timeriomem-rng.c

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/*
 * drivers/char/hw_random/timeriomem-rng.c
 *
 * Copyright (C) 2009 Alexander Clouter <[email protected]>
 *
 * Derived from drivers/char/hw_random/omap-rng.c
 *   Copyright 2005 (c) MontaVista Software, Inc.
 *   Author: Deepak Saxena <[email protected]>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 *
 * Overview:
 *   This driver is useful for platforms that have an IO range that provides
 *   periodic random data from a single IO memory address.  All the platform
 *   has to do is provide the address and 'wait time' that new data becomes
 *   available.
 *
 * TODO: add support for reading sizes other than 32bits and masking
 */

#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/platform_device.h>
#include <linux/hw_random.h>
#include <linux/io.h>
#include <linux/timeriomem-rng.h>
#include <linux/jiffies.h>
#include <linux/sched.h>
#include <linux/timer.h>
#include <linux/completion.h>

static struct timeriomem_rng_data *timeriomem_rng_data;

static void timeriomem_rng_trigger(unsigned long);
static DEFINE_TIMER(timeriomem_rng_timer, timeriomem_rng_trigger, 0, 0);

/*
 * have data return 1, however return 0 if we have nothing
 */
static int timeriomem_rng_data_present(struct hwrng *rng, int wait)
{
    if (rng->priv == 0)
        return 1;

    if (!wait || timeriomem_rng_data->present)
        return timeriomem_rng_data->present;

    wait_for_completion(&timeriomem_rng_data->completion);

    return 1;
}

static int timeriomem_rng_data_read(struct hwrng *rng, u32 *data)
{
    unsigned long cur;
    s32 delay;

    *data = readl(timeriomem_rng_data->address);

    if (rng->priv != 0) {
        cur = jiffies;

        delay = cur - timeriomem_rng_timer.expires;
        delay = rng->priv - (delay % rng->priv);

        timeriomem_rng_timer.expires = cur + delay;
        timeriomem_rng_data->present = 0;

        init_completion(&timeriomem_rng_data->completion);
        add_timer(&timeriomem_rng_timer);
    }

    return 4;
}

static void timeriomem_rng_trigger(unsigned long dummy)
{
    timeriomem_rng_data->present = 1;
    complete(&timeriomem_rng_data->completion);
}

static struct hwrng timeriomem_rng_ops = {
    .name       = "timeriomem",
    .data_present   = timeriomem_rng_data_present,
    .data_read  = timeriomem_rng_data_read,
    .priv       = 0,
};

static int __devinit timeriomem_rng_probe(struct platform_device *pdev)
{
    struct resource *res;
    int ret;

    res = platform_get_resource(pdev, IORESOURCE_MEM, 0);

    if (!res)
        return -ENOENT;

    timeriomem_rng_data = pdev->dev.platform_data;

    timeriomem_rng_data->address = ioremap(res->start, resource_size(res));
    if (!timeriomem_rng_data->address)
        return -EIO;

    if (timeriomem_rng_data->period != 0
        && usecs_to_jiffies(timeriomem_rng_data->period) > 0) {
        timeriomem_rng_timer.expires = jiffies;

        timeriomem_rng_ops.priv = usecs_to_jiffies(
                        timeriomem_rng_data->period);
    }
    timeriomem_rng_data->present = 1;

    ret = hwrng_register(&timeriomem_rng_ops);
    if (ret)
        goto failed;

    dev_info(&pdev->dev, "32bits from 0x%p @ %dus\n",
            timeriomem_rng_data->address,
            timeriomem_rng_data->period);

    return 0;

failed:
    dev_err(&pdev->dev, "problem registering\n");
    iounmap(timeriomem_rng_data->address);

    return ret;
}

static int __devexit timeriomem_rng_remove(struct platform_device *pdev)
{
    del_timer_sync(&timeriomem_rng_timer);
    hwrng_unregister(&timeriomem_rng_ops);

    iounmap(timeriomem_rng_data->address);

    return 0;
}

static struct platform_driver timeriomem_rng_driver = {
    .driver = {
        .name       = "timeriomem_rng",
        .owner      = THIS_MODULE,
    },
    .probe      = timeriomem_rng_probe,
    .remove     = __devexit_p(timeriomem_rng_remove),
};

module_platform_driver(timeriomem_rng_driver);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Alexander Clouter <[email protected]>");
MODULE_DESCRIPTION("Timer IOMEM H/W RNG driver");