// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Nomadik RNG support
 *  Copyright 2009 Alessandro Rubini
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/device.h>
#include <linux/amba/bus.h>
#include <linux/hw_random.h>
#include <linux/io.h>
#include <linux/clk.h>
#include <linux/err.h>

static int nmk_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
{
        void __iomem *base = (void __iomem *)rng->priv;

        /*
         * The register is 32 bits and gives 16 random bits (low half).
         * A subsequent read will delay the core for 400ns, so we just read
         * once and accept the very unlikely very small delay, even if wait==0.
         */
        *(u16 *)data = __raw_readl(base + 8) & 0xffff;
        return 2;
}

/* we have at most one RNG per machine, granted */
static struct hwrng nmk_rng = {
        .name           = "nomadik",
        .read           = nmk_rng_read,
};

static int nmk_rng_probe(struct amba_device *dev, const struct amba_id *id)
{
        struct clk *rng_clk;
        void __iomem *base;
        int ret;

        rng_clk = devm_clk_get_enabled(&dev->dev, NULL);
        if (IS_ERR(rng_clk))
                return dev_err_probe(&dev->dev, PTR_ERR(rng_clk), "could not get rng clock\n");

        ret = amba_request_regions(dev, dev->dev.init_name);
        if (ret)
                return ret;
        ret = -ENOMEM;
        base = devm_ioremap(&dev->dev, dev->res.start,
                            resource_size(&dev->res));
        if (!base)
                goto out_release;
        nmk_rng.priv = (unsigned long)base;
        ret = devm_hwrng_register(&dev->dev, &nmk_rng);
        if (ret)
                goto out_release;
        return 0;

out_release:
        amba_release_regions(dev);
        return ret;
}

static void nmk_rng_remove(struct amba_device *dev)
{
        amba_release_regions(dev);
}

static const struct amba_id nmk_rng_ids[] = {
        {
                .id     = 0x000805e1,
                .mask   = 0x000fffff, /* top bits are rev and cfg: accept all */
        },
        {0, 0},
};

MODULE_DEVICE_TABLE(amba, nmk_rng_ids);

static struct amba_driver nmk_rng_driver = {
        .drv = {
                .name = "rng",
                },
        .probe = nmk_rng_probe,
        .remove = nmk_rng_remove,
        .id_table = nmk_rng_ids,
};

module_amba_driver(nmk_rng_driver);

MODULE_DESCRIPTION("ST-Ericsson Nomadik Random Number Generator");
MODULE_LICENSE("GPL");