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/device.h>
14 #include <linux/amba/bus.h>
15 #include <linux/hw_random.h>
16 #include <linux/io.h>
17 #include <linux/clk.h>
18 #include <linux/err.h>
19 
20 static struct clk *rng_clk;
21 
22 static int nmk_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
23 {
24 	void __iomem *base = (void __iomem *)rng->priv;
25 
26 	/*
27 	 * The register is 32 bits and gives 16 random bits (low half).
28 	 * A subsequent read will delay the core for 400ns, so we just read
29 	 * once and accept the very unlikely very small delay, even if wait==0.
30 	 */
31 	*(u16 *)data = __raw_readl(base + 8) & 0xffff;
32 	return 2;
33 }
34 
35 /* we have at most one RNG per machine, granted */
36 static struct hwrng nmk_rng = {
37 	.name		= "nomadik",
38 	.read		= nmk_rng_read,
39 };
40 
41 static int nmk_rng_probe(struct amba_device *dev, const struct amba_id *id)
42 {
43 	void __iomem *base;
44 	int ret;
45 
46 	rng_clk = devm_clk_get(&dev->dev, NULL);
47 	if (IS_ERR(rng_clk)) {
48 		dev_err(&dev->dev, "could not get rng clock\n");
49 		ret = PTR_ERR(rng_clk);
50 		return ret;
51 	}
52 
53 	clk_prepare_enable(rng_clk);
54 
55 	ret = amba_request_regions(dev, dev->dev.init_name);
56 	if (ret)
57 		goto out_clk;
58 	ret = -ENOMEM;
59 	base = devm_ioremap(&dev->dev, dev->res.start,
60 			    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_release;
67 	return 0;
68 
69 out_release:
70 	amba_release_regions(dev);
71 out_clk:
72 	clk_disable(rng_clk);
73 	return ret;
74 }
75 
76 static int nmk_rng_remove(struct amba_device *dev)
77 {
78 	hwrng_unregister(&nmk_rng);
79 	amba_release_regions(dev);
80 	clk_disable(rng_clk);
81 	return 0;
82 }
83 
84 static struct amba_id nmk_rng_ids[] = {
85 	{
86 		.id	= 0x000805e1,
87 		.mask	= 0x000fffff, /* top bits are rev and cfg: accept all */
88 	},
89 	{0, 0},
90 };
91 
92 MODULE_DEVICE_TABLE(amba, nmk_rng_ids);
93 
94 static struct amba_driver nmk_rng_driver = {
95 	.drv = {
96 		.owner = THIS_MODULE,
97 		.name = "rng",
98 		},
99 	.probe = nmk_rng_probe,
100 	.remove = nmk_rng_remove,
101 	.id_table = nmk_rng_ids,
102 };
103 
104 module_amba_driver(nmk_rng_driver);
105 
106 MODULE_LICENSE("GPL");
107