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