drivers/char/hw_random/xiphera-trng.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /* Copyright (C) 2020 Xiphera Ltd. */
   3
   4 #include <linux/kernel.h>
   5 #include <linux/module.h>
   6 #include <linux/mod_devicetable.h>
   7 #include <linux/err.h>
   8 #include <linux/io.h>
   9 #include <linux/hw_random.h>
  10 #include <linux/platform_device.h>
  11 #include <linux/delay.h>
  12
  13 #define CONTROL_REG                     0x00000000
  14 #define STATUS_REG                      0x00000004
  15 #define RAND_REG                        0x00000000
  16
  17 #define HOST_TO_TRNG_RESET              0x00000001
  18 #define HOST_TO_TRNG_RELEASE_RESET      0x00000002
  19 #define HOST_TO_TRNG_ENABLE             0x80000000
  20 #define HOST_TO_TRNG_ZEROIZE            0x80000004
  21 #define HOST_TO_TRNG_ACK_ZEROIZE        0x80000008
  22 #define HOST_TO_TRNG_READ               0x8000000F
  23
  24 /* trng statuses */
  25 #define TRNG_ACK_RESET                  0x000000AC
  26 #define TRNG_SUCCESSFUL_STARTUP         0x00000057
  27 #define TRNG_FAILED_STARTUP             0x000000FA
  28 #define TRNG_NEW_RAND_AVAILABLE         0x000000ED
  29
  30 struct xiphera_trng {
  31         void __iomem *mem;
  32         struct hwrng rng;
  33 };
  34
  35 static int xiphera_trng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
  36 {
  37         struct xiphera_trng *trng = container_of(rng, struct xiphera_trng, rng);
  38         int ret = 0;
  39
  40         while (max >= sizeof(u32)) {
  41                 /* check for data */
  42                 if (readl(trng->mem + STATUS_REG) == TRNG_NEW_RAND_AVAILABLE) {
  43                         *(u32 *)buf = readl(trng->mem + RAND_REG);
  44                         /*
  45                          * Inform the trng of the read
  46                          * and re-enable it to produce a new random number
  47                          */
  48                         writel(HOST_TO_TRNG_READ, trng->mem + CONTROL_REG);
  49                         writel(HOST_TO_TRNG_ENABLE, trng->mem + CONTROL_REG);
  50                         ret += sizeof(u32);
  51                         buf += sizeof(u32);
  52                         max -= sizeof(u32);
  53                 } else {
  54                         break;
  55                 }
  56         }
  57         return ret;
  58 }
  59
  60 static int xiphera_trng_probe(struct platform_device *pdev)
  61 {
  62         int ret;
  63         struct xiphera_trng *trng;
  64         struct device *dev = &pdev->dev;
  65
  66         trng = devm_kzalloc(dev, sizeof(*trng), GFP_KERNEL);
  67         if (!trng)
  68                 return -ENOMEM;
  69
  70         trng->mem = devm_platform_ioremap_resource(pdev, 0);
  71         if (IS_ERR(trng->mem))
  72                 return PTR_ERR(trng->mem);
  73
  74         /*
  75          * the trng needs to be reset first which might not happen in time,
  76          * hence we incorporate a small delay to ensure proper behaviour
  77          */
  78         writel(HOST_TO_TRNG_RESET, trng->mem + CONTROL_REG);
  79         usleep_range(100, 200);
  80
  81         if (readl(trng->mem + STATUS_REG) != TRNG_ACK_RESET) {
  82                 /*
  83                  * there is a small chance the trng is just not ready yet,
  84                  * so we try one more time. If the second time fails, we give up
  85                  */
  86                 usleep_range(100, 200);
  87                 if (readl(trng->mem + STATUS_REG) != TRNG_ACK_RESET) {
  88                         dev_err(dev, "failed to reset the trng ip\n");
  89                         return -ENODEV;
  90                 }
  91         }
  92
  93         /*
  94          * once again, to ensure proper behaviour we sleep
  95          * for a while after zeroizing the trng
  96          */
  97         writel(HOST_TO_TRNG_RELEASE_RESET, trng->mem + CONTROL_REG);
  98         writel(HOST_TO_TRNG_ENABLE, trng->mem + CONTROL_REG);
  99         writel(HOST_TO_TRNG_ZEROIZE, trng->mem + CONTROL_REG);
 100         msleep(20);
 101
 102         if (readl(trng->mem + STATUS_REG) != TRNG_SUCCESSFUL_STARTUP) {
 103                 /* diagnose the reason for the failure */
 104                 if (readl(trng->mem + STATUS_REG) == TRNG_FAILED_STARTUP) {
 105                         dev_err(dev, "trng ip startup-tests failed\n");
 106                         return -ENODEV;
 107                 }
 108                 dev_err(dev, "startup-tests yielded no response\n");
 109                 return -ENODEV;
 110         }
 111
 112         writel(HOST_TO_TRNG_ACK_ZEROIZE, trng->mem + CONTROL_REG);
 113
 114         trng->rng.name = pdev->name;
 115         trng->rng.read = xiphera_trng_read;
 116         trng->rng.quality = 900;
 117
 118         ret = devm_hwrng_register(dev, &trng->rng);
 119         if (ret) {
 120                 dev_err(dev, "failed to register rng device: %d\n", ret);
 121                 return ret;
 122         }
 123
 124         return 0;
 125 }
 126
 127 static const struct of_device_id xiphera_trng_of_match[] = {
 128         { .compatible = "xiphera,xip8001b-trng", },
 129         {},
 130 };
 131 MODULE_DEVICE_TABLE(of, xiphera_trng_of_match);
 132
 133 static struct platform_driver xiphera_trng_driver = {
 134         .driver = {
 135                 .name = "xiphera-trng",
 136                 .of_match_table = xiphera_trng_of_match,
 137         },
 138         .probe = xiphera_trng_probe,
 139 };
 140
 141 module_platform_driver(xiphera_trng_driver);
 142
 143 MODULE_LICENSE("GPL");
 144 MODULE_AUTHOR("Atte Tommiska");
 145 MODULE_DESCRIPTION("Xiphera FPGA-based true random number generator driver");