1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Copyright (c) 2024 Broadcom
4 */
5
6 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
7
8 #include <linux/module.h>
9 #include <linux/kernel.h>
10 #include <linux/io.h>
11 #include <linux/delay.h>
12 #include <linux/platform_device.h>
13 #include <linux/random.h>
14 #include <linux/hw_random.h>
15
16 #define HOST_REV_ID 0x00
17 #define HOST_FIFO_DEPTH 0x04
18 #define HOST_FIFO_COUNT 0x08
19 #define HOST_FIFO_THRESHOLD 0x0c
20 #define HOST_FIFO_DATA 0x10
21
22 #define HOST_FIFO_COUNT_MASK 0xffff
23
24 /* Delay range in microseconds */
25 #define FIFO_DELAY_MIN_US 3
26 #define FIFO_DELAY_MAX_US 7
27 #define FIFO_DELAY_MAX_COUNT 10
28
29 struct bcm74110_priv {
30 void __iomem *base;
31 };
32
bcm74110_rng_fifo_count(void __iomem * mem)33 static inline int bcm74110_rng_fifo_count(void __iomem *mem)
34 {
35 return readl_relaxed(mem) & HOST_FIFO_COUNT_MASK;
36 }
37
bcm74110_rng_read(struct hwrng * rng,void * buf,size_t max,bool wait)38 static int bcm74110_rng_read(struct hwrng *rng, void *buf, size_t max,
39 bool wait)
40 {
41 struct bcm74110_priv *priv = (struct bcm74110_priv *)rng->priv;
42 void __iomem *fc_addr = priv->base + HOST_FIFO_COUNT;
43 void __iomem *fd_addr = priv->base + HOST_FIFO_DATA;
44 unsigned underrun_count = 0;
45 u32 max_words = max / sizeof(u32);
46 u32 num_words;
47 unsigned i;
48
49 /*
50 * We need to check how many words are available in the RNG FIFO. If
51 * there aren't any, we need to wait for some to become available.
52 */
53 while ((num_words = bcm74110_rng_fifo_count(fc_addr)) == 0) {
54 if (!wait)
55 return 0;
56 /*
57 * As a precaution, limit how long we wait. If the FIFO doesn't
58 * refill within the allotted time, return 0 (=no data) to the
59 * caller.
60 */
61 if (likely(underrun_count < FIFO_DELAY_MAX_COUNT))
62 usleep_range(FIFO_DELAY_MIN_US, FIFO_DELAY_MAX_US);
63 else
64 return 0;
65 underrun_count++;
66 }
67 if (num_words > max_words)
68 num_words = max_words;
69
70 /* Bail early if we run out of random numbers unexpectedly */
71 for (i = 0; i < num_words && bcm74110_rng_fifo_count(fc_addr) > 0; i++)
72 ((u32 *)buf)[i] = readl_relaxed(fd_addr);
73
74 return i * sizeof(u32);
75 }
76
77 static struct hwrng bcm74110_hwrng = {
78 .read = bcm74110_rng_read,
79 };
80
bcm74110_rng_probe(struct platform_device * pdev)81 static int bcm74110_rng_probe(struct platform_device *pdev)
82 {
83 struct device *dev = &pdev->dev;
84 struct bcm74110_priv *priv;
85 int rc;
86
87 priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
88 if (!priv)
89 return -ENOMEM;
90
91 bcm74110_hwrng.name = pdev->name;
92 bcm74110_hwrng.priv = (unsigned long)priv;
93
94 priv->base = devm_platform_ioremap_resource(pdev, 0);
95 if (IS_ERR(priv->base))
96 return PTR_ERR(priv->base);
97
98 rc = devm_hwrng_register(dev, &bcm74110_hwrng);
99 if (rc)
100 dev_err(dev, "hwrng registration failed (%d)\n", rc);
101 else
102 dev_info(dev, "hwrng registered\n");
103
104 return rc;
105 }
106
107 static const struct of_device_id bcm74110_rng_match[] = {
108 { .compatible = "brcm,bcm74110-rng", },
109 {},
110 };
111 MODULE_DEVICE_TABLE(of, bcm74110_rng_match);
112
113 static struct platform_driver bcm74110_rng_driver = {
114 .driver = {
115 .name = KBUILD_MODNAME,
116 .of_match_table = bcm74110_rng_match,
117 },
118 .probe = bcm74110_rng_probe,
119 };
120 module_platform_driver(bcm74110_rng_driver);
121
122 MODULE_AUTHOR("Markus Mayer <mmayer@broadcom.com>");
123 MODULE_DESCRIPTION("BCM 74110 Random Number Generator (RNG) driver");
124 MODULE_LICENSE("GPL v2");
125