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
  16 static struct clk *rng_clk;
  17
  18 static 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 */
  32 static struct hwrng nmk_rng = {
  33         .name           = "nomadik",
  34         .read           = nmk_rng_read,
  35 };
  36
  37 static 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
  65 out_release:
  66         amba_release_regions(dev);
  67 out_clk:
  68         clk_disable(rng_clk);
  69         return ret;
  70 }
  71
  72 static void nmk_rng_remove(struct amba_device *dev)
  73 {
  74         amba_release_regions(dev);
  75         clk_disable(rng_clk);
  76 }
  77
  78 static 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
  86 MODULE_DEVICE_TABLE(amba, nmk_rng_ids);
  87
  88 static 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
  98 module_amba_driver(nmk_rng_driver);
  99
 100 MODULE_LICENSE("GPL");