LXR linux/drivers/char/hw_random/tx4939-rng.c

   1/*
   2 * RNG driver for TX4939 Random Number Generators (RNG)
   3 *
   4 * Copyright (C) 2009 Atsushi Nemoto <anemo@mba.ocn.ne.jp>
   5 *
   6 * This file is subject to the terms and conditions of the GNU General Public
   7 * License.  See the file "COPYING" in the main directory of this archive
   8 * for more details.
   9 */
  10#include <linux/err.h>
  11#include <linux/module.h>
  12#include <linux/kernel.h>
  13#include <linux/init.h>
  14#include <linux/delay.h>
  15#include <linux/io.h>
  16#include <linux/platform_device.h>
  17#include <linux/hw_random.h>
  18#include <linux/gfp.h>
  19
  20#define TX4939_RNG_RCSR         0x00000000
  21#define TX4939_RNG_ROR(n)       (0x00000018 + (n) * 8)
  22
  23#define TX4939_RNG_RCSR_INTE    0x00000008
  24#define TX4939_RNG_RCSR_RST     0x00000004
  25#define TX4939_RNG_RCSR_FIN     0x00000002
  26#define TX4939_RNG_RCSR_ST      0x00000001
  27
  28struct tx4939_rng {
  29        struct hwrng rng;
  30        void __iomem *base;
  31        u64 databuf[3];
  32        unsigned int data_avail;
  33};
  34
  35static void rng_io_start(void)
  36{
  37#ifndef CONFIG_64BIT
  38        /*
  39         * readq is reading a 64-bit register using a 64-bit load.  On
  40         * a 32-bit kernel however interrupts or any other processor
  41         * exception would clobber the upper 32-bit of the processor
  42         * register so interrupts need to be disabled.
  43         */
  44        local_irq_disable();
  45#endif
  46}
  47
  48static void rng_io_end(void)
  49{
  50#ifndef CONFIG_64BIT
  51        local_irq_enable();
  52#endif
  53}
  54
  55static u64 read_rng(void __iomem *base, unsigned int offset)
  56{
  57        return ____raw_readq(base + offset);
  58}
  59
  60static void write_rng(u64 val, void __iomem *base, unsigned int offset)
  61{
  62        return ____raw_writeq(val, base + offset);
  63}
  64
  65static int tx4939_rng_data_present(struct hwrng *rng, int wait)
  66{
  67        struct tx4939_rng *rngdev = container_of(rng, struct tx4939_rng, rng);
  68        int i;
  69
  70        if (rngdev->data_avail)
  71                return rngdev->data_avail;
  72        for (i = 0; i < 20; i++) {
  73                rng_io_start();
  74                if (!(read_rng(rngdev->base, TX4939_RNG_RCSR)
  75                      & TX4939_RNG_RCSR_ST)) {
  76                        rngdev->databuf[0] =
  77                                read_rng(rngdev->base, TX4939_RNG_ROR(0));
  78                        rngdev->databuf[1] =
  79                                read_rng(rngdev->base, TX4939_RNG_ROR(1));
  80                        rngdev->databuf[2] =
  81                                read_rng(rngdev->base, TX4939_RNG_ROR(2));
  82                        rngdev->data_avail =
  83                                sizeof(rngdev->databuf) / sizeof(u32);
  84                        /* Start RNG */
  85                        write_rng(TX4939_RNG_RCSR_ST,
  86                                  rngdev->base, TX4939_RNG_RCSR);
  87                        wait = 0;
  88                }
  89                rng_io_end();
  90                if (!wait)
  91                        break;
  92                /* 90 bus clock cycles by default for generation */
  93                ndelay(90 * 5);
  94        }
  95        return rngdev->data_avail;
  96}
  97
  98static int tx4939_rng_data_read(struct hwrng *rng, u32 *buffer)
  99{
 100        struct tx4939_rng *rngdev = container_of(rng, struct tx4939_rng, rng);
 101
 102        rngdev->data_avail--;
 103        *buffer = *((u32 *)&rngdev->databuf + rngdev->data_avail);
 104        return sizeof(u32);
 105}
 106
 107static int __init tx4939_rng_probe(struct platform_device *dev)
 108{
 109        struct tx4939_rng *rngdev;
 110        int i;
 111
 112        rngdev = devm_kzalloc(&dev->dev, sizeof(*rngdev), GFP_KERNEL);
 113        if (!rngdev)
 114                return -ENOMEM;
 115        rngdev->base = devm_platform_ioremap_resource(dev, 0);
 116        if (IS_ERR(rngdev->base))
 117                return PTR_ERR(rngdev->base);
 118
 119        rngdev->rng.name = dev_name(&dev->dev);
 120        rngdev->rng.data_present = tx4939_rng_data_present;
 121        rngdev->rng.data_read = tx4939_rng_data_read;
 122
 123        rng_io_start();
 124        /* Reset RNG */
 125        write_rng(TX4939_RNG_RCSR_RST, rngdev->base, TX4939_RNG_RCSR);
 126        write_rng(0, rngdev->base, TX4939_RNG_RCSR);
 127        /* Start RNG */
 128        write_rng(TX4939_RNG_RCSR_ST, rngdev->base, TX4939_RNG_RCSR);
 129        rng_io_end();
 130        /*
 131         * Drop first two results.  From the datasheet:
 132         * The quality of the random numbers generated immediately
 133         * after reset can be insufficient.  Therefore, do not use
 134         * random numbers obtained from the first and second
 135         * generations; use the ones from the third or subsequent
 136         * generation.
 137         */
 138        for (i = 0; i < 2; i++) {
 139                rngdev->data_avail = 0;
 140                if (!tx4939_rng_data_present(&rngdev->rng, 1))
 141                        return -EIO;
 142        }
 143
 144        platform_set_drvdata(dev, rngdev);
 145        return devm_hwrng_register(&dev->dev, &rngdev->rng);
 146}
 147
 148static struct platform_driver tx4939_rng_driver = {
 149        .driver         = {
 150                .name   = "tx4939-rng",
 151        },
 152};
 153
 154module_platform_driver_probe(tx4939_rng_driver, tx4939_rng_probe);
 155
 156MODULE_DESCRIPTION("H/W Random Number Generator (RNG) driver for TX4939");
 157MODULE_LICENSE("GPL");
 158