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