drivers/char/hw_random/picoxcell-rng.c

   1 /*
   2  * Copyright (c) 2010-2011 Picochip Ltd., Jamie Iles
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License version 2 as
   6  * published by the Free Software Foundation.
   7  *
   8  * All enquiries to support@picochip.com
   9  */
  10 #include <linux/clk.h>
  11 #include <linux/delay.h>
  12 #include <linux/err.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/platform_device.h>
  18
  19 #define DATA_REG_OFFSET         0x0200
  20 #define CSR_REG_OFFSET          0x0278
  21 #define CSR_OUT_EMPTY_MASK      (1 << 24)
  22 #define CSR_FAULT_MASK          (1 << 1)
  23 #define TRNG_BLOCK_RESET_MASK   (1 << 0)
  24 #define TAI_REG_OFFSET          0x0380
  25
  26 /*
  27  * The maximum amount of time in microseconds to spend waiting for data if the
  28  * core wants us to wait.  The TRNG should generate 32 bits every 320ns so a
  29  * timeout of 20us seems reasonable.  The TRNG does builtin tests of the data
  30  * for randomness so we can't always assume there is data present.
  31  */
  32 #define PICO_TRNG_TIMEOUT               20
  33
  34 static void __iomem *rng_base;
  35 static struct clk *rng_clk;
  36 static struct device *rng_dev;
  37
  38 static inline u32 picoxcell_trng_read_csr(void)
  39 {
  40         return __raw_readl(rng_base + CSR_REG_OFFSET);
  41 }
  42
  43 static inline bool picoxcell_trng_is_empty(void)
  44 {
  45         return picoxcell_trng_read_csr() & CSR_OUT_EMPTY_MASK;
  46 }
  47
  48 /*
  49  * Take the random number generator out of reset and make sure the interrupts
  50  * are masked. We shouldn't need to get large amounts of random bytes so just
  51  * poll the status register. The hardware generates 32 bits every 320ns so we
  52  * shouldn't have to wait long enough to warrant waiting for an IRQ.
  53  */
  54 static void picoxcell_trng_start(void)
  55 {
  56         __raw_writel(0, rng_base + TAI_REG_OFFSET);
  57         __raw_writel(0, rng_base + CSR_REG_OFFSET);
  58 }
  59
  60 static void picoxcell_trng_reset(void)
  61 {
  62         __raw_writel(TRNG_BLOCK_RESET_MASK, rng_base + CSR_REG_OFFSET);
  63         __raw_writel(TRNG_BLOCK_RESET_MASK, rng_base + TAI_REG_OFFSET);
  64         picoxcell_trng_start();
  65 }
  66
  67 /*
  68  * Get some random data from the random number generator. The hw_random core
  69  * layer provides us with locking.
  70  */
  71 static int picoxcell_trng_read(struct hwrng *rng, void *buf, size_t max,
  72                                bool wait)
  73 {
  74         int i;
  75
  76         /* Wait for some data to become available. */
  77         for (i = 0; i < PICO_TRNG_TIMEOUT && picoxcell_trng_is_empty(); ++i) {
  78                 if (!wait)
  79                         return 0;
  80
  81                 udelay(1);
  82         }
  83
  84         if (picoxcell_trng_read_csr() & CSR_FAULT_MASK) {
  85                 dev_err(rng_dev, "fault detected, resetting TRNG\n");
  86                 picoxcell_trng_reset();
  87                 return -EIO;
  88         }
  89
  90         if (i == PICO_TRNG_TIMEOUT)
  91                 return 0;
  92
  93         *(u32 *)buf = __raw_readl(rng_base + DATA_REG_OFFSET);
  94         return sizeof(u32);
  95 }
  96
  97 static struct hwrng picoxcell_trng = {
  98         .name           = "picoxcell",
  99         .read           = picoxcell_trng_read,
 100 };
 101
 102 static int picoxcell_trng_probe(struct platform_device *pdev)
 103 {
 104         int ret;
 105         struct resource *mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
 106
 107         if (!mem) {
 108                 dev_warn(&pdev->dev, "no memory resource\n");
 109                 return -ENOMEM;
 110         }
 111
 112         if (!devm_request_mem_region(&pdev->dev, mem->start, resource_size(mem),
 113                                      "picoxcell_trng")) {
 114                 dev_warn(&pdev->dev, "unable to request io mem\n");
 115                 return -EBUSY;
 116         }
 117
 118         rng_base = devm_ioremap(&pdev->dev, mem->start, resource_size(mem));
 119         if (!rng_base) {
 120                 dev_warn(&pdev->dev, "unable to remap io mem\n");
 121                 return -ENOMEM;
 122         }
 123
 124         rng_clk = clk_get(&pdev->dev, NULL);
 125         if (IS_ERR(rng_clk)) {
 126                 dev_warn(&pdev->dev, "no clk\n");
 127                 return PTR_ERR(rng_clk);
 128         }
 129
 130         ret = clk_enable(rng_clk);
 131         if (ret) {
 132                 dev_warn(&pdev->dev, "unable to enable clk\n");
 133                 goto err_enable;
 134         }
 135
 136         picoxcell_trng_start();
 137         ret = hwrng_register(&picoxcell_trng);
 138         if (ret)
 139                 goto err_register;
 140
 141         rng_dev = &pdev->dev;
 142         dev_info(&pdev->dev, "pixoxcell random number generator active\n");
 143
 144         return 0;
 145
 146 err_register:
 147         clk_disable(rng_clk);
 148 err_enable:
 149         clk_put(rng_clk);
 150
 151         return ret;
 152 }
 153
 154 static int picoxcell_trng_remove(struct platform_device *pdev)
 155 {
 156         hwrng_unregister(&picoxcell_trng);
 157         clk_disable(rng_clk);
 158         clk_put(rng_clk);
 159
 160         return 0;
 161 }
 162
 163 #ifdef CONFIG_PM
 164 static int picoxcell_trng_suspend(struct device *dev)
 165 {
 166         clk_disable(rng_clk);
 167
 168         return 0;
 169 }
 170
 171 static int picoxcell_trng_resume(struct device *dev)
 172 {
 173         return clk_enable(rng_clk);
 174 }
 175
 176 static const struct dev_pm_ops picoxcell_trng_pm_ops = {
 177         .suspend        = picoxcell_trng_suspend,
 178         .resume         = picoxcell_trng_resume,
 179 };
 180 #endif /* CONFIG_PM */
 181
 182 static struct platform_driver picoxcell_trng_driver = {
 183         .probe          = picoxcell_trng_probe,
 184         .remove         = picoxcell_trng_remove,
 185         .driver         = {
 186                 .name   = "picoxcell-trng",
 187                 .owner  = THIS_MODULE,
 188 #ifdef CONFIG_PM
 189                 .pm     = &picoxcell_trng_pm_ops,
 190 #endif /* CONFIG_PM */
 191         },
 192 };
 193
 194 module_platform_driver(picoxcell_trng_driver);
 195
 196 MODULE_LICENSE("GPL");
 197 MODULE_AUTHOR("Jamie Iles");
 198 MODULE_DESCRIPTION("Picochip picoXcell TRNG driver");