/*
 * Copyright (c) 2011 Peter Korsgaard <jacmet@sunsite.dk>
 *
 * This file is licensed under  the terms of the GNU General Public
 * License version 2. This program is licensed "as is" without any
 * warranty of any kind, whether express or implied.
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/mod_devicetable.h>
#include <linux/slab.h>
#include <linux/err.h>
#include <linux/clk.h>
#include <linux/io.h>
#include <linux/iopoll.h>
#include <linux/hw_random.h>
#include <linux/of.h>
#include <linux/platform_device.h>
#include <linux/pm_runtime.h>

#define TRNG_CR         0x00
#define TRNG_MR         0x04
#define TRNG_ISR        0x1c
#define TRNG_ISR_DATRDY BIT(0)
#define TRNG_ODATA      0x50

#define TRNG_KEY        0x524e4700 /* RNG */

#define TRNG_HALFR      BIT(0) /* generate RN every 168 cycles */

struct atmel_trng_data {
        bool has_half_rate;
};

struct atmel_trng {
        struct clk *clk;
        void __iomem *base;
        struct hwrng rng;
        struct device *dev;
        bool has_half_rate;
};

static bool atmel_trng_wait_ready(struct atmel_trng *trng, bool wait)
{
        int ready;

        ready = readl(trng->base + TRNG_ISR) & TRNG_ISR_DATRDY;
        if (!ready && wait)
                readl_poll_timeout(trng->base + TRNG_ISR, ready,
                                   ready & TRNG_ISR_DATRDY, 1000, 20000);

        return !!ready;
}

static int atmel_trng_read(struct hwrng *rng, void *buf, size_t max,
                           bool wait)
{
        struct atmel_trng *trng = container_of(rng, struct atmel_trng, rng);
        u32 *data = buf;
        int ret;

        ret = pm_runtime_get_sync(trng->dev);
        if (ret < 0) {
                pm_runtime_put_sync(trng->dev);
                return ret;
        }

        ret = atmel_trng_wait_ready(trng, wait);
        if (!ret)
                goto out;

        *data = readl(trng->base + TRNG_ODATA);
        /*
         * ensure data ready is only set again AFTER the next data word is ready
         * in case it got set between checking ISR and reading ODATA, so we
         * don't risk re-reading the same word
         */
        readl(trng->base + TRNG_ISR);
        ret = 4;

out:
        pm_runtime_put_sync_autosuspend(trng->dev);
        return ret;
}

static int atmel_trng_init(struct atmel_trng *trng)
{
        unsigned long rate;
        int ret;

        ret = clk_prepare_enable(trng->clk);
        if (ret)
                return ret;

        if (trng->has_half_rate) {
                rate = clk_get_rate(trng->clk);

                /* if peripheral clk is above 100MHz, set HALFR */
                if (rate > 100000000)
                        writel(TRNG_HALFR, trng->base + TRNG_MR);
        }

        writel(TRNG_KEY | 1, trng->base + TRNG_CR);

        return 0;
}

static void atmel_trng_cleanup(struct atmel_trng *trng)
{
        writel(TRNG_KEY, trng->base + TRNG_CR);
        clk_disable_unprepare(trng->clk);
}

static int atmel_trng_probe(struct platform_device *pdev)
{
        struct atmel_trng *trng;
        const struct atmel_trng_data *data;
        int ret;

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

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

        trng->clk = devm_clk_get(&pdev->dev, NULL);
        if (IS_ERR(trng->clk))
                return PTR_ERR(trng->clk);
        data = of_device_get_match_data(&pdev->dev);
        if (!data)
                return -ENODEV;

        trng->has_half_rate = data->has_half_rate;
        trng->dev = &pdev->dev;
        trng->rng.name = pdev->name;
        trng->rng.read = atmel_trng_read;
        platform_set_drvdata(pdev, trng);

#ifndef CONFIG_PM
        ret = atmel_trng_init(trng);
        if (ret)
                return ret;
#endif

        pm_runtime_set_autosuspend_delay(&pdev->dev, 100);
        pm_runtime_use_autosuspend(&pdev->dev);
        pm_runtime_enable(&pdev->dev);

        ret = devm_hwrng_register(&pdev->dev, &trng->rng);
        if (ret) {
                pm_runtime_disable(&pdev->dev);
                pm_runtime_set_suspended(&pdev->dev);
#ifndef CONFIG_PM
                atmel_trng_cleanup(trng);
#endif
        }

        return ret;
}

static void atmel_trng_remove(struct platform_device *pdev)
{
        struct atmel_trng *trng = platform_get_drvdata(pdev);

        atmel_trng_cleanup(trng);
        pm_runtime_disable(&pdev->dev);
        pm_runtime_set_suspended(&pdev->dev);
}

static int __maybe_unused atmel_trng_runtime_suspend(struct device *dev)
{
        struct atmel_trng *trng = dev_get_drvdata(dev);

        atmel_trng_cleanup(trng);

        return 0;
}

static int __maybe_unused atmel_trng_runtime_resume(struct device *dev)
{
        struct atmel_trng *trng = dev_get_drvdata(dev);

        return atmel_trng_init(trng);
}

static const struct dev_pm_ops __maybe_unused atmel_trng_pm_ops = {
        SET_RUNTIME_PM_OPS(atmel_trng_runtime_suspend,
                           atmel_trng_runtime_resume, NULL)
        SET_SYSTEM_SLEEP_PM_OPS(pm_runtime_force_suspend,
                                pm_runtime_force_resume)
};

static const struct atmel_trng_data at91sam9g45_config = {
        .has_half_rate = false,
};

static const struct atmel_trng_data sam9x60_config = {
        .has_half_rate = true,
};

static const struct of_device_id atmel_trng_dt_ids[] = {
        {
                .compatible = "atmel,at91sam9g45-trng",
                .data = &at91sam9g45_config,
        }, {
                .compatible = "microchip,sam9x60-trng",
                .data = &sam9x60_config,
        }, {
                /* sentinel */
        }
};
MODULE_DEVICE_TABLE(of, atmel_trng_dt_ids);

static struct platform_driver atmel_trng_driver = {
        .probe          = atmel_trng_probe,
        .remove         = atmel_trng_remove,
        .driver         = {
                .name   = "atmel-trng",
                .pm     = pm_ptr(&atmel_trng_pm_ops),
                .of_match_table = atmel_trng_dt_ids,
        },
};

module_platform_driver(atmel_trng_driver);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Peter Korsgaard <jacmet@sunsite.dk>");
MODULE_DESCRIPTION("Atmel true random number generator driver");