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/module.h>
  24 #include <linux/kernel.h>
  25 #include <linux/platform_device.h>
  26 #include <linux/of.h>
  27 #include <linux/hw_random.h>
  28 #include <linux/io.h>
  29 #include <linux/slab.h>
  30 #include <linux/timeriomem-rng.h>
  31 #include <linux/jiffies.h>
  32 #include <linux/sched.h>
  33 #include <linux/timer.h>
  34 #include <linux/completion.h>
  35
  36 struct timeriomem_rng_private_data {
  37         void __iomem            *io_base;
  38         unsigned int            expires;
  39         unsigned int            period;
  40         unsigned int            present:1;
  41
  42         struct timer_list       timer;
  43         struct completion       completion;
  44
  45         struct hwrng            timeriomem_rng_ops;
  46 };
  47
  48 #define to_rng_priv(rng) \
  49                 ((struct timeriomem_rng_private_data *)rng->priv)
  50
  51 /*
  52  * have data return 1, however return 0 if we have nothing
  53  */
  54 static int timeriomem_rng_data_present(struct hwrng *rng, int wait)
  55 {
  56         struct timeriomem_rng_private_data *priv = to_rng_priv(rng);
  57
  58         if (!wait || priv->present)
  59                 return priv->present;
  60
  61         wait_for_completion(&priv->completion);
  62
  63         return 1;
  64 }
  65
  66 static int timeriomem_rng_data_read(struct hwrng *rng, u32 *data)
  67 {
  68         struct timeriomem_rng_private_data *priv = to_rng_priv(rng);
  69         unsigned long cur;
  70         s32 delay;
  71
  72         *data = readl(priv->io_base);
  73
  74         cur = jiffies;
  75
  76         delay = cur - priv->expires;
  77         delay = priv->period - (delay % priv->period);
  78
  79         priv->expires = cur + delay;
  80         priv->present = 0;
  81
  82         reinit_completion(&priv->completion);
  83         mod_timer(&priv->timer, priv->expires);
  84
  85         return 4;
  86 }
  87
  88 static void timeriomem_rng_trigger(unsigned long data)
  89 {
  90         struct timeriomem_rng_private_data *priv
  91                         = (struct timeriomem_rng_private_data *)data;
  92
  93         priv->present = 1;
  94         complete(&priv->completion);
  95 }
  96
  97 static int timeriomem_rng_probe(struct platform_device *pdev)
  98 {
  99         struct timeriomem_rng_data *pdata = pdev->dev.platform_data;
 100         struct timeriomem_rng_private_data *priv;
 101         struct resource *res;
 102         int err = 0;
 103         int period;
 104
 105         if (!pdev->dev.of_node && !pdata) {
 106                 dev_err(&pdev->dev, "timeriomem_rng_data is missing\n");
 107                 return -EINVAL;
 108         }
 109
 110         res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
 111         if (!res)
 112                 return -ENXIO;
 113
 114         if (res->start % 4 != 0 || resource_size(res) != 4) {
 115                 dev_err(&pdev->dev,
 116                         "address must be four bytes wide and aligned\n");
 117                 return -EINVAL;
 118         }
 119
 120         /* Allocate memory for the device structure (and zero it) */
 121         priv = devm_kzalloc(&pdev->dev,
 122                         sizeof(struct timeriomem_rng_private_data), GFP_KERNEL);
 123         if (!priv)
 124                 return -ENOMEM;
 125
 126         platform_set_drvdata(pdev, priv);
 127
 128         if (pdev->dev.of_node) {
 129                 int i;
 130
 131                 if (!of_property_read_u32(pdev->dev.of_node,
 132                                                 "period", &i))
 133                         period = i;
 134                 else {
 135                         dev_err(&pdev->dev, "missing period\n");
 136                         return -EINVAL;
 137                 }
 138         } else {
 139                 period = pdata->period;
 140         }
 141
 142         priv->period = usecs_to_jiffies(period);
 143         if (priv->period < 1) {
 144                 dev_err(&pdev->dev, "period is less than one jiffy\n");
 145                 return -EINVAL;
 146         }
 147
 148         priv->expires   = jiffies;
 149         priv->present   = 1;
 150
 151         init_completion(&priv->completion);
 152         complete(&priv->completion);
 153
 154         setup_timer(&priv->timer, timeriomem_rng_trigger, (unsigned long)priv);
 155
 156         priv->timeriomem_rng_ops.name           = dev_name(&pdev->dev);
 157         priv->timeriomem_rng_ops.data_present   = timeriomem_rng_data_present;
 158         priv->timeriomem_rng_ops.data_read      = timeriomem_rng_data_read;
 159         priv->timeriomem_rng_ops.priv           = (unsigned long)priv;
 160
 161         priv->io_base = devm_ioremap_resource(&pdev->dev, res);
 162         if (IS_ERR(priv->io_base)) {
 163                 err = PTR_ERR(priv->io_base);
 164                 goto out_timer;
 165         }
 166
 167         err = hwrng_register(&priv->timeriomem_rng_ops);
 168         if (err) {
 169                 dev_err(&pdev->dev, "problem registering\n");
 170                 goto out_timer;
 171         }
 172
 173         dev_info(&pdev->dev, "32bits from 0x%p @ %dus\n",
 174                         priv->io_base, period);
 175
 176         return 0;
 177
 178 out_timer:
 179         del_timer_sync(&priv->timer);
 180         return err;
 181 }
 182
 183 static int timeriomem_rng_remove(struct platform_device *pdev)
 184 {
 185         struct timeriomem_rng_private_data *priv = platform_get_drvdata(pdev);
 186
 187         hwrng_unregister(&priv->timeriomem_rng_ops);
 188
 189         del_timer_sync(&priv->timer);
 190
 191         return 0;
 192 }
 193
 194 static const struct of_device_id timeriomem_rng_match[] = {
 195         { .compatible = "timeriomem_rng" },
 196         {},
 197 };
 198 MODULE_DEVICE_TABLE(of, timeriomem_rng_match);
 199
 200 static struct platform_driver timeriomem_rng_driver = {
 201         .driver = {
 202                 .name           = "timeriomem_rng",
 203                 .of_match_table = timeriomem_rng_match,
 204         },
 205         .probe          = timeriomem_rng_probe,
 206         .remove         = timeriomem_rng_remove,
 207 };
 208
 209 module_platform_driver(timeriomem_rng_driver);
 210
 211 MODULE_LICENSE("GPL");
 212 MODULE_AUTHOR("Alexander Clouter <alex@digriz.org.uk>");
 213 MODULE_DESCRIPTION("Timer IOMEM H/W RNG driver");