1 /*
2  * Nomadik RNG support
3  *  Copyright 2009 Alessandro Rubini
4  *
5  *  This program is free software; you can redistribute it and/or modify
6  *  it under the terms of the GNU General Public License as published by
7  *  the Free Software Foundation; either version 2 of the License, or
8  *  (at your option) any later version.
9  */
10 
11 #include <linux/kernel.h>
12 #include <linux/module.h>
13 #include <linux/init.h>
14 #include <linux/device.h>
15 #include <linux/amba/bus.h>
16 #include <linux/hw_random.h>
17 #include <linux/io.h>
18 #include <linux/clk.h>
19 #include <linux/err.h>
20 
21 static struct clk *rng_clk;
22 
23 static int nmk_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
24 {
25 	void __iomem *base = (void __iomem *)rng->priv;
26 
27 	/*
28 	 * The register is 32 bits and gives 16 random bits (low half).
29 	 * A subsequent read will delay the core for 400ns, so we just read
30 	 * once and accept the very unlikely very small delay, even if wait==0.
31 	 */
32 	*(u16 *)data = __raw_readl(base + 8) & 0xffff;
33 	return 2;
34 }
35 
36 /* we have at most one RNG per machine, granted */
37 static struct hwrng nmk_rng = {
38 	.name		= "nomadik",
39 	.read		= nmk_rng_read,
40 };
41 
42 static int nmk_rng_probe(struct amba_device *dev, const struct amba_id *id)
43 {
44 	void __iomem *base;
45 	int ret;
46 
47 	rng_clk = clk_get(&dev->dev, NULL);
48 	if (IS_ERR(rng_clk)) {
49 		dev_err(&dev->dev, "could not get rng clock\n");
50 		ret = PTR_ERR(rng_clk);
51 		return ret;
52 	}
53 
54 	clk_enable(rng_clk);
55 
56 	ret = amba_request_regions(dev, dev->dev.init_name);
57 	if (ret)
58 		goto out_clk;
59 	ret = -ENOMEM;
60 	base = ioremap(dev->res.start, resource_size(&dev->res));
61 	if (!base)
62 		goto out_release;
63 	nmk_rng.priv = (unsigned long)base;
64 	ret = hwrng_register(&nmk_rng);
65 	if (ret)
66 		goto out_unmap;
67 	return 0;
68 
69 out_unmap:
70 	iounmap(base);
71 out_release:
72 	amba_release_regions(dev);
73 out_clk:
74 	clk_disable(rng_clk);
75 	clk_put(rng_clk);
76 	return ret;
77 }
78 
79 static int nmk_rng_remove(struct amba_device *dev)
80 {
81 	void __iomem *base = (void __iomem *)nmk_rng.priv;
82 	hwrng_unregister(&nmk_rng);
83 	iounmap(base);
84 	amba_release_regions(dev);
85 	clk_disable(rng_clk);
86 	clk_put(rng_clk);
87 	return 0;
88 }
89 
90 static struct amba_id nmk_rng_ids[] = {
91 	{
92 		.id	= 0x000805e1,
93 		.mask	= 0x000fffff, /* top bits are rev and cfg: accept all */
94 	},
95 	{0, 0},
96 };
97 
98 static struct amba_driver nmk_rng_driver = {
99 	.drv = {
100 		.owner = THIS_MODULE,
101 		.name = "rng",
102 		},
103 	.probe = nmk_rng_probe,
104 	.remove = nmk_rng_remove,
105 	.id_table = nmk_rng_ids,
106 };
107 
108 static int __init nmk_rng_init(void)
109 {
110 	return amba_driver_register(&nmk_rng_driver);
111 }
112 
113 static void __devexit nmk_rng_exit(void)
114 {
115 	amba_driver_unregister(&nmk_rng_driver);
116 }
117 
118 module_init(nmk_rng_init);
119 module_exit(nmk_rng_exit);
120 
121 MODULE_LICENSE("GPL");
122