drivers/char/hw_random/exynos-trng.c

// SPDX-License-Identifier: GPL-2.0
/*
 * RNG driver for Exynos TRNGs
 *
 * Author: Łukasz Stelmach <l.stelmach@samsung.com>
 *
 * Copyright 2017 (c) Samsung Electronics Software, Inc.
 *
 * Based on the Exynos PRNG driver drivers/crypto/exynos-rng by
 * Krzysztof Kozłowski <krzk@kernel.org>
 */

#include <linux/arm-smccc.h>
#include <linux/clk.h>
#include <linux/crypto.h>
#include <linux/delay.h>
#include <linux/err.h>
#include <linux/hw_random.h>
#include <linux/io.h>
#include <linux/iopoll.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/pm_runtime.h>
#include <linux/property.h>

#define EXYNOS_TRNG_CLKDIV		0x0

#define EXYNOS_TRNG_CTRL		0x20
#define EXYNOS_TRNG_CTRL_RNGEN		BIT(31)

#define EXYNOS_TRNG_POST_CTRL		0x30
#define EXYNOS_TRNG_ONLINE_CTRL		0x40
#define EXYNOS_TRNG_ONLINE_STAT		0x44
#define EXYNOS_TRNG_ONLINE_MAXCHI2	0x48
#define EXYNOS_TRNG_FIFO_CTRL		0x50
#define EXYNOS_TRNG_FIFO_0		0x80
#define EXYNOS_TRNG_FIFO_1		0x84
#define EXYNOS_TRNG_FIFO_2		0x88
#define EXYNOS_TRNG_FIFO_3		0x8c
#define EXYNOS_TRNG_FIFO_4		0x90
#define EXYNOS_TRNG_FIFO_5		0x94
#define EXYNOS_TRNG_FIFO_6		0x98
#define EXYNOS_TRNG_FIFO_7		0x9c
#define EXYNOS_TRNG_FIFO_LEN		8
#define EXYNOS_TRNG_CLOCK_RATE		500000

/* Driver feature flags */
#define EXYNOS_SMC			BIT(0)

#define EXYNOS_SMC_CALL_VAL(func_num)			\
	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,		\
			   ARM_SMCCC_SMC_32,		\
			   ARM_SMCCC_OWNER_SIP,		\
			   func_num)

/* SMC command for DTRNG access */
#define SMC_CMD_RANDOM			EXYNOS_SMC_CALL_VAL(0x1012)

/* SMC_CMD_RANDOM: arguments */
#define HWRNG_INIT			0x0
#define HWRNG_EXIT			0x1
#define HWRNG_GET_DATA			0x2
#define HWRNG_RESUME			0x3

/* SMC_CMD_RANDOM: return values */
#define HWRNG_RET_OK			0x0
#define HWRNG_RET_RETRY_ERROR		0x2

#define HWRNG_MAX_TRIES			100

struct exynos_trng_dev {
	struct device	*dev;
	void __iomem	*mem;
	struct clk	*clk;	/* operating clock */
	struct clk	*pclk;	/* bus clock */
	struct hwrng	rng;
	unsigned long	flags;
};

static int exynos_trng_do_read_reg(struct hwrng *rng, void *data, size_t max,
				   bool wait)
{
	struct exynos_trng_dev *trng = (struct exynos_trng_dev *)rng->priv;
	int val;

	max = min_t(size_t, max, (EXYNOS_TRNG_FIFO_LEN * 4));
	writel_relaxed(max * 8, trng->mem + EXYNOS_TRNG_FIFO_CTRL);
	val = readl_poll_timeout(trng->mem + EXYNOS_TRNG_FIFO_CTRL, val,
				 val == 0, 200, 1000000);
	if (val < 0)
		return val;

	memcpy_fromio(data, trng->mem + EXYNOS_TRNG_FIFO_0, max);

