYNOS_RNG_CONTROL		0x0
 #define EXYNOS_RNG_STATUS		0x10

 #define EXYNOS_RNG_SEED_CONF		0x14
 #define EXYNOS_RNG_GEN_PRNG	        BIT(1)

 #define EXYNOS_RNG_SEED_BASE		0x140
 #define EXYNOS_RNG_SEED(n)		(EXYNOS_RNG_SEED_BASE + (n * 0x4))
 #define EXYNOS_RNG_OUT_BASE		0x160
 #define EXYNOS_RNG_OUT(n)		(EXYNOS_RNG_OUT_BASE + (n * 0x4))

 /* EXYNOS_RNG_CONTROL bit fields */
 #define EXYNOS_RNG_CONTROL_START	0x18
 /* EXYNOS_RNG_STATUS bit fields */
 #define EXYNOS_RNG_STATUS_SEED_SETTING_DONE	BIT(1)
 #define EXYNOS_RNG_STATUS_RNG_DONE		BIT(5)

 /* Five seed and output registers, each 4 bytes */
 #define EXYNOS_RNG_SEED_REGS		5
 #define EXYNOS_RNG_SEED_SIZE		(EXYNOS_RNG_SEED_REGS * 4)

 enum exynos_prng_type {
 	EXYNOS_PRNG_UNKNOWN = 0,
 	EXYNOS_PRNG_EXYNOS4,
 	EXYNOS_PRNG_EXYNOS5,
 };

 /*
  * Driver re-seeds itself with generated random numbers to hinder
  * backtracking of the original seed.
  *
  * Time for next re-seed in ms.
  */
 #define EXYNOS_RNG_RESEED_TIME		1000
 #define EXYNOS_RNG_RESEED_BYTES		65536

 /*
  * In polling mode, do not wait infinitely for the engine to finish the work.
  */
 #define EXYNOS_RNG_WAIT_RETRIES		100

 /* Context for crypto */
 struct exynos_rng_ctx {
 	struct exynos_rng_dev		*rng;
 };

 /* Device associated memory */
 struct exynos_rng_dev {
 	struct device			*dev;
 	enum exynos_prng_type		type;
 	void __iomem			*mem;
 	struct clk			*clk;
 	struct mutex 			lock;
 	/* Generated numbers stored for seeding during resume */
 	u8				seed_save[EXYNOS_RNG_SEED_SIZE];
 	unsigned int			seed_save_len;
 	/* Time of last seeding in jiffies */
 	unsigned long			last_seeding;
 	/* Bytes generated since last seeding */
 	unsigned long			bytes_seeding;
 };

 static struct exynos_rng_dev *exynos_rng_dev;

 static u32 exynos_rng_readl(struct exynos_rng_dev *rng, u32 offset)
 {
 	return readl_relaxed(rng->mem + offset);
 }

 static void exynos_rng_writel(struct exynos_rng_dev *rng, u32 val, u32 offset)
 {
 	writel_relaxed(val, rng->mem + offset);
 }

 static int exynos_rng_set_seed(struct exynos_rng_dev *rng,
 			       const u8 *seed, unsigned int slen)
 {
 	u32 val;
 	int i;

 	/* Round seed length because loop iterates over full register size */
 	slen = ALIGN_DOWN(slen, 4);

 	if (slen < EXYNOS_RNG_SEED_SIZE)
 		return -EINVAL;

 	for (i = 0; i < slen ; i += 4) {
 		unsigned int seed_reg = (i / 4) % EXYNOS_RNG_SEED_REGS;

 		val = seed[i] << 24;
 		val |= seed[i + 1] << 16;
 		val |= seed[i + 2] << 8;
 		val |= seed[i + 3] << 0;

 		exynos_rng_writel(rng, val, EXYNOS_RNG_SEED(seed_reg));
 	}

 	val = exynos_rng_readl(rng, EXYNOS_RNG_STATUS);
 	if (!(val & EXYNOS_RNG_STATUS_SEED_SETTING_DONE)) {
 		dev_warn(rng->dev, "Seed setting not finished\n");
 		return -EIO;
 	}

