// SPDX-License-Identifier: GPL-2.0-only
/*
 * drivers/char/hw_random/timeriomem-rng.c
 *
 * Copyright (C) 2009 Alexander Clouter <alex@digriz.org.uk>
 *
 * Derived from drivers/char/hw_random/omap-rng.c
 *   Copyright 2005 (c) MontaVista Software, Inc.
 *   Author: Deepak Saxena <dsaxena@plexity.net>
 *
 * 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/completion.h>
#include <linux/delay.h>
#include <linux/hrtimer.h>
#include <linux/hw_random.h>
#include <linux/io.h>
#include <linux/ktime.h>
#include <linux/module.h>
#include <linux/of.h>
#include <linux/platform_device.h>
#include <linux/slab.h>
#include <linux/time.h>
#include <linux/timeriomem-rng.h>

struct timeriomem_rng_private {
        void __iomem            *io_base;
        ktime_t                 period;
        unsigned int            present:1;

        struct hrtimer          timer;
        struct completion       completion;

        struct hwrng            rng_ops;
};

static int timeriomem_rng_read(struct hwrng *hwrng, void *data,
                                size_t max, bool wait)
{
        struct timeriomem_rng_private *priv =
                container_of(hwrng, struct timeriomem_rng_private, rng_ops);
        int retval = 0;
        int period_us = ktime_to_us(priv->period);

        /*
         * There may not have been enough time for new data to be generated
         * since the last request.  If the caller doesn't want to wait, let them
         * bail out.  Otherwise, wait for the completion.  If the new data has
         * already been generated, the completion should already be available.
         */
        if (!wait && !priv->present)
                return 0;

        wait_for_completion(&priv->completion);

        do {
                /*
                 * After the first read, all additional reads will need to wait
                 * for the RNG to generate new data.  Since the period can have
                 * a wide range of values (1us to 1s have been observed), allow
                 * for 1% tolerance in the sleep time rather than a fixed value.
                 */
                if (retval > 0)
                        usleep_range(period_us,
                                        period_us + max(1, period_us / 100));

                *(u32 *)data = readl(priv->io_base);
                retval += sizeof(u32);
                data += sizeof(u32);
                max -= sizeof(u32);
        } while (wait && max > sizeof(u32));

        /*
         * Block any new callers until the RNG has had time to generate new
         * data.
         */
        priv->present = 0;
        reinit_completion(&priv->completion);
        hrtimer_forward_now(&priv->timer, priv->period);
        hrtimer_restart(&priv->timer);

        return retval;
}

static enum hrtimer_restart timeriomem_rng_trigger(struct hrtimer *timer)
{
        struct timeriomem_rng_private *priv
                = container_of(timer, struct timeriomem_rng_private, timer);

        priv->present = 1;
        complete(&priv->completion);

        return HRTIMER_NORESTART;
}

static int timeriomem_rng_probe(struct platform_device *pdev)
{
        struct timeriomem_rng_data *pdata = pdev->dev.platform_data;
        struct timeriomem_rng_private *priv;
        struct resource *res;
        int err = 0;
        int period;

        if (!pdev->dev.of_node && !pdata) {
                dev_err(&pdev->dev, "timeriomem_rng_data is missing\n");
                return -EINVAL;
        }

        /* Allocate memory for the device structure (and zero it) */
        priv = devm_kzalloc(&pdev->dev,
                        sizeof(struct timeriomem_rng_private), GFP_KERNEL);
        if (!priv)
                return -ENOMEM;

        platform_set_drvdata(pdev, priv);

        priv->io_base = devm_platform_get_and_ioremap_resource(pdev, 0, &res);
        if (IS_ERR(priv->io_base))
                return PTR_ERR(priv->io_base);

        if (res->start % 4 != 0 || resource_size(res) < 4) {
                dev_err(&pdev->dev,
                        "address must be at least four bytes wide and 32-bit aligned\n");
                return -EINVAL;
        }

        if (pdev->dev.of_node) {
                int i;

                if (!of_property_read_u32(pdev->dev.of_node,
                                                "period", &i))
                        period = i;
                else {
                        dev_err(&pdev->dev, "missing period\n");
                        return -EINVAL;
                }

                if (!of_property_read_u32(pdev->dev.of_node,
                                                "quality", &i))
                        priv->rng_ops.quality = i;
        } else {
                period = pdata->period;
                priv->rng_ops.quality = pdata->quality;
        }

        priv->period = us_to_ktime(period);
        init_completion(&priv->completion);
        hrtimer_setup(&priv->timer, timeriomem_rng_trigger, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);

        priv->rng_ops.name = dev_name(&pdev->dev);
        priv->rng_ops.read = timeriomem_rng_read;

        /* Assume random data is already available. */
        priv->present = 1;
        complete(&priv->completion);

        err = devm_hwrng_register(&pdev->dev, &priv->rng_ops);
        if (err) {
                dev_err(&pdev->dev, "problem registering\n");
                return err;
        }

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

        return 0;
}

static void timeriomem_rng_remove(struct platform_device *pdev)
{
        struct timeriomem_rng_private *priv = platform_get_drvdata(pdev);

        hrtimer_cancel(&priv->timer);
}

static const struct of_device_id timeriomem_rng_match[] = {
        { .compatible = "timeriomem_rng" },
        {},
};
MODULE_DEVICE_TABLE(of, timeriomem_rng_match);

static struct platform_driver timeriomem_rng_driver = {
        .driver = {
                .name           = "timeriomem_rng",
                .of_match_table = timeriomem_rng_match,
        },
        .probe          = timeriomem_rng_probe,
        .remove         = timeriomem_rng_remove,
};

module_platform_driver(timeriomem_rng_driver);

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Alexander Clouter <alex@digriz.org.uk>");
MODULE_DESCRIPTION("Timer IOMEM H/W RNG driver");