	return max;
}

static int exynos_trng_do_read_smc(struct hwrng *rng, void *data, size_t max,
				   bool wait)
{
	struct arm_smccc_res res;
	unsigned int copied = 0;
	u32 *buf = data;
	int tries = 0;

	while (copied < max) {
		arm_smccc_smc(SMC_CMD_RANDOM, HWRNG_GET_DATA, 0, 0, 0, 0, 0, 0,
			      &res);
		switch (res.a0) {
		case HWRNG_RET_OK:
			*buf++ = res.a2;
			*buf++ = res.a3;
			copied += 8;
			tries = 0;
			break;
		case HWRNG_RET_RETRY_ERROR:
			if (!wait)
				return copied;
			if (++tries >= HWRNG_MAX_TRIES)
				return copied;
			cond_resched();
			break;
		default:
			return -EIO;
		}
	}

	return copied;
}

static int exynos_trng_init_reg(struct hwrng *rng)
{
	struct exynos_trng_dev *trng = (struct exynos_trng_dev *)rng->priv;
	unsigned long sss_rate;
	u32 val;

	sss_rate = clk_get_rate(trng->clk);

	/*
	 * For most TRNG circuits the clock frequency of under 500 kHz
	 * is safe.
	 */
	val = sss_rate / (EXYNOS_TRNG_CLOCK_RATE * 2);
	if (val > 0x7fff) {
		dev_err(trng->dev, "clock divider too large: %d\n", val);
		return -ERANGE;
	}
	val = val << 1;
	writel_relaxed(val, trng->mem + EXYNOS_TRNG_CLKDIV);

	/* Enable the generator. */
	val = EXYNOS_TRNG_CTRL_RNGEN;
	writel_relaxed(val, trng->mem + EXYNOS_TRNG_CTRL);

	/*
	 * Disable post-processing. /dev/hwrng is supposed to deliver
	 * unprocessed data.
	 */
	writel_relaxed(0, trng->mem + EXYNOS_TRNG_POST_CTRL);

	return 0;
}

static int exynos_trng_init_smc(struct hwrng *rng)
{
	struct exynos_trng_dev *trng = (struct exynos_trng_dev *)rng->priv;
	struct arm_smccc_res res;
	int ret = 0;

	arm_smccc_smc(SMC_CMD_RANDOM, HWRNG_INIT, 0, 0, 0, 0, 0, 0, &res);
	if (res.a0 != HWRNG_RET_OK) {
		dev_err(trng->dev, "SMC command for TRNG init failed (%d)\n",
			(int)res.a0);
		ret = -EIO;
	}
	if ((int)res.a0 == -1)
		dev_info(trng->dev, "Make sure LDFW is loaded by your BL\n");

	return ret;
}

static int exynos_trng_probe(struct platform_device *pdev)
{
	struct exynos_trng_dev *trng;
	int ret = -ENOMEM;

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

	platform_set_drvdata(pdev, trng);
	trng->dev = &pdev->dev;

	trng->flags = (unsigned long)device_get_match_data(&pdev->dev);

	trng->rng.name = devm_kstrdup(&pdev->dev, dev_name(&pdev->dev),
				      GFP_KERNEL);
	if (!trng->rng.name)
		return ret;

	trng->rng.priv = (unsigned long)trng;

	if (trng->flags & EXYNOS_SMC) {
		trng->rng.init = exynos_trng_init_smc;
		trng->rng.read = exynos_trng_do_read_smc;
	} else {
		trng->rng.init = exynos_trng_init_reg;
		trng->rng.read = exynos_trng_do_read_reg;

		trng->mem = devm_platform_ioremap_resource(pdev, 0);
		if (IS_ERR(trng->mem))
			return PTR_ERR(trng->mem);
	}

	pm_runtime_enable(&pdev->dev);
	ret = pm_runtime_resume_and_get(&pdev->dev);
	if (ret < 0) {
		dev_err(&pdev->dev, "Could not get runtime PM.\n");
		goto err_pm_get;
	}

