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1 /*
2  * RNG driver for TX4939 Random Number Generators (RNG)
3  *
4  * Copyright (C) 2009 Atsushi Nemoto <anemo@mba.ocn.ne.jp>
5  *
6  * This file is subject to the terms and conditions of the GNU General Public
7  * License.  See the file "COPYING" in the main directory of this archive
8  * for more details.
9  */
10 #include <linux/err.h>
11 #include <linux/module.h>
12 #include <linux/kernel.h>
13 #include <linux/init.h>
14 #include <linux/delay.h>
15 #include <linux/io.h>
16 #include <linux/platform_device.h>
17 #include <linux/hw_random.h>
18 #include <linux/gfp.h>
19 
20 #define TX4939_RNG_RCSR		0x00000000
21 #define TX4939_RNG_ROR(n)	(0x00000018 + (n) * 8)
22 
23 #define TX4939_RNG_RCSR_INTE	0x00000008
24 #define TX4939_RNG_RCSR_RST	0x00000004
25 #define TX4939_RNG_RCSR_FIN	0x00000002
26 #define TX4939_RNG_RCSR_ST	0x00000001
27 
28 struct tx4939_rng {
29 	struct hwrng rng;
30 	void __iomem *base;
31 	u64 databuf[3];
32 	unsigned int data_avail;
33 };
34 
rng_io_start(void)35 static void rng_io_start(void)
36 {
37 #ifndef CONFIG_64BIT
38 	/*
39 	 * readq is reading a 64-bit register using a 64-bit load.  On
40 	 * a 32-bit kernel however interrupts or any other processor
41 	 * exception would clobber the upper 32-bit of the processor
42 	 * register so interrupts need to be disabled.
43 	 */
44 	local_irq_disable();
45 #endif
46 }
47 
rng_io_end(void)48 static void rng_io_end(void)
49 {
50 #ifndef CONFIG_64BIT
51 	local_irq_enable();
52 #endif
53 }
54 
read_rng(void __iomem * base,unsigned int offset)55 static u64 read_rng(void __iomem *base, unsigned int offset)
56 {
57 	return ____raw_readq(base + offset);
58 }
59 
write_rng(u64 val,void __iomem * base,unsigned int offset)60 static void write_rng(u64 val, void __iomem *base, unsigned int offset)
61 {
62 	return ____raw_writeq(val, base + offset);
63 }
64 
tx4939_rng_data_present(struct hwrng * rng,int wait)65 static int tx4939_rng_data_present(struct hwrng *rng, int wait)
66 {
67 	struct tx4939_rng *rngdev = container_of(rng, struct tx4939_rng, rng);
68 	int i;
69 
70 	if (rngdev->data_avail)
71 		return rngdev->data_avail;
72 	for (i = 0; i < 20; i++) {
73 		rng_io_start();
74 		if (!(read_rng(rngdev->base, TX4939_RNG_RCSR)
75 		      & TX4939_RNG_RCSR_ST)) {
76 			rngdev->databuf[0] =
77 				read_rng(rngdev->base, TX4939_RNG_ROR(0));
78 			rngdev->databuf[1] =
79 				read_rng(rngdev->base, TX4939_RNG_ROR(1));
80 			rngdev->databuf[2] =
81 				read_rng(rngdev->base, TX4939_RNG_ROR(2));
82 			rngdev->data_avail =
83 				sizeof(rngdev->databuf) / sizeof(u32);
84 			/* Start RNG */
85 			write_rng(TX4939_RNG_RCSR_ST,
86 				  rngdev->base, TX4939_RNG_RCSR);
87 			wait = 0;
88 		}
89 		rng_io_end();
90 		if (!wait)
91 			break;
92 		/* 90 bus clock cycles by default for generation */
93 		ndelay(90 * 5);
94 	}
95 	return rngdev->data_avail;
96 }
97 
tx4939_rng_data_read(struct hwrng * rng,u32 * buffer)98 static int tx4939_rng_data_read(struct hwrng *rng, u32 *buffer)
99 {
100 	struct tx4939_rng *rngdev = container_of(rng, struct tx4939_rng, rng);
101 
102 	rngdev->data_avail--;
103 	*buffer = *((u32 *)&rngdev->databuf + rngdev->data_avail);
104 	return sizeof(u32);
105 }
106 
tx4939_rng_probe(struct platform_device * dev)107 static int __init tx4939_rng_probe(struct platform_device *dev)
108 {
109 	struct tx4939_rng *rngdev;
110 	struct resource *r;
111 	int i;
112 
113 	r = platform_get_resource(dev, IORESOURCE_MEM, 0);
114 	if (!r)
115 		return -EBUSY;
116 	rngdev = devm_kzalloc(&dev->dev, sizeof(*rngdev), GFP_KERNEL);
117 	if (!rngdev)
118 		return -ENOMEM;
119 	rngdev->base = devm_ioremap_resource(&dev->dev, r);
120 	if (IS_ERR(rngdev->base))
121 		return PTR_ERR(rngdev->base);
122 
123 	rngdev->rng.name = dev_name(&dev->dev);
124 	rngdev->rng.data_present = tx4939_rng_data_present;
125 	rngdev->rng.data_read = tx4939_rng_data_read;
126 
127 	rng_io_start();
128 	/* Reset RNG */
129 	write_rng(TX4939_RNG_RCSR_RST, rngdev->base, TX4939_RNG_RCSR);
130 	write_rng(0, rngdev->base, TX4939_RNG_RCSR);
131 	/* Start RNG */
132 	write_rng(TX4939_RNG_RCSR_ST, rngdev->base, TX4939_RNG_RCSR);
133 	rng_io_end();
134 	/*
135 	 * Drop first two results.  From the datasheet:
136 	 * The quality of the random numbers generated immediately
137 	 * after reset can be insufficient.  Therefore, do not use
138 	 * random numbers obtained from the first and second
139 	 * generations; use the ones from the third or subsequent
140 	 * generation.
141 	 */
142 	for (i = 0; i < 2; i++) {
143 		rngdev->data_avail = 0;
144 		if (!tx4939_rng_data_present(&rngdev->rng, 1))
145 			return -EIO;
146 	}
147 
148 	platform_set_drvdata(dev, rngdev);
149 	return hwrng_register(&rngdev->rng);
150 }
151 
tx4939_rng_remove(struct platform_device * dev)152 static int __exit tx4939_rng_remove(struct platform_device *dev)
153 {
154 	struct tx4939_rng *rngdev = platform_get_drvdata(dev);
155 
156 	hwrng_unregister(&rngdev->rng);
157 	platform_set_drvdata(dev, NULL);
158 	return 0;
159 }
160 
161 static struct platform_driver tx4939_rng_driver = {
162 	.driver		= {
163 		.name	= "tx4939-rng",
164 		.owner	= THIS_MODULE,
165 	},
166 	.remove = tx4939_rng_remove,
167 };
168 
169 module_platform_driver_probe(tx4939_rng_driver, tx4939_rng_probe);
170 
171 MODULE_DESCRIPTION("H/W Random Number Generator (RNG) driver for TX4939");
172 MODULE_LICENSE("GPL");
173