LXR linux/drivers/char/hw_random/timeriomem-rng.c

   1// SPDX-License-Identifier: GPL-2.0-only
   2/*
   3 * drivers/char/hw_random/timeriomem-rng.c
   4 *
   5 * Copyright (C) 2009 Alexander Clouter <alex@digriz.org.uk>
   6 *
   7 * Derived from drivers/char/hw_random/omap-rng.c
   8 *   Copyright 2005 (c) MontaVista Software, Inc.
   9 *   Author: Deepak Saxena <dsaxena@plexity.net>
  10 *
  11 * Overview:
  12 *   This driver is useful for platforms that have an IO range that provides
  13 *   periodic random data from a single IO memory address.  All the platform
  14 *   has to do is provide the address and 'wait time' that new data becomes
  15 *   available.
  16 *
  17 * TODO: add support for reading sizes other than 32bits and masking
  18 */
  19
  20#include <linux/completion.h>
  21#include <linux/delay.h>
  22#include <linux/hrtimer.h>
  23#include <linux/hw_random.h>
  24#include <linux/io.h>
  25#include <linux/ktime.h>
  26#include <linux/module.h>
  27#include <linux/of.h>
  28#include <linux/platform_device.h>
  29#include <linux/slab.h>
  30#include <linux/time.h>
  31#include <linux/timeriomem-rng.h>
  32
  33struct timeriomem_rng_private {
  34        void __iomem            *io_base;
  35        ktime_t                 period;
  36        unsigned int            present:1;
  37
  38        struct hrtimer          timer;
  39        struct completion       completion;
  40
  41        struct hwrng            rng_ops;
  42};
  43
  44static int timeriomem_rng_read(struct hwrng *hwrng, void *data,
  45                                size_t max, bool wait)
  46{
  47        struct timeriomem_rng_private *priv =
  48                container_of(hwrng, struct timeriomem_rng_private, rng_ops);
  49        int retval = 0;
  50        int period_us = ktime_to_us(priv->period);
  51
  52        /*
  53         * There may not have been enough time for new data to be generated
  54         * since the last request.  If the caller doesn't want to wait, let them
  55         * bail out.  Otherwise, wait for the completion.  If the new data has
  56         * already been generated, the completion should already be available.
  57         */
  58        if (!wait && !priv->present)
  59                return 0;
  60
  61        wait_for_completion(&priv->completion);
  62
  63        do {
  64                /*
  65                 * After the first read, all additional reads will need to wait
  66                 * for the RNG to generate new data.  Since the period can have
  67                 * a wide range of values (1us to 1s have been observed), allow
  68                 * for 1% tolerance in the sleep time rather than a fixed value.
  69                 */
  70                if (retval > 0)
  71                        usleep_range(period_us,
  72                                        period_us + max(1, period_us / 100));
  73
  74                *(u32 *)data = readl(priv->io_base);
  75                retval += sizeof(u32);
  76                data += sizeof(u32);
  77                max -= sizeof(u32);
  78        } while (wait && max > sizeof(u32));
  79
  80        /*
  81         * Block any new callers until the RNG has had time to generate new
  82         * data.
  83         */
  84        priv->present = 0;
  85        reinit_completion(&priv->completion);
  86        hrtimer_forward_now(&priv->timer, priv->period);
  87        hrtimer_restart(&priv->timer);
  88
  89        return retval;
  90}
  91
  92static enum hrtimer_restart timeriomem_rng_trigger(struct hrtimer *timer)
  93{
  94        struct timeriomem_rng_private *priv
  95                = container_of(timer, struct timeriomem_rng_private, timer);
  96
  97        priv->present = 1;
  98        complete(&priv->completion);
  99
 100        return HRTIMER_NORESTART;
 101}
 102
 103static int timeriomem_rng_probe(struct platform_device *pdev)
 104{
 105        struct timeriomem_rng_data *pdata = pdev->dev.platform_data;
 106        struct timeriomem_rng_private *priv;
 107        struct resource *res;
 108        int err = 0;
 109        int period;
 110
 111        if (!pdev->dev.of_node && !pdata) {
 112                dev_err(&pdev->dev, "timeriomem_rng_data is missing\n");
 113                return -EINVAL;
 114        }
 115
 116        res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
 117        if (!res)
 118                return -ENXIO;
 119
 120        if (res->start % 4 != 0 || resource_size(res) < 4) {
 121                dev_err(&pdev->dev,
 122                        "address must be at least four bytes wide and 32-bit aligned\n");
 123                return -EINVAL;
 124        }
 125
 126        /* Allocate memory for the device structure (and zero it) */
 127        priv = devm_kzalloc(&pdev->dev,
 128                        sizeof(struct timeriomem_rng_private), GFP_KERNEL);
 129        if (!priv)
 130                return -ENOMEM;
 131
 132        platform_set_drvdata(pdev, priv);
 133
 134        if (pdev->dev.of_node) {
 135                int i;
 136
 137                if (!of_property_read_u32(pdev->dev.of_node,
 138                                                "period", &i))
 139                        period = i;
 140                else {
 141                        dev_err(&pdev->dev, "missing period\n");
 142                        return -EINVAL;
 143                }
 144
 145                if (!of_property_read_u32(pdev->dev.of_node,
 146                                                "quality", &i))
 147                        priv->rng_ops.quality = i;
 148                else
 149                        priv->rng_ops.quality = 0;
 150        } else {
 151                period = pdata->period;
 152                priv->rng_ops.quality = pdata->quality;
 153        }
 154
 155        priv->period = ns_to_ktime(period * NSEC_PER_USEC);
 156        init_completion(&priv->completion);
 157        hrtimer_init(&priv->timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
 158        priv->timer.function = timeriomem_rng_trigger;
 159
 160        priv->rng_ops.name = dev_name(&pdev->dev);
 161        priv->rng_ops.read = timeriomem_rng_read;
 162
 163        priv->io_base = devm_ioremap_resource(&pdev->dev, res);
 164        if (IS_ERR(priv->io_base)) {
 165                return PTR_ERR(priv->io_base);
 166        }
 167
 168        /* Assume random data is already available. */
 169        priv->present = 1;
 170        complete(&priv->completion);
 171
 172        err = devm_hwrng_register(&pdev->dev, &priv->rng_ops);
 173        if (err) {
 174                dev_err(&pdev->dev, "problem registering\n");
 175                return err;
 176        }
 177
 178        dev_info(&pdev->dev, "32bits from 0x%p @ %dus\n",
 179                        priv->io_base, period);
 180
 181        return 0;
 182}
 183
 184static int timeriomem_rng_remove(struct platform_device *pdev)
 185{
 186        struct timeriomem_rng_private *priv = platform_get_drvdata(pdev);
 187
 188        hrtimer_cancel(&priv->timer);
 189
 190        return 0;
 191}
 192
 193static const struct of_device_id timeriomem_rng_match[] = {
 194        { .compatible = "timeriomem_rng" },
 195        {},
 196};
 197MODULE_DEVICE_TABLE(of, timeriomem_rng_match);
 198
 199static struct platform_driver timeriomem_rng_driver = {
 200        .driver = {
 201                .name           = "timeriomem_rng",
 202                .of_match_table = timeriomem_rng_match,
 203        },
 204        .probe          = timeriomem_rng_probe,
 205        .remove         = timeriomem_rng_remove,
 206};
 207
 208module_platform_driver(timeriomem_rng_driver);
 209
 210MODULE_LICENSE("GPL");
 211MODULE_AUTHOR("Alexander Clouter <alex@digriz.org.uk>");
 212MODULE_DESCRIPTION("Timer IOMEM H/W RNG driver");
 213