tx4939-rng.c

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/*
 * RNG driver for TX4939 Random Number Generators (RNG)
 *
 * Copyright (C) 2009 Atsushi Nemoto <[email protected]>
 *
 * 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/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_request_and_ioremap(&dev->dev, r);
    if (!rngdev->base)
        return -EBUSY;

    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");