1 /*
2  * PIC32 RNG driver
3  *
4  * Joshua Henderson <joshua.henderson@microchip.com>
5  * Copyright (C) 2016 Microchip Technology Inc.  All rights reserved.
6  *
7  * This program is free software; you can distribute it and/or modify it
8  * under the terms of the GNU General Public License (Version 2) as
9  * published by the Free Software Foundation.
10  *
11  * This program is distributed in the hope it will be useful, but WITHOUT
12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14  * for more details.
15  */
16 
17 #include <linux/clk.h>
18 #include <linux/clkdev.h>
19 #include <linux/err.h>
20 #include <linux/hw_random.h>
21 #include <linux/io.h>
22 #include <linux/kernel.h>
23 #include <linux/module.h>
24 #include <linux/of.h>
25 #include <linux/of_device.h>
26 #include <linux/platform_device.h>
27 #include <linux/slab.h>
28 
29 #define RNGCON		0x04
30 #define  TRNGEN		BIT(8)
31 #define  PRNGEN		BIT(9)
32 #define  PRNGCONT	BIT(10)
33 #define  TRNGMOD	BIT(11)
34 #define  SEEDLOAD	BIT(12)
35 #define RNGPOLY1	0x08
36 #define RNGPOLY2	0x0C
37 #define RNGNUMGEN1	0x10
38 #define RNGNUMGEN2	0x14
39 #define RNGSEED1	0x18
40 #define RNGSEED2	0x1C
41 #define RNGRCNT		0x20
42 #define  RCNT_MASK	0x7F
43 
44 struct pic32_rng {
45 	void __iomem	*base;
46 	struct hwrng	rng;
47 	struct clk	*clk;
48 };
49 
50 /*
51  * The TRNG can generate up to 24Mbps. This is a timeout that should be safe
52  * enough given the instructions in the loop and that the TRNG may not always
53  * be at maximum rate.
54  */
55 #define RNG_TIMEOUT 500
56 
57 static int pic32_rng_read(struct hwrng *rng, void *buf, size_t max,
58 			  bool wait)
59 {
60 	struct pic32_rng *priv = container_of(rng, struct pic32_rng, rng);
61 	u64 *data = buf;
62 	u32 t;
63 	unsigned int timeout = RNG_TIMEOUT;
64 
65 	do {
66 		t = readl(priv->base + RNGRCNT) & RCNT_MASK;
67 		if (t == 64) {
68 			/* TRNG value comes through the seed registers */
69 			*data = ((u64)readl(priv->base + RNGSEED2) << 32) +
70 				readl(priv->base + RNGSEED1);
71 			return 8;
72 		}
73 	} while (wait && --timeout);
74 
75 	return -EIO;
76 }
77 
78 static int pic32_rng_probe(struct platform_device *pdev)
79 {
80 	struct pic32_rng *priv;
81 	struct resource *res;
82 	u32 v;
83 	int ret;
84 
85 	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
86 	if (!priv)
87 		return -ENOMEM;
88 
89 	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
90 	priv->base = devm_ioremap_resource(&pdev->dev, res);
91 	if (IS_ERR(priv->base))
92 		return PTR_ERR(priv->base);
93 
94 	priv->clk = devm_clk_get(&pdev->dev, NULL);
95 	if (IS_ERR(priv->clk))
96 		return PTR_ERR(priv->clk);
97 
98 	ret = clk_prepare_enable(priv->clk);
99 	if (ret)
100 		return ret;
101 
102 	/* enable TRNG in enhanced mode */
103 	v = TRNGEN | TRNGMOD;
104 	writel(v, priv->base + RNGCON);
105 
106 	priv->rng.name = pdev->name;
107 	priv->rng.read = pic32_rng_read;
108 
109 	ret = hwrng_register(&priv->rng);
110 	if (ret)
111 		goto err_register;
112 
113 	platform_set_drvdata(pdev, priv);
114 
115 	return 0;
116 
117 err_register:
118 	clk_disable_unprepare(priv->clk);
119 	return ret;
120 }
121 
122 static int pic32_rng_remove(struct platform_device *pdev)
123 {
124 	struct pic32_rng *rng = platform_get_drvdata(pdev);
125 
126 	hwrng_unregister(&rng->rng);
127 	writel(0, rng->base + RNGCON);
128 	clk_disable_unprepare(rng->clk);
129 	return 0;
130 }
131 
132 static const struct of_device_id pic32_rng_of_match[] = {
133 	{ .compatible	= "microchip,pic32mzda-rng", },
134 	{ /* sentinel */ }
135 };
136 MODULE_DEVICE_TABLE(of, pic32_rng_of_match);
137 
138 static struct platform_driver pic32_rng_driver = {
139 	.probe		= pic32_rng_probe,
140 	.remove		= pic32_rng_remove,
141 	.driver		= {
142 		.name	= "pic32-rng",
143 		.of_match_table = of_match_ptr(pic32_rng_of_match),
144 	},
145 };
146 
147 module_platform_driver(pic32_rng_driver);
148 
149 MODULE_LICENSE("GPL");
150 MODULE_AUTHOR("Joshua Henderson <joshua.henderson@microchip.com>");
151 MODULE_DESCRIPTION("Microchip PIC32 RNG Driver");
152