// 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.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;
        int ret;

        if (exynos_rng_dev)
                return -EEXIST;

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

        rng->type = (uintptr_t)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);
        }

        rng->mem = devm_platform_ioremap_resource(pdev, 0);
        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 void exynos_rng_remove(struct platform_device *pdev)
{
        crypto_unregister_rng(&exynos_rng_alg);

        exynos_rng_dev = NULL;
}

static int __maybe_unused exynos_rng_suspend(struct device *dev)
{
        struct exynos_rng_dev *rng = dev_get_drvdata(dev);
        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 exynos_rng_dev *rng = dev_get_drvdata(dev);
        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");