nomadik-rng.c

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/*
 * Nomadik RNG support
 *  Copyright 2009 Alessandro Rubini
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.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 struct clk *rng_clk;

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)
{
    void __iomem *base;
    int ret;

    rng_clk = clk_get(&dev->dev, NULL);
    if (IS_ERR(rng_clk)) {
        dev_err(&dev->dev, "could not get rng clock\n");
        ret = PTR_ERR(rng_clk);
        return ret;
    }

    clk_enable(rng_clk);

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

out_unmap:
    iounmap(base);
out_release:
    amba_release_regions(dev);
out_clk:
    clk_disable(rng_clk);
    clk_put(rng_clk);
    return ret;
}

static int nmk_rng_remove(struct amba_device *dev)
{
    void __iomem *base = (void __iomem *)nmk_rng.priv;
    hwrng_unregister(&nmk_rng);
    iounmap(base);
    amba_release_regions(dev);
    clk_disable(rng_clk);
    clk_put(rng_clk);
    return 0;
}

static 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 = {
        .owner = THIS_MODULE,
        .name = "rng",
        },
    .probe = nmk_rng_probe,
    .remove = nmk_rng_remove,
    .id_table = nmk_rng_ids,
};

module_amba_driver(nmk_rng_driver);

MODULE_LICENSE("GPL");