// SPDX-License-Identifier: GPL-2.0
// Copyright (c) 2020 Silex Insight

#include <linux/delay.h>
#include <linux/hw_random.h>
#include <linux/io.h>
#include <linux/iopoll.h>
#include <linux/kernel.h>
#include <linux/mod_devicetable.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/workqueue.h>

#define BA431_RESET_DELAY                       1 /* usec */
#define BA431_RESET_READ_STATUS_TIMEOUT         1000 /* usec */
#define BA431_RESET_READ_STATUS_INTERVAL        10 /* usec */
#define BA431_READ_RETRY_INTERVAL               1 /* usec */

#define BA431_REG_CTRL                          0x00
#define BA431_REG_FIFO_LEVEL                    0x04
#define BA431_REG_STATUS                        0x30
#define BA431_REG_FIFODATA                      0x80

#define BA431_CTRL_ENABLE                       BIT(0)
#define BA431_CTRL_SOFTRESET                    BIT(8)

#define BA431_STATUS_STATE_MASK                 (BIT(1) | BIT(2) | BIT(3))
#define BA431_STATUS_STATE_OFFSET               1

enum ba431_state {
        BA431_STATE_RESET,
        BA431_STATE_STARTUP,
        BA431_STATE_FIFOFULLON,
        BA431_STATE_FIFOFULLOFF,
        BA431_STATE_RUNNING,
        BA431_STATE_ERROR
};

struct ba431_trng {
        struct device *dev;
        void __iomem *base;
        struct hwrng rng;
        atomic_t reset_pending;
        struct work_struct reset_work;
};

static inline u32 ba431_trng_read_reg(struct ba431_trng *ba431, u32 reg)
{
        return ioread32(ba431->base + reg);
}

static inline void ba431_trng_write_reg(struct ba431_trng *ba431, u32 reg,
                                        u32 val)
{
        iowrite32(val, ba431->base + reg);
}

static inline enum ba431_state ba431_trng_get_state(struct ba431_trng *ba431)
{
        u32 status = ba431_trng_read_reg(ba431, BA431_REG_STATUS);

        return (status & BA431_STATUS_STATE_MASK) >> BA431_STATUS_STATE_OFFSET;
}

static int ba431_trng_is_in_error(struct ba431_trng *ba431)
{
        enum ba431_state state = ba431_trng_get_state(ba431);

        if ((state < BA431_STATE_STARTUP) ||
            (state >= BA431_STATE_ERROR))
                return 1;

        return 0;
}

static int ba431_trng_reset(struct ba431_trng *ba431)
{
        int ret;

        /* Disable interrupts, random generation and enable the softreset */
        ba431_trng_write_reg(ba431, BA431_REG_CTRL, BA431_CTRL_SOFTRESET);
        udelay(BA431_RESET_DELAY);
        ba431_trng_write_reg(ba431, BA431_REG_CTRL, BA431_CTRL_ENABLE);

        /* Wait until the state changed */
        if (readx_poll_timeout(ba431_trng_is_in_error, ba431, ret, !ret,
                               BA431_RESET_READ_STATUS_INTERVAL,
                               BA431_RESET_READ_STATUS_TIMEOUT)) {
                dev_err(ba431->dev, "reset failed (state: %d)\n",
                        ba431_trng_get_state(ba431));
                return -ETIMEDOUT;
        }

        dev_info(ba431->dev, "reset done\n");

        return 0;
}

static void ba431_trng_reset_work(struct work_struct *work)
{
        struct ba431_trng *ba431 = container_of(work, struct ba431_trng,
                                                reset_work);
        ba431_trng_reset(ba431);
        atomic_set(&ba431->reset_pending, 0);
}

static void ba431_trng_schedule_reset(struct ba431_trng *ba431)
{
        if (atomic_cmpxchg(&ba431->reset_pending, 0, 1))
                return;

        schedule_work(&ba431->reset_work);
}

static int ba431_trng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
{
        struct ba431_trng *ba431 = container_of(rng, struct ba431_trng, rng);
        u32 *data = buf;
        unsigned int level, i;
        int n = 0;

        while (max > 0) {
                level = ba431_trng_read_reg(ba431, BA431_REG_FIFO_LEVEL);
                if (!level) {
                        if (ba431_trng_is_in_error(ba431)) {
                                ba431_trng_schedule_reset(ba431);
                                break;
                        }

                        if (!wait)
                                break;

                        udelay(BA431_READ_RETRY_INTERVAL);
                        continue;
                }

                i = level;
                do {
                        data[n++] = ba431_trng_read_reg(ba431,
                                                        BA431_REG_FIFODATA);
                        max -= sizeof(*data);
                } while (--i && (max > 0));

                if (ba431_trng_is_in_error(ba431)) {
                        n -= (level - i);
                        ba431_trng_schedule_reset(ba431);
                        break;
                }
        }

        n *= sizeof(data);
        return (n || !wait) ? n : -EIO;
}

static void ba431_trng_cleanup(struct hwrng *rng)
{
        struct ba431_trng *ba431 = container_of(rng, struct ba431_trng, rng);

        ba431_trng_write_reg(ba431, BA431_REG_CTRL, 0);
        cancel_work_sync(&ba431->reset_work);
}

static int ba431_trng_init(struct hwrng *rng)
{
        struct ba431_trng *ba431 = container_of(rng, struct ba431_trng, rng);

        return ba431_trng_reset(ba431);
}

static int ba431_trng_probe(struct platform_device *pdev)
{
        struct ba431_trng *ba431;
        int ret;

        ba431 = devm_kzalloc(&pdev->dev, sizeof(*ba431), GFP_KERNEL);
        if (!ba431)
                return -ENOMEM;

        ba431->dev = &pdev->dev;

        ba431->base = devm_platform_ioremap_resource(pdev, 0);
        if (IS_ERR(ba431->base))
                return PTR_ERR(ba431->base);

        atomic_set(&ba431->reset_pending, 0);
        INIT_WORK(&ba431->reset_work, ba431_trng_reset_work);
        ba431->rng.name = pdev->name;
        ba431->rng.init = ba431_trng_init;
        ba431->rng.cleanup = ba431_trng_cleanup;
        ba431->rng.read = ba431_trng_read;

        ret = devm_hwrng_register(&pdev->dev, &ba431->rng);
        if (ret)
                return dev_err_probe(&pdev->dev, ret, "BA431 registration failed\n");

        dev_info(&pdev->dev, "BA431 TRNG registered\n");

        return 0;
}

static const struct of_device_id ba431_trng_dt_ids[] = {
        { .compatible = "silex-insight,ba431-rng" },
        { /* sentinel */ }
};
MODULE_DEVICE_TABLE(of, ba431_trng_dt_ids);

static struct platform_driver ba431_trng_driver = {
        .driver = {
                .name = "ba431-rng",
                .of_match_table = ba431_trng_dt_ids,
        },
        .probe = ba431_trng_probe,
};

module_platform_driver(ba431_trng_driver);

MODULE_AUTHOR("Olivier Sobrie <olivier@sobrie.be>");
MODULE_DESCRIPTION("TRNG driver for Silex Insight BA431");
MODULE_LICENSE("GPL");