drivers/char/hw_random/histb-rng.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later OR MIT
   2 /*
   3  * Copyright (c) 2023 David Yang
   4  */
   5
   6 #include <linux/err.h>
   7 #include <linux/hw_random.h>
   8 #include <linux/io.h>
   9 #include <linux/iopoll.h>
  10 #include <linux/kernel.h>
  11 #include <linux/mod_devicetable.h>
  12 #include <linux/module.h>
  13 #include <linux/platform_device.h>
  14
  15 #define RNG_CTRL                0x0
  16 #define  RNG_SOURCE                     GENMASK(1, 0)
  17 #define  DROP_ENABLE                    BIT(5)
  18 #define  POST_PROCESS_ENABLE            BIT(7)
  19 #define  POST_PROCESS_DEPTH             GENMASK(15, 8)
  20 #define RNG_NUMBER              0x4
  21 #define RNG_STAT                0x8
  22 #define  DATA_COUNT                     GENMASK(2, 0)   /* max 4 */
  23
  24 struct histb_rng_priv {
  25         struct hwrng rng;
  26         void __iomem *base;
  27 };
  28
  29 /*
  30  * Observed:
  31  * depth = 1 -> ~1ms
  32  * depth = 255 -> ~16ms
  33  */
  34 static int histb_rng_wait(void __iomem *base)
  35 {
  36         u32 val;
  37
  38         return readl_relaxed_poll_timeout(base + RNG_STAT, val,
  39                                           val & DATA_COUNT, 1000, 30 * 1000);
  40 }
  41
  42 static void histb_rng_init(void __iomem *base, unsigned int depth)
  43 {
  44         u32 val;
  45
  46         val = readl_relaxed(base + RNG_CTRL);
  47
  48         val &= ~RNG_SOURCE;
  49         val |= 2;
  50
  51         val &= ~POST_PROCESS_DEPTH;
  52         val |= min(depth, 0xffu) << 8;
  53
  54         val |= POST_PROCESS_ENABLE;
  55         val |= DROP_ENABLE;
  56
  57         writel_relaxed(val, base + RNG_CTRL);
  58 }
  59
  60 static int histb_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
  61 {
  62         struct histb_rng_priv *priv = container_of(rng, typeof(*priv), rng);
  63         void __iomem *base = priv->base;
  64
  65         for (int i = 0; i < max; i += sizeof(u32)) {
  66                 if (!(readl_relaxed(base + RNG_STAT) & DATA_COUNT)) {
  67                         if (!wait)
  68                                 return i;
  69                         if (histb_rng_wait(base)) {
  70                                 pr_err("failed to generate random number, generated %d\n",
  71                                        i);
  72                                 return i ? i : -ETIMEDOUT;
  73                         }
  74                 }
  75                 *(u32 *) (data + i) = readl_relaxed(base + RNG_NUMBER);
  76         }
  77
  78         return max;
  79 }
  80
  81 static unsigned int histb_rng_get_depth(void __iomem *base)
  82 {
  83         return (readl_relaxed(base + RNG_CTRL) & POST_PROCESS_DEPTH) >> 8;
  84 }
  85
  86 static ssize_t
  87 depth_show(struct device *dev, struct device_attribute *attr, char *buf)
  88 {
  89         struct histb_rng_priv *priv = dev_get_drvdata(dev);
  90         void __iomem *base = priv->base;
  91
  92         return sprintf(buf, "%d\n", histb_rng_get_depth(base));
  93 }
  94
  95 static ssize_t
  96 depth_store(struct device *dev, struct device_attribute *attr,
  97             const char *buf, size_t count)
  98 {
  99         struct histb_rng_priv *priv = dev_get_drvdata(dev);
 100         void __iomem *base = priv->base;
 101         unsigned int depth;
 102
 103         if (kstrtouint(buf, 0, &depth))
 104                 return -ERANGE;
 105
 106         histb_rng_init(base, depth);
 107         return count;
 108 }
 109
 110 static DEVICE_ATTR_RW(depth);
 111
 112 static struct attribute *histb_rng_attrs[] = {
 113         &dev_attr_depth.attr,
 114         NULL,
 115 };
 116
 117 ATTRIBUTE_GROUPS(histb_rng);
 118
 119 static int histb_rng_probe(struct platform_device *pdev)
 120 {
 121         struct device *dev = &pdev->dev;
 122         struct histb_rng_priv *priv;
 123         void __iomem *base;
 124         int ret;
 125
 126         priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
 127         if (!priv)
 128                 return -ENOMEM;
 129
 130         base = devm_platform_ioremap_resource(pdev, 0);
 131         if (IS_ERR(base))
 132                 return PTR_ERR(base);
 133
 134         histb_rng_init(base, 144);
 135         if (histb_rng_wait(base)) {
 136                 dev_err(dev, "cannot bring up device\n");
 137                 return -ENODEV;
 138         }
 139
 140         priv->base = base;
 141         priv->rng.name = pdev->name;
 142         priv->rng.read = histb_rng_read;
 143         ret = devm_hwrng_register(dev, &priv->rng);
 144         if (ret) {
 145                 dev_err(dev, "failed to register hwrng: %d\n", ret);
 146                 return ret;
 147         }
 148
 149         platform_set_drvdata(pdev, priv);
 150         dev_set_drvdata(dev, priv);
 151         return 0;
 152 }
 153
 154 static const struct of_device_id histb_rng_of_match[] = {
 155         { .compatible = "hisilicon,histb-rng", },
 156         { }
 157 };
 158 MODULE_DEVICE_TABLE(of, histb_rng_of_match);
 159
 160 static struct platform_driver histb_rng_driver = {
 161         .probe = histb_rng_probe,
 162         .driver = {
 163                 .name = "histb-rng",
 164                 .of_match_table = histb_rng_of_match,
 165                 .dev_groups = histb_rng_groups,
 166         },
 167 };
 168
 169 module_platform_driver(histb_rng_driver);
 170
 171 MODULE_DESCRIPTION("Hisilicon STB random number generator driver");
 172 MODULE_LICENSE("Dual MIT/GPL");
 173 MODULE_AUTHOR("David Yang <[email protected]>");