 	rng->last_seeding = jiffies;
 	rng->bytes_seeding = 0;

 	return 0;
 }

 /*
  * Start the engine and poll for finish.  Then read from output registers
  * filling the 'dst' buffer up to 'dlen' bytes or up to size of generated
  * random data (EXYNOS_RNG_SEED_SIZE).
  *
  * On success: return 0 and store number of read bytes under 'read' address.
  * On error: return -ERRNO.
  */
 static int exynos_rng_get_random(struct exynos_rng_dev *rng,
 				 u8 *dst, unsigned int dlen,
 				 unsigned int *read)
 {
 	int retry = EXYNOS_RNG_WAIT_RETRIES;

 	if (rng->type == EXYNOS_PRNG_EXYNOS4) {
 		exynos_rng_writel(rng, EXYNOS_RNG_CONTROL_START,
 				  EXYNOS_RNG_CONTROL);
 	} else if (rng->type == EXYNOS_PRNG_EXYNOS5) {
 		exynos_rng_writel(rng, EXYNOS_RNG_GEN_PRNG,
 				  EXYNOS_RNG_SEED_CONF);
 	}

 	while (!(exynos_rng_readl(rng,
 			EXYNOS_RNG_STATUS) & EXYNOS_RNG_STATUS_RNG_DONE) && --retry)
 		cpu_relax();

 	if (!retry)
 		return -ETIMEDOUT;

 	/* Clear status bit */
 	exynos_rng_writel(rng, EXYNOS_RNG_STATUS_RNG_DONE,
 			  EXYNOS_RNG_STATUS);
 	*read = min_t(size_t, dlen, EXYNOS_RNG_SEED_SIZE);
 	memcpy_fromio(dst, rng->mem + EXYNOS_RNG_OUT_BASE, *read);
 	rng->bytes_seeding += *read;

 	return 0;
 }

 /* Re-seed itself from time to time */
 static void exynos_rng_reseed(struct exynos_rng_dev *rng)
 {
 	unsigned long next_seeding = rng->last_seeding + \
 				     msecs_to_jiffies(EXYNOS_RNG_RESEED_TIME);
 	unsigned long now = jiffies;
 	unsigned int read = 0;
 	u8 seed[EXYNOS_RNG_SEED_SIZE];

 	if (time_before(now, next_seeding) &&
 	    rng->bytes_seeding < EXYNOS_RNG_RESEED_BYTES)
 		return;

 	if (exynos_rng_get_random(rng, seed, sizeof(seed), &read))
 		return;

 	exynos_rng_set_seed(rng, seed, read);

 	/* Let others do some of their job. */
 	mutex_unlock(&rng->lock);
 	mutex_lock(&rng->lock);
 }

 static int exynos_rng_generate(struct crypto_rng *tfm,
 			       const u8 *src, unsigned int slen,
 			       u8 *dst, unsigned int dlen)
 {
 	struct exynos_rng_ctx *ctx = crypto_rng_ctx(tfm);
 	struct exynos_rng_dev *rng = ctx->rng;
 	unsigned int read = 0;
 	int ret;

 	ret = clk_prepare_enable(rng->clk);
 	if (ret)
 		return ret;

 	mutex_lock(&rng->lock);
 	do {
 		ret = exynos_rng_get_random(rng, dst, dlen, &read);
 		if (ret)
 			break;

 		dlen -= read;
 		dst += read;

 		exynos_rng_reseed(rng);
 	} while (dlen > 0);
 	mutex_unlock(&rng->lock);

 	clk_disable_unprepare(rng->clk);

