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

   1// SPDX-License-Identifier: GPL-2.0-or-later
   2/*
   3 * Nomadik RNG support
   4 *  Copyright 2009 Alessandro Rubini
   5 */
   6
   7#include <linux/kernel.h>
   8#include <linux/module.h>
   9#include <linux/device.h>
  10#include <linux/amba/bus.h>
  11#include <linux/hw_random.h>
  12#include <linux/io.h>
  13#include <linux/clk.h>
  14#include <linux/err.h>
  15
  16static struct clk *rng_clk;
  17
  18static int nmk_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
  19{
  20        void __iomem *base = (void __iomem *)rng->priv;
  21
  22        /*
  23         * The register is 32 bits and gives 16 random bits (low half).
  24         * A subsequent read will delay the core for 400ns, so we just read
  25         * once and accept the very unlikely very small delay, even if wait==0.
  26         */
  27        *(u16 *)data = __raw_readl(base + 8) & 0xffff;
  28        return 2;
  29}
  30
  31/* we have at most one RNG per machine, granted */
  32static struct hwrng nmk_rng = {
  33        .name           = "nomadik",
  34        .read           = nmk_rng_read,
  35};
  36
  37static int nmk_rng_probe(struct amba_device *dev, const struct amba_id *id)
  38{
  39        void __iomem *base;
  40        int ret;
  41
  42        rng_clk = devm_clk_get(&dev->dev, NULL);
  43        if (IS_ERR(rng_clk)) {
  44                dev_err(&dev->dev, "could not get rng clock\n");
  45                ret = PTR_ERR(rng_clk);
  46                return ret;
  47        }
  48
  49        clk_prepare_enable(rng_clk);
  50
  51        ret = amba_request_regions(dev, dev->dev.init_name);
  52        if (ret)
  53                goto out_clk;
  54        ret = -ENOMEM;
  55        base = devm_ioremap(&dev->dev, dev->res.start,
  56                            resource_size(&dev->res));
  57        if (!base)
  58                goto out_release;
  59        nmk_rng.priv = (unsigned long)base;
  60        ret = devm_hwrng_register(&dev->dev, &nmk_rng);
  61        if (ret)
  62                goto out_release;
  63        return 0;
  64
  65out_release:
  66        amba_release_regions(dev);
  67out_clk:
  68        clk_disable(rng_clk);
  69        return ret;
  70}
  71
  72static void nmk_rng_remove(struct amba_device *dev)
  73{
  74        amba_release_regions(dev);
  75        clk_disable(rng_clk);
  76}
  77
  78static const struct amba_id nmk_rng_ids[] = {
  79        {
  80                .id     = 0x000805e1,
  81                .mask   = 0x000fffff, /* top bits are rev and cfg: accept all */
  82        },
  83        {0, 0},
  84};
  85
  86MODULE_DEVICE_TABLE(amba, nmk_rng_ids);
  87
  88static struct amba_driver nmk_rng_driver = {
  89        .drv = {
  90                .owner = THIS_MODULE,
  91                .name = "rng",
  92                },
  93        .probe = nmk_rng_probe,
  94        .remove = nmk_rng_remove,
  95        .id_table = nmk_rng_ids,
  96};
  97
  98module_amba_driver(nmk_rng_driver);
  99
 100MODULE_LICENSE("GPL");
 101