drivers/char/hw_random/timeriomem-rng.c

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