 	return ret;
 }

 static int exynos_rng_seed(struct crypto_rng *tfm, const u8 *seed,
 			   unsigned int slen)
 {
 	struct exynos_rng_ctx *ctx = crypto_rng_ctx(tfm);
 	struct exynos_rng_dev *rng = ctx->rng;
 	int ret;

 	ret = clk_prepare_enable(rng->clk);
 	if (ret)
 		return ret;

 	mutex_lock(&rng->lock);
 	ret = exynos_rng_set_seed(ctx->rng, seed, slen);
 	mutex_unlock(&rng->lock);

 	clk_disable_unprepare(rng->clk);

 	return ret;
 }

 static int exynos_rng_kcapi_init(struct crypto_tfm *tfm)
 {
 	struct exynos_rng_ctx *ctx = crypto_tfm_ctx(tfm);

 	ctx->rng = exynos_rng_dev;

 	return 0;
 }

 static struct rng_alg exynos_rng_alg = {
 	.generate		= exynos_rng_generate,
 	.seed			= exynos_rng_seed,
 	.seedsize		= EXYNOS_RNG_SEED_SIZE,
 	.base			= {
 		.cra_name		= "stdrng",
 		.cra_driver_name	= "exynos_rng",
 		.cra_priority		= 300,
 		.cra_ctxsize		= sizeof(struct exynos_rng_ctx),
 		.cra_module		= THIS_MODULE,
 		.cra_init		= exynos_rng_kcapi_init,
 	}
 };

 static int exynos_rng_probe(struct platform_device *pdev)
 {
 	struct exynos_rng_dev *rng;
 	struct resource *res;
 	int ret;

 	if (exynos_rng_dev)
 		return -EEXIST;

 	rng = devm_kzalloc(&pdev->dev, sizeof(*rng), GFP_KERNEL);
 	if (!rng)
 		return -ENOMEM;

 	rng->type = (enum exynos_prng_type)of_device_get_match_data(&pdev->dev);

 	mutex_init(&rng->lock);

 	rng->dev = &pdev->dev;
 	rng->clk = devm_clk_get(&pdev->dev, "secss");
 	if (IS_ERR(rng->clk)) {
 		dev_err(&pdev->dev, "Couldn't get clock.\n");
 		return PTR_ERR(rng->clk);
 	}

 	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
 	rng->mem = devm_ioremap_resource(&pdev->dev, res);
 	if (IS_ERR(rng->mem))
 		return PTR_ERR(rng->mem);

 	platform_set_drvdata(pdev, rng);

 	exynos_rng_dev = rng;

 	ret = crypto_register_rng(&exynos_rng_alg);
 	if (ret) {
 		dev_err(&pdev->dev,
 			"Couldn't register rng crypto alg: %d\n", ret);
 		exynos_rng_dev = NULL;
 	}

 	return ret;
 }

 static int exynos_rng_remove(struct platform_device *pdev)
 {
 	crypto_unregister_rng(&exynos_rng_alg);

 	exynos_rng_dev = NULL;

 	return 0;
 }

 static int __maybe_unused exynos_rng_suspend(struct device *dev)
 {
 	struct platform_device *pdev = to_platform_device(dev);
 	struct exynos_rng_dev *rng = platform_get_drvdata(pdev);
 	int ret;

 	/* If we were never seeded then after resume it will be the same */
 	if (!rng->last_seeding)
 		return 0;

 	rng->seed_save_len = 0;
 	ret = clk_prepare_enable(rng->clk);
 	if (ret)
 		return ret;

 	mutex_lock(&rng->lock);

 	/* Get new random numbers and store them for seeding on resume. */
 	exynos_rng_get_random(rng, rng->seed_save, sizeof(rng->seed_save),
 			      &(rng->seed_save_len));

 	mutex_unlock(&rng->lock);

 	dev_dbg(rng->dev, "Stored %u bytes for seeding on system resume\n",
 		rng->seed_save_len);

 	clk_disable_unprepare(rng->clk);

 	return 0;
 }

 static int __maybe_unused exynos_rng_resume(struct device *dev)
 {
 	struct platform_device *pdev = to_platform_device(dev);
 	struct exynos_rng_dev *rng = platform_get_drvdata(pdev);
 	int ret;

