drivers/char/hw_random/st-rng.c

   1 /*
   2  * ST Random Number Generator Driver ST's Platforms
   3  *
   4  * Author: Pankaj Dev: <pankaj.dev@st.com>
   5  *         Lee Jones <lee.jones@linaro.org>
   6  *
   7  * Copyright (C) 2015 STMicroelectronics (R&D) Limited
   8  *
   9  * This program is free software; you can redistribute it and/or modify
  10  * it under the terms of the GNU General Public License version 2 as
  11  * published by the Free Software Foundation.
  12  */
  13
  14 #include <linux/clk.h>
  15 #include <linux/delay.h>
  16 #include <linux/hw_random.h>
  17 #include <linux/io.h>
  18 #include <linux/module.h>
  19 #include <linux/of.h>
  20 #include <linux/platform_device.h>
  21 #include <linux/slab.h>
  22
  23 /* Registers */
  24 #define ST_RNG_STATUS_REG               0x20
  25 #define ST_RNG_DATA_REG                 0x24
  26
  27 /* Registers fields */
  28 #define ST_RNG_STATUS_BAD_SEQUENCE      BIT(0)
  29 #define ST_RNG_STATUS_BAD_ALTERNANCE    BIT(1)
  30 #define ST_RNG_STATUS_FIFO_FULL         BIT(5)
  31
  32 #define ST_RNG_SAMPLE_SIZE              2 /* 2 Byte (16bit) samples */
  33 #define ST_RNG_FIFO_DEPTH               4
  34 #define ST_RNG_FIFO_SIZE                (ST_RNG_FIFO_DEPTH * ST_RNG_SAMPLE_SIZE)
  35
  36 /*
  37  * Samples are documented to be available every 0.667us, so in theory
  38  * the 4 sample deep FIFO should take 2.668us to fill.  However, during
  39  * thorough testing, it became apparent that filling the FIFO actually
  40  * takes closer to 12us.  We then multiply by 2 in order to account for
  41  * the lack of udelay()'s reliability, suggested by Russell King.
  42  */
  43 #define ST_RNG_FILL_FIFO_TIMEOUT        (12 * 2)
  44
  45 struct st_rng_data {
  46         void __iomem    *base;
  47         struct clk      *clk;
  48         struct hwrng    ops;
  49 };
  50
  51 static int st_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
  52 {
  53         struct st_rng_data *ddata = (struct st_rng_data *)rng->priv;
  54         u32 status;
  55         int i;
  56
  57         /* Wait until FIFO is full - max 4uS*/
  58         for (i = 0; i < ST_RNG_FILL_FIFO_TIMEOUT; i++) {
  59                 status = readl_relaxed(ddata->base + ST_RNG_STATUS_REG);
  60                 if (status & ST_RNG_STATUS_FIFO_FULL)
  61                         break;
  62                 udelay(1);
  63         }
  64
  65         if (i == ST_RNG_FILL_FIFO_TIMEOUT)
  66                 return 0;
  67
  68         for (i = 0; i < ST_RNG_FIFO_SIZE && i < max; i += 2)
  69                 *(u16 *)(data + i) =
  70                         readl_relaxed(ddata->base + ST_RNG_DATA_REG);
  71
  72         return i;       /* No of bytes read */
  73 }
  74
  75 static int st_rng_probe(struct platform_device *pdev)
  76 {
  77         struct st_rng_data *ddata;
  78         struct resource *res;
  79         struct clk *clk;
  80         void __iomem *base;
  81         int ret;
  82
  83         ddata = devm_kzalloc(&pdev->dev, sizeof(*ddata), GFP_KERNEL);
  84         if (!ddata)
  85                 return -ENOMEM;
  86
  87         res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
  88         base = devm_ioremap_resource(&pdev->dev, res);
  89         if (IS_ERR(base))
  90                 return PTR_ERR(base);
  91
  92         clk = devm_clk_get(&pdev->dev, NULL);
  93         if (IS_ERR(clk))
  94                 return PTR_ERR(clk);
  95
  96         ret = clk_prepare_enable(clk);
  97         if (ret)
  98                 return ret;
  99
 100         ddata->ops.priv = (unsigned long)ddata;
 101         ddata->ops.read = st_rng_read;
 102         ddata->ops.name = pdev->name;
 103         ddata->base     = base;
 104         ddata->clk      = clk;
 105
 106         dev_set_drvdata(&pdev->dev, ddata);
 107
 108         ret = hwrng_register(&ddata->ops);
 109         if (ret) {
 110                 dev_err(&pdev->dev, "Failed to register HW RNG\n");
 111                 clk_disable_unprepare(clk);
 112                 return ret;
 113         }
 114
 115         dev_info(&pdev->dev, "Successfully registered HW RNG\n");
 116
 117         return 0;
 118 }
 119
 120 static int st_rng_remove(struct platform_device *pdev)
 121 {
 122         struct st_rng_data *ddata = dev_get_drvdata(&pdev->dev);
 123
 124         hwrng_unregister(&ddata->ops);
 125
 126         clk_disable_unprepare(ddata->clk);
 127
 128         return 0;
 129 }
 130
 131 static const struct of_device_id st_rng_match[] = {
 132         { .compatible = "st,rng" },
 133         {},
 134 };
 135 MODULE_DEVICE_TABLE(of, st_rng_match);
 136
 137 static struct platform_driver st_rng_driver = {
 138         .driver = {
 139                 .name = "st-hwrandom",
 140                 .of_match_table = of_match_ptr(st_rng_match),
 141         },
 142         .probe = st_rng_probe,
 143         .remove = st_rng_remove
 144 };
 145
 146 module_platform_driver(st_rng_driver);
 147
 148 MODULE_AUTHOR("Pankaj Dev <pankaj.dev@st.com>");
 149 MODULE_LICENSE("GPL v2");