LXR linux/drivers/char/hw

   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
  42struct st_rng_data {
  43        void __iomem    *base;
  44        struct clk      *clk;
  45        struct hwrng    ops;
  46};
  47
  48static 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
  72static int st_rng_probe(struct platform_device *pdev)
  73{
  74        struct st_rng_data *ddata;
  75        struct resource *res;
  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        res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
  85        base = devm_ioremap_resource(&pdev->dev, res);
  86        if (IS_ERR(base))
  87                return PTR_ERR(base);
  88
  89        clk = devm_clk_get(&pdev->dev, NULL);
  90        if (IS_ERR(clk))
  91                return PTR_ERR(clk);
  92
  93        ret = clk_prepare_enable(clk);
  94        if (ret)
  95                return ret;
  96
  97        ddata->ops.priv = (unsigned long)ddata;
  98        ddata->ops.read = st_rng_read;
  99        ddata->ops.name = pdev->name;
 100        ddata->base     = base;
 101        ddata->clk      = clk;
 102
 103        dev_set_drvdata(&pdev->dev, ddata);
 104
 105        ret = hwrng_register(&ddata->ops);
 106        if (ret) {
 107                dev_err(&pdev->dev, "Failed to register HW RNG\n");
 108                clk_disable_unprepare(clk);
 109                return ret;
 110        }
 111
 112        dev_info(&pdev->dev, "Successfully registered HW RNG\n");
 113
 114        return 0;
 115}
 116
 117static int st_rng_remove(struct platform_device *pdev)
 118{
 119        struct st_rng_data *ddata = dev_get_drvdata(&pdev->dev);
 120
 121        hwrng_unregister(&ddata->ops);
 122
 123        clk_disable_unprepare(ddata->clk);
 124
 125        return 0;
 126}
 127
 128static const struct of_device_id st_rng_match[] = {
 129        { .compatible = "st,rng" },
 130        {},
 131};
 132MODULE_DEVICE_TABLE(of, st_rng_match);
 133
 134static struct platform_driver st_rng_driver = {
 135        .driver = {
 136                .name = "st-hwrandom",
 137                .of_match_table = of_match_ptr(st_rng_match),
 138        },
 139        .probe = st_rng_probe,
 140        .remove = st_rng_remove
 141};
 142
 143module_platform_driver(st_rng_driver);
 144
 145MODULE_AUTHOR("Pankaj Dev <pankaj.dev@st.com>");
 146MODULE_LICENSE("GPL v2");
 147