 	/* Never seeded so nothing to do */
 	if (!rng->last_seeding)
 		return 0;

 	ret = clk_prepare_enable(rng->clk);
 	if (ret)
 		return ret;

 	mutex_lock(&rng->lock);

 	ret = exynos_rng_set_seed(rng, rng->seed_save, rng->seed_save_len);

 	mutex_unlock(&rng->lock);

 	clk_disable_unprepare(rng->clk);

 	return ret;
 }

 static SIMPLE_DEV_PM_OPS(exynos_rng_pm_ops, exynos_rng_suspend,
 			 exynos_rng_resume);

 static const struct of_device_id exynos_rng_dt_match[] = {
 	{
 		.compatible = "samsung,exynos4-rng",
 		.data = (const void *)EXYNOS_PRNG_EXYNOS4,
 	}, {
 		.compatible = "samsung,exynos5250-prng",
 		.data = (const void *)EXYNOS_PRNG_EXYNOS5,
 	},
 	{ },
 };
 MODULE_DEVICE_TABLE(of, exynos_rng_dt_match);

 static struct platform_driver exynos_rng_driver = {
 	.driver		= {
 		.name	= "exynos-rng",
 		.pm	= &exynos_rng_pm_ops,
 		.of_match_table = exynos_rng_dt_match,
 	},
 	.probe		= exynos_rng_probe,
 	.remove		= exynos_rng_remove,
 };

 module_platform_driver(exynos_rng_driver);

 MODULE_DESCRIPTION("Exynos H/W Random Number Generator driver");
 MODULE_AUTHOR("Krzysztof Kozlowski <krzk@kernel.org>");
 MODULE_LICENSE("GPL v2");
	// SPDX-License-Identifier: GPL-2.0
	/*
	* exynos-rng.c - Random Number Generator driver for the Exynos
	*
	* Copyright (c) 2017 Krzysztof Kozlowski <krzk@kernel.org>
	*
	* Loosely based on old driver from drivers/char/hw_random/exynos-rng.c:
	* Copyright (C) 2012 Samsung Electronics
	* Jonghwa Lee <jonghwa3.lee@samsung.com>
	*/

	#include <linux/clk.h>
	#include <linux/crypto.h>
	#include <linux/err.h>
	#include <linux/io.h>
	#include <linux/module.h>
	#include <linux/mutex.h>
	#include <linux/of_device.h>
	#include <linux/platform_device.h>

	#include <crypto/internal/rng.h>

	#define EXYNOS_RNG_CONTROL 0x0
	#define EXYNOS_RNG_STATUS 0x10

	#define EXYNOS_RNG_SEED_CONF 0x14
	#define EXYNOS_RNG_GEN_PRNG BIT(1)

	#define EXYNOS_RNG_SEED_BASE 0x140
	#define EXYNOS_RNG_SEED(n) (EXYNOS_RNG_SEED_BASE + (n * 0x4))
	#define EXYNOS_RNG_OUT_BASE 0x160
	#define EXYNOS_RNG_OUT(n) (EXYNOS_RNG_OUT_BASE + (n * 0x4))

	/* EXYNOS_RNG_CONTROL bit fields */
	#define EXYNOS_RNG_CONTROL_START 0x18
	/* EXYNOS_RNG_STATUS bit fields */
	#define EXYNOS_RNG_STATUS_SEED_SETTING_DONE BIT(1)
	#define EXYNOS_RNG_STATUS_RNG_DONE BIT(5)

	/* Five seed and output registers, each 4 bytes */
	#define EXYNOS_RNG_SEED_REGS 5
	#define EXYNOS_RNG_SEED_SIZE (EXYNOS_RNG_SEED_REGS * 4)

	enum exynos_prng_type {
	EXYNOS_PRNG_UNKNOWN = 0,
	EXYNOS_PRNG_EXYNOS4,
	EXYNOS_PRNG_EXYNOS5,
	};

