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/module.h>
  11 #include <linux/kernel.h>
  12 #include <linux/init.h>
  13 #include <linux/delay.h>
  14 #include <linux/io.h>
  15 #include <linux/platform_device.h>
  16 #include <linux/hw_random.h>
  17
  18 #define TX4939_RNG_RCSR         0x00000000
  19 #define TX4939_RNG_ROR(n)       (0x00000018 + (n) * 8)
  20
  21 #define TX4939_RNG_RCSR_INTE    0x00000008
  22 #define TX4939_RNG_RCSR_RST     0x00000004
  23 #define TX4939_RNG_RCSR_FIN     0x00000002
  24 #define TX4939_RNG_RCSR_ST      0x00000001
  25
  26 struct tx4939_rng {
  27         struct hwrng rng;
  28         void __iomem *base;
  29         u64 databuf[3];
  30         unsigned int data_avail;
  31 };
  32
  33 static void rng_io_start(void)
  34 {
  35 #ifndef CONFIG_64BIT
  36         /*
  37          * readq is reading a 64-bit register using a 64-bit load.  On
  38          * a 32-bit kernel however interrupts or any other processor
  39          * exception would clobber the upper 32-bit of the processor
  40          * register so interrupts need to be disabled.
  41          */
  42         local_irq_disable();
  43 #endif
  44 }
  45
  46 static void rng_io_end(void)
  47 {
  48 #ifndef CONFIG_64BIT
  49         local_irq_enable();
  50 #endif
  51 }
  52
  53 static u64 read_rng(void __iomem *base, unsigned int offset)
  54 {
  55         return ____raw_readq(base + offset);
  56 }
  57
  58 static void write_rng(u64 val, void __iomem *base, unsigned int offset)
  59 {
  60         return ____raw_writeq(val, base + offset);
  61 }
  62
  63 static int tx4939_rng_data_present(struct hwrng *rng, int wait)
  64 {
  65         struct tx4939_rng *rngdev = container_of(rng, struct tx4939_rng, rng);
  66         int i;
  67
  68         if (rngdev->data_avail)
  69                 return rngdev->data_avail;
  70         for (i = 0; i < 20; i++) {
  71                 rng_io_start();
  72                 if (!(read_rng(rngdev->base, TX4939_RNG_RCSR)
  73                       & TX4939_RNG_RCSR_ST)) {
  74                         rngdev->databuf[0] =
  75                                 read_rng(rngdev->base, TX4939_RNG_ROR(0));
  76                         rngdev->databuf[1] =
  77                                 read_rng(rngdev->base, TX4939_RNG_ROR(1));
  78                         rngdev->databuf[2] =
  79                                 read_rng(rngdev->base, TX4939_RNG_ROR(2));
  80                         rngdev->data_avail =
  81                                 sizeof(rngdev->databuf) / sizeof(u32);
  82                         /* Start RNG */
  83                         write_rng(TX4939_RNG_RCSR_ST,
  84                                   rngdev->base, TX4939_RNG_RCSR);
  85                         wait = 0;
  86                 }
  87                 rng_io_end();
  88                 if (!wait)
  89                         break;
  90                 /* 90 bus clock cycles by default for generation */
  91                 ndelay(90 * 5);
  92         }
  93         return rngdev->data_avail;
  94 }
  95
  96 static int tx4939_rng_data_read(struct hwrng *rng, u32 *buffer)
  97 {
  98         struct tx4939_rng *rngdev = container_of(rng, struct tx4939_rng, rng);
  99
 100         rngdev->data_avail--;
 101         *buffer = *((u32 *)&rngdev->databuf + rngdev->data_avail);
 102         return sizeof(u32);
 103 }
 104
 105 static int __init tx4939_rng_probe(struct platform_device *dev)
 106 {
 107         struct tx4939_rng *rngdev;
 108         struct resource *r;
 109         int i;
 110
 111         r = platform_get_resource(dev, IORESOURCE_MEM, 0);
 112         if (!r)
 113                 return -EBUSY;
 114         rngdev = devm_kzalloc(&dev->dev, sizeof(*rngdev), GFP_KERNEL);
 115         if (!rngdev)
 116                 return -ENOMEM;
 117         if (!devm_request_mem_region(&dev->dev, r->start, resource_size(r),
 118                                      dev_name(&dev->dev)))
 119                 return -EBUSY;
 120         rngdev->base = devm_ioremap(&dev->dev, r->start, resource_size(r));
 121         if (!rngdev->base)
 122                 return -EBUSY;
 123
 124         rngdev->rng.name = dev_name(&dev->dev);
 125         rngdev->rng.data_present = tx4939_rng_data_present;
 126         rngdev->rng.data_read = tx4939_rng_data_read;
 127
 128         rng_io_start();
 129         /* Reset RNG */
 130         write_rng(TX4939_RNG_RCSR_RST, rngdev->base, TX4939_RNG_RCSR);
 131         write_rng(0, rngdev->base, TX4939_RNG_RCSR);
 132         /* Start RNG */
 133         write_rng(TX4939_RNG_RCSR_ST, rngdev->base, TX4939_RNG_RCSR);
 134         rng_io_end();
 135         /*
 136          * Drop first two results.  From the datasheet:
 137          * The quality of the random numbers generated immediately
 138          * after reset can be insufficient.  Therefore, do not use
 139          * random numbers obtained from the first and second
 140          * generations; use the ones from the third or subsequent
 141          * generation.
 142          */
 143         for (i = 0; i < 2; i++) {
 144                 rngdev->data_avail = 0;
 145                 if (!tx4939_rng_data_present(&rngdev->rng, 1))
 146                         return -EIO;
 147         }
 148
 149         platform_set_drvdata(dev, rngdev);
 150         return hwrng_register(&rngdev->rng);
 151 }
 152
 153 static int __exit tx4939_rng_remove(struct platform_device *dev)
 154 {
 155         struct tx4939_rng *rngdev = platform_get_drvdata(dev);
 156
 157         hwrng_unregister(&rngdev->rng);
 158         platform_set_drvdata(dev, NULL);
 159         return 0;
 160 }
 161
 162 static struct platform_driver tx4939_rng_driver = {
 163         .driver         = {
 164                 .name   = "tx4939-rng",
 165                 .owner  = THIS_MODULE,
 166         },
 167         .remove = tx4939_rng_remove,
 168 };
 169
 170 static int __init tx4939rng_init(void)
 171 {
 172         return platform_driver_probe(&tx4939_rng_driver, tx4939_rng_probe);
 173 }
 174
 175 static void __exit tx4939rng_exit(void)
 176 {
 177         platform_driver_unregister(&tx4939_rng_driver);
 178 }
 179
 180 module_init(tx4939rng_init);
 181 module_exit(tx4939rng_exit);
 182
 183 MODULE_DESCRIPTION("H/W Random Number Generator (RNG) driver for TX4939");
 184 MODULE_LICENSE("GPL");