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/mod_devicetable.h>
10 #include <linux/kernel.h>
11 #include <linux/io.h>
12 #include <linux/delay.h>
13 #include <linux/platform_device.h>
14 #include <linux/random.h>
15 #include <linux/hw_random.h>
16
17 #define HOST_REV_ID 0x00
18 #define HOST_FIFO_DEPTH 0x04
19 #define HOST_FIFO_COUNT 0x08
20 #define HOST_FIFO_THRESHOLD 0x0c
21 #define HOST_FIFO_DATA 0x10
22
23 #define HOST_FIFO_COUNT_MASK 0xffff
24
25 /* Delay range in microseconds */
26 #define FIFO_DELAY_MIN_US 3
27 #define FIFO_DELAY_MAX_US 7
28 #define FIFO_DELAY_MAX_COUNT 10
29
30 struct bcm74110_priv {
31 void __iomem *base;
32 };
33
bcm74110_rng_fifo_count(void __iomem * mem)34 static inline int bcm74110_rng_fifo_count(void __iomem *mem)
35 {
36 return readl_relaxed(mem) & HOST_FIFO_COUNT_MASK;
37 }
38
bcm74110_rng_read(struct hwrng * rng,void * buf,size_t max,bool wait)39 static int bcm74110_rng_read(struct hwrng *rng, void *buf, size_t max,
40 bool wait)
41 {
42 struct bcm74110_priv *priv = (struct bcm74110_priv *)rng->priv;
43 void __iomem *fc_addr = priv->base + HOST_FIFO_COUNT;
44 void __iomem *fd_addr = priv->base + HOST_FIFO_DATA;
45 unsigned underrun_count = 0;
46 u32 max_words = max / sizeof(u32);
47 u32 num_words;
48 unsigned i;
49
50 /*
51 * We need to check how many words are available in the RNG FIFO. If
52 * there aren't any, we need to wait for some to become available.
53 */
54 while ((num_words = bcm74110_rng_fifo_count(fc_addr)) == 0) {
55 if (!wait)
56 return 0;
57 /*
58 * As a precaution, limit how long we wait. If the FIFO doesn't
59 * refill within the allotted time, return 0 (=no data) to the
60 * caller.
61 */
62 if (likely(underrun_count < FIFO_DELAY_MAX_COUNT))
63 usleep_range(FIFO_DELAY_MIN_US, FIFO_DELAY_MAX_US);
64 else
65 return 0;
66 underrun_count++;
67 }
68 if (num_words > max_words)
69 num_words = max_words;
70
71 /* Bail early if we run out of random numbers unexpectedly */
72 for (i = 0; i < num_words && bcm74110_rng_fifo_count(fc_addr) > 0; i++)
73 ((u32 *)buf)[i] = readl_relaxed(fd_addr);
74
75 return i * sizeof(u32);
76 }
77
78 static struct hwrng bcm74110_hwrng = {
79 .read = bcm74110_rng_read,
80 };
81
bcm74110_rng_probe(struct platform_device * pdev)82 static int bcm74110_rng_probe(struct platform_device *pdev)
83 {
84 struct device *dev = &pdev->dev;
85 struct bcm74110_priv *priv;
86 int rc;
87
88 priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
89 if (!priv)
90 return -ENOMEM;
91
92 bcm74110_hwrng.name = pdev->name;
93 bcm74110_hwrng.priv = (unsigned long)priv;
94
95 priv->base = devm_platform_ioremap_resource(pdev, 0);
96 if (IS_ERR(priv->base))
97 return PTR_ERR(priv->base);
98
99 rc = devm_hwrng_register(dev, &bcm74110_hwrng);
100 if (rc)
101 dev_err(dev, "hwrng registration failed (%d)\n", rc);
102 else
103 dev_info(dev, "hwrng registered\n");
104
105 return rc;
106 }
107
108 static const struct of_device_id bcm74110_rng_match[] = {
109 { .compatible = "brcm,bcm74110-rng", },
110 {},
111 };
112 MODULE_DEVICE_TABLE(of, bcm74110_rng_match);
113
114 static struct platform_driver bcm74110_rng_driver = {
115 .driver = {
116 .name = KBUILD_MODNAME,
117 .of_match_table = bcm74110_rng_match,
118 },
119 .probe = bcm74110_rng_probe,
120 };
121 module_platform_driver(bcm74110_rng_driver);
122
123 MODULE_AUTHOR("Markus Mayer <[email protected]>");
124 MODULE_DESCRIPTION("BCM 74110 Random Number Generator (RNG) driver");
125 MODULE_LICENSE("GPL v2");
126