	trng->clk = devm_clk_get_enabled(&pdev->dev, "secss");
	if (IS_ERR(trng->clk)) {
		ret = dev_err_probe(&pdev->dev, PTR_ERR(trng->clk),
				    "Could not get clock\n");
		goto err_clock;
	}

	trng->pclk = devm_clk_get_optional_enabled(&pdev->dev, "pclk");
	if (IS_ERR(trng->pclk)) {
		ret = dev_err_probe(&pdev->dev, PTR_ERR(trng->pclk),
				    "Could not get pclk\n");
		goto err_clock;
	}

	ret = devm_hwrng_register(&pdev->dev, &trng->rng);
	if (ret) {
		dev_err(&pdev->dev, "Could not register hwrng device.\n");
		goto err_clock;
	}

	dev_info(&pdev->dev, "Exynos True Random Number Generator.\n");

	return 0;

err_clock:
	pm_runtime_put_noidle(&pdev->dev);

err_pm_get:
	pm_runtime_disable(&pdev->dev);

	return ret;
}

static void exynos_trng_remove(struct platform_device *pdev)
{
	struct exynos_trng_dev *trng = platform_get_drvdata(pdev);

	if (trng->flags & EXYNOS_SMC) {
		struct arm_smccc_res res;

		arm_smccc_smc(SMC_CMD_RANDOM, HWRNG_EXIT, 0, 0, 0, 0, 0, 0,
			      &res);
	}

	pm_runtime_put_sync(&pdev->dev);
	pm_runtime_disable(&pdev->dev);
}

static int exynos_trng_suspend(struct device *dev)
{
	struct exynos_trng_dev *trng = dev_get_drvdata(dev);
	struct arm_smccc_res res;

	if (trng->flags & EXYNOS_SMC) {
		arm_smccc_smc(SMC_CMD_RANDOM, HWRNG_EXIT, 0, 0, 0, 0, 0, 0,
			      &res);
		if (res.a0 != HWRNG_RET_OK)
			return -EIO;
	}

	pm_runtime_put_sync(dev);

	return 0;
}

static int exynos_trng_resume(struct device *dev)
{
	struct exynos_trng_dev *trng = dev_get_drvdata(dev);
	int ret;

	ret = pm_runtime_resume_and_get(dev);
	if (ret < 0) {
		dev_err(dev, "Could not get runtime PM.\n");
		return ret;
	}

	if (trng->flags & EXYNOS_SMC) {
		struct arm_smccc_res res;

		arm_smccc_smc(SMC_CMD_RANDOM, HWRNG_RESUME, 0, 0, 0, 0, 0, 0,
			      &res);
		if (res.a0 != HWRNG_RET_OK)
			return -EIO;

		arm_smccc_smc(SMC_CMD_RANDOM, HWRNG_INIT, 0, 0, 0, 0, 0, 0,
			      &res);
		if (res.a0 != HWRNG_RET_OK)
			return -EIO;
	}

	return 0;
}

static DEFINE_SIMPLE_DEV_PM_OPS(exynos_trng_pm_ops, exynos_trng_suspend,
				exynos_trng_resume);

static const struct of_device_id exynos_trng_dt_match[] = {
	{
		.compatible = "samsung,exynos5250-trng",
	}, {
		.compatible = "samsung,exynos850-trng",
		.data = (void *)EXYNOS_SMC,
	},
	{ },
};
MODULE_DEVICE_TABLE(of, exynos_trng_dt_match);

static struct platform_driver exynos_trng_driver = {
	.driver = {
		.name = "exynos-trng",
		.pm = pm_sleep_ptr(&exynos_trng_pm_ops),
		.of_match_table = exynos_trng_dt_match,
	},
	.probe = exynos_trng_probe,
	.remove = exynos_trng_remove,
};

module_platform_driver(exynos_trng_driver);

MODULE_AUTHOR("Łukasz Stelmach");
MODULE_DESCRIPTION("H/W TRNG driver for Exynos chips");
MODULE_LICENSE("GPL v2");