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

   1/*
   2 * Nomadik RNG support
   3 *  Copyright 2009 Alessandro Rubini
   4 *
   5 *  This program is free software; you can redistribute it and/or modify
   6 *  it under the terms of the GNU General Public License as published by
   7 *  the Free Software Foundation; either version 2 of the License, or
   8 *  (at your option) any later version.
   9 */
  10
  11#include <linux/kernel.h>
  12#include <linux/module.h>
  13#include <linux/init.h>
  14#include <linux/device.h>
  15#include <linux/amba/bus.h>
  16#include <linux/hw_random.h>
  17#include <linux/io.h>
  18#include <linux/clk.h>
  19#include <linux/err.h>
  20
  21static struct clk *rng_clk;
  22
  23static int nmk_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
  24{
  25        void __iomem *base = (void __iomem *)rng->priv;
  26
  27        /*
  28         * The register is 32 bits and gives 16 random bits (low half).
  29         * A subsequent read will delay the core for 400ns, so we just read
  30         * once and accept the very unlikely very small delay, even if wait==0.
  31         */
  32        *(u16 *)data = __raw_readl(base + 8) & 0xffff;
  33        return 2;
  34}
  35
  36/* we have at most one RNG per machine, granted */
  37static struct hwrng nmk_rng = {
  38        .name           = "nomadik",
  39        .read           = nmk_rng_read,
  40};
  41
  42static int nmk_rng_probe(struct amba_device *dev, const struct amba_id *id)
  43{
  44        void __iomem *base;
  45        int ret;
  46
  47        rng_clk = clk_get(&dev->dev, NULL);
  48        if (IS_ERR(rng_clk)) {
  49                dev_err(&dev->dev, "could not get rng clock\n");
  50                ret = PTR_ERR(rng_clk);
  51                return ret;
  52        }
  53
  54        clk_enable(rng_clk);
  55
  56        ret = amba_request_regions(dev, dev->dev.init_name);
  57        if (ret)
  58                goto out_clk;
  59        ret = -ENOMEM;
  60        base = ioremap(dev->res.start, resource_size(&dev->res));
  61        if (!base)
  62                goto out_release;
  63        nmk_rng.priv = (unsigned long)base;
  64        ret = hwrng_register(&nmk_rng);
  65        if (ret)
  66                goto out_unmap;
  67        return 0;
  68
  69out_unmap:
  70        iounmap(base);
  71out_release:
  72        amba_release_regions(dev);
  73out_clk:
  74        clk_disable(rng_clk);
  75        clk_put(rng_clk);
  76        return ret;
  77}
  78
  79static int nmk_rng_remove(struct amba_device *dev)
  80{
  81        void __iomem *base = (void __iomem *)nmk_rng.priv;
  82        hwrng_unregister(&nmk_rng);
  83        iounmap(base);
  84        amba_release_regions(dev);
  85        clk_disable(rng_clk);
  86        clk_put(rng_clk);
  87        return 0;
  88}
  89
  90static struct amba_id nmk_rng_ids[] = {
  91        {
  92                .id     = 0x000805e1,
  93                .mask   = 0x000fffff, /* top bits are rev and cfg: accept all */
  94        },
  95        {0, 0},
  96};
  97
  98MODULE_DEVICE_TABLE(amba, nmk_rng_ids);
  99
 100static struct amba_driver nmk_rng_driver = {
 101        .drv = {
 102                .owner = THIS_MODULE,
 103                .name = "rng",
 104                },
 105        .probe = nmk_rng_probe,
 106        .remove = nmk_rng_remove,
 107        .id_table = nmk_rng_ids,
 108};
 109
 110module_amba_driver(nmk_rng_driver);
 111
 112MODULE_LICENSE("GPL");
 113