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/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
  43struct st_rng_data {
  44        void __iomem    *base;
  45        struct clk      *clk;
  46        struct hwrng    ops;
  47};
  48
  49static 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
  73static 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
 116static 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
 125static const struct of_device_id st_rng_match[] __maybe_unused = {
 126        { .compatible = "st,rng" },
 127        {},
 128};
 129MODULE_DEVICE_TABLE(of, st_rng_match);
 130
 131static 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
 140module_platform_driver(st_rng_driver);
 141
 142MODULE_AUTHOR("Pankaj Dev <pankaj.dev@st.com>");
 143MODULE_LICENSE("GPL v2");
 144