/*
 * RNG driver for TX4939 Random Number Generators (RNG)
 *
 * Copyright (C) 2009 Atsushi Nemoto <anemo@mba.ocn.ne.jp>
 *
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file "COPYING" in the main directory of this archive
 * for more details.
 */
#include <linux/err.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/delay.h>
#include <linux/io.h>
#include <linux/platform_device.h>
#include <linux/hw_random.h>
#include <linux/gfp.h>

#define TX4939_RNG_RCSR         0x00000000
#define TX4939_RNG_ROR(n)       (0x00000018 + (n) * 8)

#define TX4939_RNG_RCSR_INTE    0x00000008
#define TX4939_RNG_RCSR_RST     0x00000004
#define TX4939_RNG_RCSR_FIN     0x00000002
#define TX4939_RNG_RCSR_ST      0x00000001

struct tx4939_rng {
        struct hwrng rng;
        void __iomem *base;
        u64 databuf[3];
        unsigned int data_avail;
};

static void rng_io_start(void)
{
#ifndef CONFIG_64BIT
        /*
         * readq is reading a 64-bit register using a 64-bit load.  On
         * a 32-bit kernel however interrupts or any other processor
         * exception would clobber the upper 32-bit of the processor
         * register so interrupts need to be disabled.
         */
        local_irq_disable();
#endif
}

static void rng_io_end(void)
{
#ifndef CONFIG_64BIT
        local_irq_enable();
#endif
}

static u64 read_rng(void __iomem *base, unsigned int offset)
{
        return ____raw_readq(base + offset);
}

static void write_rng(u64 val, void __iomem *base, unsigned int offset)
{
        return ____raw_writeq(val, base + offset);
}

static int tx4939_rng_data_present(struct hwrng *rng, int wait)
{
        struct tx4939_rng *rngdev = container_of(rng, struct tx4939_rng, rng);
        int i;

        if (rngdev->data_avail)
                return rngdev->data_avail;
        for (i = 0; i < 20; i++) {
                rng_io_start();
                if (!(read_rng(rngdev->base, TX4939_RNG_RCSR)
                      & TX4939_RNG_RCSR_ST)) {
                        rngdev->databuf[0] =
                                read_rng(rngdev->base, TX4939_RNG_ROR(0));
                        rngdev->databuf[1] =
                                read_rng(rngdev->base, TX4939_RNG_ROR(1));
                        rngdev->databuf[2] =
                                read_rng(rngdev->base, TX4939_RNG_ROR(2));
                        rngdev->data_avail =
                                sizeof(rngdev->databuf) / sizeof(u32);
                        /* Start RNG */
                        write_rng(TX4939_RNG_RCSR_ST,
                                  rngdev->base, TX4939_RNG_RCSR);
                        wait = 0;
                }
                rng_io_end();
                if (!wait)
                        break;
                /* 90 bus clock cycles by default for generation */
                ndelay(90 * 5);
        }
        return rngdev->data_avail;
}

static int tx4939_rng_data_read(struct hwrng *rng, u32 *buffer)
{
        struct tx4939_rng *rngdev = container_of(rng, struct tx4939_rng, rng);

        rngdev->data_avail--;
        *buffer = *((u32 *)&rngdev->databuf + rngdev->data_avail);
        return sizeof(u32);
}

static int __init tx4939_rng_probe(struct platform_device *dev)
{
        struct tx4939_rng *rngdev;
        struct resource *r;
        int i;

        r = platform_get_resource(dev, IORESOURCE_MEM, 0);
        if (!r)
                return -EBUSY;
        rngdev = devm_kzalloc(&dev->dev, sizeof(*rngdev), GFP_KERNEL);
        if (!rngdev)
                return -ENOMEM;
        rngdev->base = devm_ioremap_resource(&dev->dev, r);
        if (IS_ERR(rngdev->base))
                return PTR_ERR(rngdev->base);

        rngdev->rng.name = dev_name(&dev->dev);
        rngdev->rng.data_present = tx4939_rng_data_present;
        rngdev->rng.data_read = tx4939_rng_data_read;

        rng_io_start();
        /* Reset RNG */
        write_rng(TX4939_RNG_RCSR_RST, rngdev->base, TX4939_RNG_RCSR);
        write_rng(0, rngdev->base, TX4939_RNG_RCSR);
        /* Start RNG */
        write_rng(TX4939_RNG_RCSR_ST, rngdev->base, TX4939_RNG_RCSR);
        rng_io_end();
        /*
         * Drop first two results.  From the datasheet:
         * The quality of the random numbers generated immediately
         * after reset can be insufficient.  Therefore, do not use
         * random numbers obtained from the first and second
         * generations; use the ones from the third or subsequent
         * generation.
         */
        for (i = 0; i < 2; i++) {
                rngdev->data_avail = 0;
                if (!tx4939_rng_data_present(&rngdev->rng, 1))
                        return -EIO;
        }

        platform_set_drvdata(dev, rngdev);
        return hwrng_register(&rngdev->rng);
}

static int __exit tx4939_rng_remove(struct platform_device *dev)
{
        struct tx4939_rng *rngdev = platform_get_drvdata(dev);

        hwrng_unregister(&rngdev->rng);
        platform_set_drvdata(dev, NULL);
        return 0;
}

static struct platform_driver tx4939_rng_driver = {
        .driver         = {
                .name   = "tx4939-rng",
                .owner  = THIS_MODULE,
        },
        .remove = tx4939_rng_remove,
};

static int __init tx4939rng_init(void)
{
        return platform_driver_probe(&tx4939_rng_driver, tx4939_rng_probe);
}

static void __exit tx4939rng_exit(void)
{
        platform_driver_unregister(&tx4939_rng_driver);
}

module_init(tx4939rng_init);
module_exit(tx4939rng_exit);

MODULE_DESCRIPTION("H/W Random Number Generator (RNG) driver for TX4939");
MODULE_LICENSE("GPL");