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         if (max < sizeof(u16))
  58                 return -EINVAL;
  59
  60         /* Wait until FIFO is full - max 4uS*/
  61         for (i = 0; i < ST_RNG_FILL_FIFO_TIMEOUT; i++) {
  62                 status = readl_relaxed(ddata->base + ST_RNG_STATUS_REG);
  63                 if (status & ST_RNG_STATUS_FIFO_FULL)
  64                         break;
  65                 udelay(1);
  66         }
  67
  68         if (i == ST_RNG_FILL_FIFO_TIMEOUT)
  69                 return 0;
  70
  71         for (i = 0; i < ST_RNG_FIFO_SIZE && i < max; i += 2)
  72                 *(u16 *)(data + i) =
  73                         readl_relaxed(ddata->base + ST_RNG_DATA_REG);
  74
  75         return i;       /* No of bytes read */
  76 }
  77
  78 static int st_rng_probe(struct platform_device *pdev)
  79 {
  80         struct st_rng_data *ddata;
  81         struct resource *res;
  82         struct clk *clk;
  83         void __iomem *base;
  84         int ret;
  85
  86         ddata = devm_kzalloc(&pdev->dev, sizeof(*ddata), GFP_KERNEL);
  87         if (!ddata)
  88                 return -ENOMEM;
  89
  90         res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
  91         base = devm_ioremap_resource(&pdev->dev, res);
  92         if (IS_ERR(base))
  93                 return PTR_ERR(base);
  94
  95         clk = devm_clk_get(&pdev->dev, NULL);
  96         if (IS_ERR(clk))
  97                 return PTR_ERR(clk);
  98
  99         ret = clk_prepare_enable(clk);
 100         if (ret)
 101                 return ret;
 102
 103         ddata->ops.priv = (unsigned long)ddata;
 104         ddata->ops.read = st_rng_read;
 105         ddata->ops.name = pdev->name;
 106         ddata->base     = base;
 107         ddata->clk      = clk;
 108
 109         dev_set_drvdata(&pdev->dev, ddata);
 110
 111         ret = hwrng_register(&ddata->ops);
 112         if (ret) {
 113                 dev_err(&pdev->dev, "Failed to register HW RNG\n");
 114                 return ret;
 115         }
 116
 117         dev_info(&pdev->dev, "Successfully registered HW RNG\n");
 118
 119         return 0;
 120 }
 121
 122 static int st_rng_remove(struct platform_device *pdev)
 123 {
 124         struct st_rng_data *ddata = dev_get_drvdata(&pdev->dev);
 125
 126         hwrng_unregister(&ddata->ops);
 127
 128         clk_disable_unprepare(ddata->clk);
 129
 130         return 0;
 131 }
 132
 133 static const struct of_device_id st_rng_match[] = {
 134         { .compatible = "st,rng" },
 135         {},
 136 };
 137 MODULE_DEVICE_TABLE(of, st_rng_match);
 138
 139 static struct platform_driver st_rng_driver = {
 140         .driver = {
 141                 .name = "st-hwrandom",
 142                 .of_match_table = of_match_ptr(st_rng_match),
 143         },
 144         .probe = st_rng_probe,
 145         .remove = st_rng_remove
 146 };
 147
 148 module_platform_driver(st_rng_driver);
 149
 150 MODULE_AUTHOR("Pankaj Dev <pankaj.dev@st.com>");
 151 MODULE_LICENSE("GPL v2");