	/*
	* Driver re-seeds itself with generated random numbers to hinder
	* backtracking of the original seed.
	*
	* Time for next re-seed in ms.
	*/
	#define EXYNOS_RNG_RESEED_TIME 1000
	#define EXYNOS_RNG_RESEED_BYTES 65536

	/*
	* In polling mode, do not wait infinitely for the engine to finish the work.
	*/
	#define EXYNOS_RNG_WAIT_RETRIES 100

	/* Context for crypto */
	struct exynos_rng_ctx {
	struct exynos_rng_dev *rng;
	};

	/* Device associated memory */
	struct exynos_rng_dev {
	struct device *dev;
	enum exynos_prng_type type;
	void __iomem *mem;
	struct clk *clk;
	struct mutex lock;
	/* Generated numbers stored for seeding during resume */
	u8 seed_save[EXYNOS_RNG_SEED_SIZE];
	unsigned int seed_save_len;
	/* Time of last seeding in jiffies */
	unsigned long last_seeding;
	/* Bytes generated since last seeding */
	unsigned long bytes_seeding;
	};

	static struct exynos_rng_dev *exynos_rng_dev;

	static u32 exynos_rng_readl(struct exynos_rng_dev *rng, u32 offset)
	{
	return readl_relaxed(rng->mem + offset);
	}

	static void exynos_rng_writel(struct exynos_rng_dev *rng, u32 val, u32 offset)
	{
	writel_relaxed(val, rng->mem + offset);
	}

	static int exynos_rng_set_seed(struct exynos_rng_dev *rng,
	const u8 *seed, unsigned int slen)
	{
	u32 val;
	int i;

	/* Round seed length because loop iterates over full register size */
	slen = ALIGN_DOWN(slen, 4);

	if (slen < EXYNOS_RNG_SEED_SIZE)
	return -EINVAL;

	for (i = 0; i < slen ; i += 4) {
	unsigned int seed_reg = (i / 4) % EXYNOS_RNG_SEED_REGS;

	val = seed[i] << 24;
	val \|= seed[i + 1] << 16;
	val \|= seed[i + 2] << 8;
	val \|= seed[i + 3] << 0;

	exynos_rng_writel(rng, val, EXYNOS_RNG_SEED(seed_reg));
	}

	val = exynos_rng_readl(rng, EXYNOS_RNG_STATUS);
	if (!(val & EXYNOS_RNG_STATUS_SEED_SETTING_DONE)) {
	dev_warn(rng->dev, "Seed setting not finished\n");
	return -EIO;
	}

	rng->last_seeding = jiffies;
	rng->bytes_seeding = 0;

	return 0;
	}

	/*
	* Start the engine and poll for finish. Then read from output registers
	* filling the 'dst' buffer up to 'dlen' bytes or up to size of generated
	* random data (EXYNOS_RNG_SEED_SIZE).
	*
	* On success: return 0 and store number of read bytes under 'read' address.
	* On error: return -ERRNO.
	*/
	static int exynos_rng_get_random(struct exynos_rng_dev *rng,
	u8 *dst, unsigned int dlen,
	unsigned int *read)
	{
	int retry = EXYNOS_RNG_WAIT_RETRIES;

	if (rng->type == EXYNOS_PRNG_EXYNOS4) {
	exynos_rng_writel(rng, EXYNOS_RNG_CONTROL_START,
	EXYNOS_RNG_CONTROL);
	} else if (rng->type == EXYNOS_PRNG_EXYNOS5) {
	exynos_rng_writel(rng, EXYNOS_RNG_GEN_PRNG,
	EXYNOS_RNG_SEED_CONF);
	}

	while (!(exynos_rng_readl(rng,
	EXYNOS_RNG_STATUS) & EXYNOS_RNG_STATUS_RNG_DONE) && --retry)
	cpu_relax();

	if (!retry)
	return -ETIMEDOUT;

