1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * PIC32 RNG driver
4  *
5  * Joshua Henderson <joshua.henderson@microchip.com>
6  * Copyright (C) 2016 Microchip Technology Inc.  All rights reserved.
7  */
8 
9 #include <linux/clk.h>
10 #include <linux/clkdev.h>
11 #include <linux/err.h>
12 #include <linux/hw_random.h>
13 #include <linux/io.h>
14 #include <linux/kernel.h>
15 #include <linux/module.h>
16 #include <linux/of.h>
17 #include <linux/of_device.h>
18 #include <linux/platform_device.h>
19 #include <linux/slab.h>
20 
21 #define RNGCON		0x04
22 #define  TRNGEN		BIT(8)
23 #define  PRNGEN		BIT(9)
24 #define  PRNGCONT	BIT(10)
25 #define  TRNGMOD	BIT(11)
26 #define  SEEDLOAD	BIT(12)
27 #define RNGPOLY1	0x08
28 #define RNGPOLY2	0x0C
29 #define RNGNUMGEN1	0x10
30 #define RNGNUMGEN2	0x14
31 #define RNGSEED1	0x18
32 #define RNGSEED2	0x1C
33 #define RNGRCNT		0x20
34 #define  RCNT_MASK	0x7F
35 
36 struct pic32_rng {
37 	void __iomem	*base;
38 	struct hwrng	rng;
39 	struct clk	*clk;
40 };
41 
42 /*
43  * The TRNG can generate up to 24Mbps. This is a timeout that should be safe
44  * enough given the instructions in the loop and that the TRNG may not always
45  * be at maximum rate.
46  */
47 #define RNG_TIMEOUT 500
48 
49 static int pic32_rng_read(struct hwrng *rng, void *buf, size_t max,
50 			  bool wait)
51 {
52 	struct pic32_rng *priv = container_of(rng, struct pic32_rng, rng);
53 	u64 *data = buf;
54 	u32 t;
55 	unsigned int timeout = RNG_TIMEOUT;
56 
57 	do {
58 		t = readl(priv->base + RNGRCNT) & RCNT_MASK;
59 		if (t == 64) {
60 			/* TRNG value comes through the seed registers */
61 			*data = ((u64)readl(priv->base + RNGSEED2) << 32) +
62 				readl(priv->base + RNGSEED1);
63 			return 8;
64 		}
65 	} while (wait && --timeout);
66 
67 	return -EIO;
68 }
69 
70 static int pic32_rng_probe(struct platform_device *pdev)
71 {
72 	struct pic32_rng *priv;
73 	u32 v;
74 	int ret;
75 
76 	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
77 	if (!priv)
78 		return -ENOMEM;
79 
80 	priv->base = devm_platform_ioremap_resource(pdev, 0);
81 	if (IS_ERR(priv->base))
82 		return PTR_ERR(priv->base);
83 
84 	priv->clk = devm_clk_get(&pdev->dev, NULL);
85 	if (IS_ERR(priv->clk))
86 		return PTR_ERR(priv->clk);
87 
88 	ret = clk_prepare_enable(priv->clk);
89 	if (ret)
90 		return ret;
91 
92 	/* enable TRNG in enhanced mode */
93 	v = TRNGEN | TRNGMOD;
94 	writel(v, priv->base + RNGCON);
95 
96 	priv->rng.name = pdev->name;
97 	priv->rng.read = pic32_rng_read;
98 
99 	ret = hwrng_register(&priv->rng);
100 	if (ret)
101 		goto err_register;
102 
103 	platform_set_drvdata(pdev, priv);
104 
105 	return 0;
106 
107 err_register:
108 	clk_disable_unprepare(priv->clk);
109 	return ret;
110 }
111 
112 static int pic32_rng_remove(struct platform_device *pdev)
113 {
114 	struct pic32_rng *rng = platform_get_drvdata(pdev);
115 
116 	hwrng_unregister(&rng->rng);
117 	writel(0, rng->base + RNGCON);
118 	clk_disable_unprepare(rng->clk);
119 	return 0;
120 }
121 
122 static const struct of_device_id pic32_rng_of_match[] __maybe_unused = {
123 	{ .compatible	= "microchip,pic32mzda-rng", },
124 	{ /* sentinel */ }
125 };
126 MODULE_DEVICE_TABLE(of, pic32_rng_of_match);
127 
128 static struct platform_driver pic32_rng_driver = {
129 	.probe		= pic32_rng_probe,
130 	.remove		= pic32_rng_remove,
131 	.driver		= {
132 		.name	= "pic32-rng",
133 		.of_match_table = of_match_ptr(pic32_rng_of_match),
134 	},
135 };
136 
137 module_platform_driver(pic32_rng_driver);
138 
139 MODULE_LICENSE("GPL");
140 MODULE_AUTHOR("Joshua Henderson <joshua.henderson@microchip.com>");
141 MODULE_DESCRIPTION("Microchip PIC32 RNG Driver");
142