drivers/char/hw_random/st-rng.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 /*
   3  * ST Random Number Generator Driver ST's Platforms
   4  *
   5  * Author: Pankaj Dev: <pankaj.dev@st.com>
   6  *         Lee Jones <lee.jones@linaro.org>
   7  *
   8  * Copyright (C) 2015 STMicroelectronics (R&D) Limited
   9  */
  10
  11 #include <linux/clk.h>
  12 #include <linux/delay.h>
  13 #include <linux/hw_random.h>
  14 #include <linux/io.h>
  15 #include <linux/module.h>
  16 #include <linux/of.h>
  17 #include <linux/platform_device.h>
  18 #include <linux/slab.h>
  19
  20 /* Registers */
  21 #define ST_RNG_STATUS_REG               0x20
  22 #define ST_RNG_DATA_REG                 0x24
  23
  24 /* Registers fields */
  25 #define ST_RNG_STATUS_BAD_SEQUENCE      BIT(0)
  26 #define ST_RNG_STATUS_BAD_ALTERNANCE    BIT(1)
  27 #define ST_RNG_STATUS_FIFO_FULL         BIT(5)
  28
  29 #define ST_RNG_SAMPLE_SIZE              2 /* 2 Byte (16bit) samples */
  30 #define ST_RNG_FIFO_DEPTH               4
  31 #define ST_RNG_FIFO_SIZE                (ST_RNG_FIFO_DEPTH * ST_RNG_SAMPLE_SIZE)
  32
  33 /*
  34  * Samples are documented to be available every 0.667us, so in theory
  35  * the 4 sample deep FIFO should take 2.668us to fill.  However, during
  36  * thorough testing, it became apparent that filling the FIFO actually
  37  * takes closer to 12us.  We then multiply by 2 in order to account for
  38  * the lack of udelay()'s reliability, suggested by Russell King.
  39  */
  40 #define ST_RNG_FILL_FIFO_TIMEOUT        (12 * 2)
  41
  42 struct st_rng_data {
  43         void __iomem    *base;
  44         struct clk      *clk;
  45         struct hwrng    ops;
  46 };
  47
  48 static int st_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
  49 {
  50         struct st_rng_data *ddata = (struct st_rng_data *)rng->priv;
  51         u32 status;
  52         int i;
  53
  54         /* Wait until FIFO is full - max 4uS*/
  55         for (i = 0; i < ST_RNG_FILL_FIFO_TIMEOUT; i++) {
  56                 status = readl_relaxed(ddata->base + ST_RNG_STATUS_REG);
  57                 if (status & ST_RNG_STATUS_FIFO_FULL)
  58                         break;
  59                 udelay(1);
  60         }
  61
  62         if (i == ST_RNG_FILL_FIFO_TIMEOUT)
  63                 return 0;
  64
  65         for (i = 0; i < ST_RNG_FIFO_SIZE && i < max; i += 2)
  66                 *(u16 *)(data + i) =
  67                         readl_relaxed(ddata->base + ST_RNG_DATA_REG);
  68
  69         return i;       /* No of bytes read */
  70 }
  71
  72 static int st_rng_probe(struct platform_device *pdev)
  73 {
  74         struct st_rng_data *ddata;
  75         struct clk *clk;
  76         void __iomem *base;
  77         int ret;
  78
  79         ddata = devm_kzalloc(&pdev->dev, sizeof(*ddata), GFP_KERNEL);
  80         if (!ddata)
  81                 return -ENOMEM;
  82
  83         base = devm_platform_ioremap_resource(pdev, 0);
  84         if (IS_ERR(base))
  85                 return PTR_ERR(base);
  86
  87         clk = devm_clk_get(&pdev->dev, NULL);
  88         if (IS_ERR(clk))
  89                 return PTR_ERR(clk);
  90
  91         ret = clk_prepare_enable(clk);
  92         if (ret)
  93                 return ret;
  94
  95         ddata->ops.priv = (unsigned long)ddata;
  96         ddata->ops.read = st_rng_read;
  97         ddata->ops.name = pdev->name;
  98         ddata->base     = base;
  99         ddata->clk      = clk;
 100
 101         dev_set_drvdata(&pdev->dev, ddata);
 102
 103         ret = devm_hwrng_register(&pdev->dev, &ddata->ops);
 104         if (ret) {
 105                 dev_err(&pdev->dev, "Failed to register HW RNG\n");
 106                 clk_disable_unprepare(clk);
 107                 return ret;
 108         }
 109
 110         dev_info(&pdev->dev, "Successfully registered HW RNG\n");
 111
 112         return 0;
 113 }
 114
 115 static int st_rng_remove(struct platform_device *pdev)
 116 {
 117         struct st_rng_data *ddata = dev_get_drvdata(&pdev->dev);
 118
 119         clk_disable_unprepare(ddata->clk);
 120
 121         return 0;
 122 }
 123
 124 static const struct of_device_id st_rng_match[] = {
 125         { .compatible = "st,rng" },
 126         {},
 127 };
 128 MODULE_DEVICE_TABLE(of, st_rng_match);
 129
 130 static struct platform_driver st_rng_driver = {
 131         .driver = {
 132                 .name = "st-hwrandom",
 133                 .of_match_table = of_match_ptr(st_rng_match),
 134         },
 135         .probe = st_rng_probe,
 136         .remove = st_rng_remove
 137 };
 138
 139 module_platform_driver(st_rng_driver);
 140
 141 MODULE_AUTHOR("Pankaj Dev <pankaj.dev@st.com>");
 142 MODULE_LICENSE("GPL v2");