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 TRNGMOD		BIT(11)
24 #define RNGSEED1	0x18
25 #define RNGSEED2	0x1C
26 #define RNGRCNT		0x20
27 #define RCNT_MASK	0x7F
28 
29 struct pic32_rng {
30 	void __iomem	*base;
31 	struct hwrng	rng;
32 };
33 
34 /*
35  * The TRNG can generate up to 24Mbps. This is a timeout that should be safe
36  * enough given the instructions in the loop and that the TRNG may not always
37  * be at maximum rate.
38  */
39 #define RNG_TIMEOUT 500
40 
41 static int pic32_rng_read(struct hwrng *rng, void *buf, size_t max,
42 			  bool wait)
43 {
44 	struct pic32_rng *priv = container_of(rng, struct pic32_rng, rng);
45 	u64 *data = buf;
46 	u32 t;
47 	unsigned int timeout = RNG_TIMEOUT;
48 
49 	do {
50 		t = readl(priv->base + RNGRCNT) & RCNT_MASK;
51 		if (t == 64) {
52 			/* TRNG value comes through the seed registers */
53 			*data = ((u64)readl(priv->base + RNGSEED2) << 32) +
54 				readl(priv->base + RNGSEED1);
55 			return 8;
56 		}
57 	} while (wait && --timeout);
58 
59 	return -EIO;
60 }
61 
62 static int pic32_rng_probe(struct platform_device *pdev)
63 {
64 	struct pic32_rng *priv;
65 	struct clk *clk;
66 	u32 v;
67 	int ret;
68 
69 	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
70 	if (!priv)
71 		return -ENOMEM;
72 
73 	priv->base = devm_platform_ioremap_resource(pdev, 0);
74 	if (IS_ERR(priv->base))
75 		return PTR_ERR(priv->base);
76 
77 	clk = devm_clk_get_enabled(&pdev->dev, NULL);
78 	if (IS_ERR(clk))
79 		return PTR_ERR(clk);
80 
81 	/* enable TRNG in enhanced mode */
82 	v = TRNGEN | TRNGMOD;
83 	writel(v, priv->base + RNGCON);
84 
85 	priv->rng.name = pdev->name;
86 	priv->rng.read = pic32_rng_read;
87 
88 	ret = devm_hwrng_register(&pdev->dev, &priv->rng);
89 	if (ret)
90 		return ret;
91 
92 	platform_set_drvdata(pdev, priv);
93 
94 	return 0;
95 }
96 
97 static int pic32_rng_remove(struct platform_device *pdev)
98 {
99 	struct pic32_rng *rng = platform_get_drvdata(pdev);
100 
101 	writel(0, rng->base + RNGCON);
102 	return 0;
103 }
104 
105 static const struct of_device_id pic32_rng_of_match[] __maybe_unused = {
106 	{ .compatible	= "microchip,pic32mzda-rng", },
107 	{ /* sentinel */ }
108 };
109 MODULE_DEVICE_TABLE(of, pic32_rng_of_match);
110 
111 static struct platform_driver pic32_rng_driver = {
112 	.probe		= pic32_rng_probe,
113 	.remove		= pic32_rng_remove,
114 	.driver		= {
115 		.name	= "pic32-rng",
116 		.of_match_table = of_match_ptr(pic32_rng_of_match),
117 	},
118 };
119 
120 module_platform_driver(pic32_rng_driver);
121 
122 MODULE_LICENSE("GPL");
123 MODULE_AUTHOR("Joshua Henderson <joshua.henderson@microchip.com>");
124 MODULE_DESCRIPTION("Microchip PIC32 RNG Driver");
125