/**
 * Copyright (c) 2010-2012 Broadcom. All rights reserved.
 * Copyright (c) 2013 Lubomir Rintel
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License ("GPL")
 * version 2, as published by the Free Software Foundation.
 */

#include <linux/hw_random.h>
#include <linux/io.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/of_address.h>
#include <linux/of_platform.h>
#include <linux/platform_device.h>
#include <linux/printk.h>
#include <linux/clk.h>

#define RNG_CTRL        0x0
#define RNG_STATUS      0x4
#define RNG_DATA        0x8
#define RNG_INT_MASK    0x10

/* enable rng */
#define RNG_RBGEN       0x1

/* the initial numbers generated are "less random" so will be discarded */
#define RNG_WARMUP_COUNT 0x40000

#define RNG_INT_OFF     0x1

struct bcm2835_rng_priv {
        struct hwrng rng;
        void __iomem *base;
        bool mask_interrupts;
        struct clk *clk;
};

static inline struct bcm2835_rng_priv *to_rng_priv(struct hwrng *rng)
{
        return container_of(rng, struct bcm2835_rng_priv, rng);
}

static inline u32 rng_readl(struct bcm2835_rng_priv *priv, u32 offset)
{
        /* MIPS chips strapped for BE will automagically configure the
         * peripheral registers for CPU-native byte order.
         */
        if (IS_ENABLED(CONFIG_MIPS) && IS_ENABLED(CONFIG_CPU_BIG_ENDIAN))
                return __raw_readl(priv->base + offset);
        else
                return readl(priv->base + offset);
}

static inline void rng_writel(struct bcm2835_rng_priv *priv, u32 val,
                              u32 offset)
{
        if (IS_ENABLED(CONFIG_MIPS) && IS_ENABLED(CONFIG_CPU_BIG_ENDIAN))
                __raw_writel(val, priv->base + offset);
        else
                writel(val, priv->base + offset);
}

static int bcm2835_rng_read(struct hwrng *rng, void *buf, size_t max,
                               bool wait)
{
        struct bcm2835_rng_priv *priv = to_rng_priv(rng);
        u32 max_words = max / sizeof(u32);
        u32 num_words, count;

        while ((rng_readl(priv, RNG_STATUS) >> 24) == 0) {
                if (!wait)
                        return 0;
                cpu_relax();
        }

        num_words = rng_readl(priv, RNG_STATUS) >> 24;
        if (num_words > max_words)
                num_words = max_words;

        for (count = 0; count < num_words; count++)
                ((u32 *)buf)[count] = rng_readl(priv, RNG_DATA);

        return num_words * sizeof(u32);
}

static int bcm2835_rng_init(struct hwrng *rng)
{
        struct bcm2835_rng_priv *priv = to_rng_priv(rng);
        int ret = 0;
        u32 val;

        if (!IS_ERR(priv->clk)) {
                ret = clk_prepare_enable(priv->clk);
                if (ret)
                        return ret;
        }

        if (priv->mask_interrupts) {
                /* mask the interrupt */
                val = rng_readl(priv, RNG_INT_MASK);
                val |= RNG_INT_OFF;
                rng_writel(priv, val, RNG_INT_MASK);
        }

        /* set warm-up count & enable */
        rng_writel(priv, RNG_WARMUP_COUNT, RNG_STATUS);
        rng_writel(priv, RNG_RBGEN, RNG_CTRL);

        return ret;
}

static void bcm2835_rng_cleanup(struct hwrng *rng)
{
        struct bcm2835_rng_priv *priv = to_rng_priv(rng);

        /* disable rng hardware */
        rng_writel(priv, 0, RNG_CTRL);

        if (!IS_ERR(priv->clk))
                clk_disable_unprepare(priv->clk);
}

struct bcm2835_rng_of_data {
        bool mask_interrupts;
};

static const struct bcm2835_rng_of_data nsp_rng_of_data = {
        .mask_interrupts = true,
};

static const struct of_device_id bcm2835_rng_of_match[] = {
        { .compatible = "brcm,bcm2835-rng"},
        { .compatible = "brcm,bcm-nsp-rng", .data = &nsp_rng_of_data },
        { .compatible = "brcm,bcm5301x-rng", .data = &nsp_rng_of_data },
        { .compatible = "brcm,bcm6368-rng"},
        {},
};

static int bcm2835_rng_probe(struct platform_device *pdev)
{
        const struct bcm2835_rng_of_data *of_data;
        struct device *dev = &pdev->dev;
        struct device_node *np = dev->of_node;
        const struct of_device_id *rng_id;
        struct bcm2835_rng_priv *priv;
        struct resource *r;
        int err;

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

        platform_set_drvdata(pdev, priv);

        r = platform_get_resource(pdev, IORESOURCE_MEM, 0);

        /* map peripheral */
        priv->base = devm_ioremap_resource(dev, r);
        if (IS_ERR(priv->base))
                return PTR_ERR(priv->base);

        /* Clock is optional on most platforms */
        priv->clk = devm_clk_get(dev, NULL);
        if (IS_ERR(priv->clk) && PTR_ERR(priv->clk) == -EPROBE_DEFER)
                return -EPROBE_DEFER;

        priv->rng.name = pdev->name;
        priv->rng.init = bcm2835_rng_init;
        priv->rng.read = bcm2835_rng_read;
        priv->rng.cleanup = bcm2835_rng_cleanup;

        rng_id = of_match_node(bcm2835_rng_of_match, np);
        if (!rng_id)
                return -EINVAL;

        /* Check for rng init function, execute it */
        of_data = rng_id->data;
        if (of_data)
                priv->mask_interrupts = of_data->mask_interrupts;

        /* register driver */
        err = devm_hwrng_register(dev, &priv->rng);
        if (err)
                dev_err(dev, "hwrng registration failed\n");
        else
                dev_info(dev, "hwrng registered\n");

        return err;
}

MODULE_DEVICE_TABLE(of, bcm2835_rng_of_match);

static struct platform_device_id bcm2835_rng_devtype[] = {
        { .name = "bcm2835-rng" },
        { .name = "bcm63xx-rng" },
        { /* sentinel */ }
};
MODULE_DEVICE_TABLE(platform, bcm2835_rng_devtype);

static struct platform_driver bcm2835_rng_driver = {
        .driver = {
                .name = "bcm2835-rng",
                .of_match_table = bcm2835_rng_of_match,
        },
        .probe          = bcm2835_rng_probe,
        .id_table       = bcm2835_rng_devtype,
};
module_platform_driver(bcm2835_rng_driver);

MODULE_AUTHOR("Lubomir Rintel <lkundrak@v3.sk>");
MODULE_DESCRIPTION("BCM2835 Random Number Generator (RNG) driver");
MODULE_LICENSE("GPL v2");