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/hw_random.h>
  27 #include <linux/io.h>
  28 #include <linux/timeriomem-rng.h>
  29 #include <linux/jiffies.h>
  30 #include <linux/sched.h>
  31 #include <linux/timer.h>
  32 #include <linux/completion.h>
  33
  34 static struct timeriomem_rng_data *timeriomem_rng_data;
  35
  36 static void timeriomem_rng_trigger(unsigned long);
  37 static DEFINE_TIMER(timeriomem_rng_timer, timeriomem_rng_trigger, 0, 0);
  38
  39 /*
  40  * have data return 1, however return 0 if we have nothing
  41  */
  42 static int timeriomem_rng_data_present(struct hwrng *rng, int wait)
  43 {
  44         if (rng->priv == 0)
  45                 return 1;
  46
  47         if (!wait || timeriomem_rng_data->present)
  48                 return timeriomem_rng_data->present;
  49
  50         wait_for_completion(&timeriomem_rng_data->completion);
  51
  52         return 1;
  53 }
  54
  55 static int timeriomem_rng_data_read(struct hwrng *rng, u32 *data)
  56 {
  57         unsigned long cur;
  58         s32 delay;
  59
  60         *data = readl(timeriomem_rng_data->address);
  61
  62         if (rng->priv != 0) {
  63                 cur = jiffies;
  64
  65                 delay = cur - timeriomem_rng_timer.expires;
  66                 delay = rng->priv - (delay % rng->priv);
  67
  68                 timeriomem_rng_timer.expires = cur + delay;
  69                 timeriomem_rng_data->present = 0;
  70
  71                 init_completion(&timeriomem_rng_data->completion);
  72                 add_timer(&timeriomem_rng_timer);
  73         }
  74
  75         return 4;
  76 }
  77
  78 static void timeriomem_rng_trigger(unsigned long dummy)
  79 {
  80         timeriomem_rng_data->present = 1;
  81         complete(&timeriomem_rng_data->completion);
  82 }
  83
  84 static struct hwrng timeriomem_rng_ops = {
  85         .name           = "timeriomem",
  86         .data_present   = timeriomem_rng_data_present,
  87         .data_read      = timeriomem_rng_data_read,
  88         .priv           = 0,
  89 };
  90
  91 static int timeriomem_rng_probe(struct platform_device *pdev)
  92 {
  93         struct resource *res;
  94         int ret;
  95
  96         res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
  97
  98         if (!res)
  99                 return -ENOENT;
 100
 101         timeriomem_rng_data = pdev->dev.platform_data;
 102
 103         timeriomem_rng_data->address = ioremap(res->start, resource_size(res));
 104         if (!timeriomem_rng_data->address)
 105                 return -EIO;
 106
 107         if (timeriomem_rng_data->period != 0
 108                 && usecs_to_jiffies(timeriomem_rng_data->period) > 0) {
 109                 timeriomem_rng_timer.expires = jiffies;
 110
 111                 timeriomem_rng_ops.priv = usecs_to_jiffies(
 112                                                 timeriomem_rng_data->period);
 113         }
 114         timeriomem_rng_data->present = 1;
 115
 116         ret = hwrng_register(&timeriomem_rng_ops);
 117         if (ret)
 118                 goto failed;
 119
 120         dev_info(&pdev->dev, "32bits from 0x%p @ %dus\n",
 121                         timeriomem_rng_data->address,
 122                         timeriomem_rng_data->period);
 123
 124         return 0;
 125
 126 failed:
 127         dev_err(&pdev->dev, "problem registering\n");
 128         iounmap(timeriomem_rng_data->address);
 129
 130         return ret;
 131 }
 132
 133 static int timeriomem_rng_remove(struct platform_device *pdev)
 134 {
 135         del_timer_sync(&timeriomem_rng_timer);
 136         hwrng_unregister(&timeriomem_rng_ops);
 137
 138         iounmap(timeriomem_rng_data->address);
 139
 140         return 0;
 141 }
 142
 143 static struct platform_driver timeriomem_rng_driver = {
 144         .driver = {
 145                 .name           = "timeriomem_rng",
 146                 .owner          = THIS_MODULE,
 147         },
 148         .probe          = timeriomem_rng_probe,
 149         .remove         = timeriomem_rng_remove,
 150 };
 151
 152 module_platform_driver(timeriomem_rng_driver);
 153
 154 MODULE_LICENSE("GPL");
 155 MODULE_AUTHOR("Alexander Clouter <alex@digriz.org.uk>");
 156 MODULE_DESCRIPTION("Timer IOMEM H/W RNG driver");