	/* Clear status bit */
	exynos_rng_writel(rng, EXYNOS_RNG_STATUS_RNG_DONE,
	EXYNOS_RNG_STATUS);
	*read = min_t(size_t, dlen, EXYNOS_RNG_SEED_SIZE);
	memcpy_fromio(dst, rng->mem + EXYNOS_RNG_OUT_BASE, *read);
	rng->bytes_seeding += *read;

	return 0;
	}

	/* Re-seed itself from time to time */
	static void exynos_rng_reseed(struct exynos_rng_dev *rng)
	{
	unsigned long next_seeding = rng->last_seeding + \
	msecs_to_jiffies(EXYNOS_RNG_RESEED_TIME);
	unsigned long now = jiffies;
	unsigned int read = 0;
	u8 seed[EXYNOS_RNG_SEED_SIZE];

	if (time_before(now, next_seeding) &&
	rng->bytes_seeding < EXYNOS_RNG_RESEED_BYTES)
	return;

	if (exynos_rng_get_random(rng, seed, sizeof(seed), &read))
	return;

	exynos_rng_set_seed(rng, seed, read);

	/* Let others do some of their job. */
	mutex_unlock(&rng->lock);
	mutex_lock(&rng->lock);
	}

	static int exynos_rng_generate(struct crypto_rng *tfm,
	const u8 *src, unsigned int slen,
	u8 *dst, unsigned int dlen)
	{
	struct exynos_rng_ctx *ctx = crypto_rng_ctx(tfm);
	struct exynos_rng_dev *rng = ctx->rng;
	unsigned int read = 0;
	int ret;

	ret = clk_prepare_enable(rng->clk);
	if (ret)
	return ret;

	mutex_lock(&rng->lock);
	do {
	ret = exynos_rng_get_random(rng, dst, dlen, &read);
	if (ret)
	break;

	dlen -= read;
	dst += read;

	exynos_rng_reseed(rng);
	} while (dlen > 0);
	mutex_unlock(&rng->lock);

	clk_disable_unprepare(rng->clk);

	return ret;
	}

	static int exynos_rng_seed(struct crypto_rng tfm, const u8 seed,
	unsigned int slen)
	{
	struct exynos_rng_ctx *ctx = crypto_rng_ctx(tfm);
	struct exynos_rng_dev *rng = ctx->rng;
	int ret;

	ret = clk_prepare_enable(rng->clk);
	if (ret)
	return ret;

	mutex_lock(&rng->lock);
	ret = exynos_rng_set_seed(ctx->rng, seed, slen);
	mutex_unlock(&rng->lock);

	clk_disable_unprepare(rng->clk);

	return ret;
	}

	static int exynos_rng_kcapi_init(struct crypto_tfm *tfm)
	{
	struct exynos_rng_ctx *ctx = crypto_tfm_ctx(tfm);

	ctx->rng = exynos_rng_dev;

	return 0;
	}

	static struct rng_alg exynos_rng_alg = {
	.generate = exynos_rng_generate,
	.seed = exynos_rng_seed,
	.seedsize = EXYNOS_RNG_SEED_SIZE,
	.base = {
	.cra_name = "stdrng",
	.cra_driver_name = "exynos_rng",
	.cra_priority = 300,
	.cra_ctxsize = sizeof(struct exynos_rng_ctx),
	.cra_module = THIS_MODULE,
	.cra_init = exynos_rng_kcapi_init,
	}
	};

	static int exynos_rng_probe(struct platform_device *pdev)
	{
	struct exynos_rng_dev *rng;
	struct resource *res;
	int ret;

	if (exynos_rng_dev)
	return -EEXIST;

	rng = devm_kzalloc(&pdev->dev, sizeof(*rng), GFP_KERNEL);
	if (!rng)
	return -ENOMEM;

	rng->type = (enum exynos_prng_type)of_device_get_match_data(&pdev->dev);

	mutex_init(&rng->lock);

	rng->dev = &pdev->dev;
	rng->clk = devm_clk_get(&pdev->dev, "secss");
	if (IS_ERR(rng->clk)) {
	dev_err(&pdev->dev, "Couldn't get clock.\n");
	return PTR_ERR(rng->clk);
	}

