// SPDX-License-Identifier: GPL-2.0-only
/*
 * PIC32 RNG driver
 *
 * Joshua Henderson <joshua.henderson@microchip.com>
 * Copyright (C) 2016 Microchip Technology Inc.  All rights reserved.
 */

#include <linux/clk.h>
#include <linux/clkdev.h>
#include <linux/err.h>
#include <linux/hw_random.h>
#include <linux/io.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/slab.h>

#define RNGCON          0x04
#define TRNGEN          BIT(8)
#define TRNGMOD         BIT(11)
#define RNGSEED1        0x18
#define RNGSEED2        0x1C
#define RNGRCNT         0x20
#define RCNT_MASK       0x7F

struct pic32_rng {
        void __iomem    *base;
        struct hwrng    rng;
};

/*
 * The TRNG can generate up to 24Mbps. This is a timeout that should be safe
 * enough given the instructions in the loop and that the TRNG may not always
 * be at maximum rate.
 */
#define RNG_TIMEOUT 500

static int pic32_rng_init(struct hwrng *rng)
{
        struct pic32_rng *priv = container_of(rng, struct pic32_rng, rng);

        /* enable TRNG in enhanced mode */
        writel(TRNGEN | TRNGMOD, priv->base + RNGCON);
        return 0;
}

static int pic32_rng_read(struct hwrng *rng, void *buf, size_t max,
                          bool wait)
{
        struct pic32_rng *priv = container_of(rng, struct pic32_rng, rng);
        u64 *data = buf;
        u32 t;
        unsigned int timeout = RNG_TIMEOUT;

        do {
                t = readl(priv->base + RNGRCNT) & RCNT_MASK;
                if (t == 64) {
                        /* TRNG value comes through the seed registers */
                        *data = ((u64)readl(priv->base + RNGSEED2) << 32) +
                                readl(priv->base + RNGSEED1);
                        return 8;
                }
        } while (wait && --timeout);

        return -EIO;
}

static void pic32_rng_cleanup(struct hwrng *rng)
{
        struct pic32_rng *priv = container_of(rng, struct pic32_rng, rng);

        writel(0, priv->base + RNGCON);
}

static int pic32_rng_probe(struct platform_device *pdev)
{
        struct pic32_rng *priv;
        struct clk *clk;

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

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

        clk = devm_clk_get_enabled(&pdev->dev, NULL);
        if (IS_ERR(clk))
                return PTR_ERR(clk);

        priv->rng.name = pdev->name;
        priv->rng.init = pic32_rng_init;
        priv->rng.read = pic32_rng_read;
        priv->rng.cleanup = pic32_rng_cleanup;

        return devm_hwrng_register(&pdev->dev, &priv->rng);
}

static const struct of_device_id pic32_rng_of_match[] __maybe_unused = {
        { .compatible   = "microchip,pic32mzda-rng", },
        { /* sentinel */ }
};
MODULE_DEVICE_TABLE(of, pic32_rng_of_match);

static struct platform_driver pic32_rng_driver = {
        .probe          = pic32_rng_probe,
        .driver         = {
                .name   = "pic32-rng",
                .of_match_table = pic32_rng_of_match,
        },
};

module_platform_driver(pic32_rng_driver);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Joshua Henderson <joshua.henderson@microchip.com>");
MODULE_DESCRIPTION("Microchip PIC32 RNG Driver");