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/device.h>
  14#include <linux/amba/bus.h>
  15#include <linux/hw_random.h>
  16#include <linux/io.h>
  17#include <linux/clk.h>
  18#include <linux/err.h>
  19
  20static struct clk *rng_clk;
  21
  22static int nmk_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
  23{
  24        void __iomem *base = (void __iomem *)rng->priv;
  25
  26        /*
  27         * The register is 32 bits and gives 16 random bits (low half).
  28         * A subsequent read will delay the core for 400ns, so we just read
  29         * once and accept the very unlikely very small delay, even if wait==0.
  30         */
  31        *(u16 *)data = __raw_readl(base + 8) & 0xffff;
  32        return 2;
  33}
  34
  35/* we have at most one RNG per machine, granted */
  36static struct hwrng nmk_rng = {
  37        .name           = "nomadik",
  38        .read           = nmk_rng_read,
  39};
  40
  41static int nmk_rng_probe(struct amba_device *dev, const struct amba_id *id)
  42{
  43        void __iomem *base;
  44        int ret;
  45
  46        rng_clk = devm_clk_get(&dev->dev, NULL);
  47        if (IS_ERR(rng_clk)) {
  48                dev_err(&dev->dev, "could not get rng clock\n");
  49                ret = PTR_ERR(rng_clk);
  50                return ret;
  51        }
  52
  53        clk_prepare_enable(rng_clk);
  54
  55        ret = amba_request_regions(dev, dev->dev.init_name);
  56        if (ret)
  57                goto out_clk;
  58        ret = -ENOMEM;
  59        base = devm_ioremap(&dev->dev, dev->res.start,
  60                            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_release;
  67        return 0;
  68
  69out_release:
  70        amba_release_regions(dev);
  71out_clk:
  72        clk_disable(rng_clk);
  73        return ret;
  74}
  75
  76static int nmk_rng_remove(struct amba_device *dev)
  77{
  78        hwrng_unregister(&nmk_rng);
  79        amba_release_regions(dev);
  80        clk_disable(rng_clk);
  81        return 0;
  82}
  83
  84static struct amba_id nmk_rng_ids[] = {
  85        {
  86                .id     = 0x000805e1,
  87                .mask   = 0x000fffff, /* top bits are rev and cfg: accept all */
  88        },
  89        {0, 0},
  90};
  91
  92MODULE_DEVICE_TABLE(amba, nmk_rng_ids);
  93
  94static struct amba_driver nmk_rng_driver = {
  95        .drv = {
  96                .owner = THIS_MODULE,
  97                .name = "rng",
  98                },
  99        .probe = nmk_rng_probe,
 100        .remove = nmk_rng_remove,
 101        .id_table = nmk_rng_ids,
 102};
 103
 104module_amba_driver(nmk_rng_driver);
 105
 106MODULE_LICENSE("GPL");
 107