	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
	rng->mem = devm_ioremap_resource(&pdev->dev, res);
	if (IS_ERR(rng->mem))
	return PTR_ERR(rng->mem);

	platform_set_drvdata(pdev, rng);

	exynos_rng_dev = rng;

	ret = crypto_register_rng(&exynos_rng_alg);
	if (ret) {
	dev_err(&pdev->dev,
	"Couldn't register rng crypto alg: %d\n", ret);
	exynos_rng_dev = NULL;
	}

	return ret;
	}

	static int exynos_rng_remove(struct platform_device *pdev)
	{
	crypto_unregister_rng(&exynos_rng_alg);

	exynos_rng_dev = NULL;

	return 0;
	}

	static int __maybe_unused exynos_rng_suspend(struct device *dev)
	{
	struct platform_device *pdev = to_platform_device(dev);
	struct exynos_rng_dev *rng = platform_get_drvdata(pdev);
	int ret;

	/* If we were never seeded then after resume it will be the same */
	if (!rng->last_seeding)
	return 0;

	rng->seed_save_len = 0;
	ret = clk_prepare_enable(rng->clk);
	if (ret)
	return ret;

	mutex_lock(&rng->lock);

	/* Get new random numbers and store them for seeding on resume. */
	exynos_rng_get_random(rng, rng->seed_save, sizeof(rng->seed_save),
	&(rng->seed_save_len));

	mutex_unlock(&rng->lock);

	dev_dbg(rng->dev, "Stored %u bytes for seeding on system resume\n",
	rng->seed_save_len);

	clk_disable_unprepare(rng->clk);

	return 0;
	}

	static int __maybe_unused exynos_rng_resume(struct device *dev)
	{
	struct platform_device *pdev = to_platform_device(dev);
	struct exynos_rng_dev *rng = platform_get_drvdata(pdev);
	int ret;

	/* Never seeded so nothing to do */
	if (!rng->last_seeding)
	return 0;

	ret = clk_prepare_enable(rng->clk);
	if (ret)
	return ret;

	mutex_lock(&rng->lock);

	ret = exynos_rng_set_seed(rng, rng->seed_save, rng->seed_save_len);

	mutex_unlock(&rng->lock);

	clk_disable_unprepare(rng->clk);

	return ret;
	}

	static SIMPLE_DEV_PM_OPS(exynos_rng_pm_ops, exynos_rng_suspend,
	exynos_rng_resume);

	static const struct of_device_id exynos_rng_dt_match[] = {
	{
	.compatible = "samsung,exynos4-rng",
	.data = (const void *)EXYNOS_PRNG_EXYNOS4,
	}, {
	.compatible = "samsung,exynos5250-prng",
	.data = (const void *)EXYNOS_PRNG_EXYNOS5,
	},
	{ },
	};
	MODULE_DEVICE_TABLE(of, exynos_rng_dt_match);

	static struct platform_driver exynos_rng_driver = {
	.driver = {
	.name = "exynos-rng",
	.pm = &exynos_rng_pm_ops,
	.of_match_table = exynos_rng_dt_match,
	},
	.probe = exynos_rng_probe,
	.remove = exynos_rng_remove,
	};

	module_platform_driver(exynos_rng_driver);

	MODULE_DESCRIPTION("Exynos H/W Random Number Generator driver");
	MODULE_AUTHOR("Krzysztof Kozlowski <krzk@kernel.org>");
	MODULE_LICENSE("GPL v2");