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
 28struct tx4939_rng {
 29	struct hwrng rng;
 30	void __iomem *base;
 31	u64 databuf[3];
 32	unsigned int data_avail;
 33};
 34
 35static 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
 48static void rng_io_end(void)
 49{
 50#ifndef CONFIG_64BIT
 51	local_irq_enable();
 52#endif
 53}
 54
 55static u64 read_rng(void __iomem *base, unsigned int offset)
 56{
 57	return ____raw_readq(base + offset);
 58}
 59
 60static void write_rng(u64 val, void __iomem *base, unsigned int offset)
 61{
 62	return ____raw_writeq(val, base + offset);
 63}
 64
 65static 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
 98static 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
107static int __init tx4939_rng_probe(struct platform_device *dev)
108{
109	struct tx4939_rng *rngdev;
110	int i;
111
112	rngdev = devm_kzalloc(&dev->dev, sizeof(*rngdev), GFP_KERNEL);
113	if (!rngdev)
114		return -ENOMEM;
115	rngdev->base = devm_platform_ioremap_resource(dev, 0);
116	if (IS_ERR(rngdev->base))
117		return PTR_ERR(rngdev->base);
118
119	rngdev->rng.name = dev_name(&dev->dev);
120	rngdev->rng.data_present = tx4939_rng_data_present;
121	rngdev->rng.data_read = tx4939_rng_data_read;
122
123	rng_io_start();
124	/* Reset RNG */
125	write_rng(TX4939_RNG_RCSR_RST, rngdev->base, TX4939_RNG_RCSR);
126	write_rng(0, rngdev->base, TX4939_RNG_RCSR);
127	/* Start RNG */
128	write_rng(TX4939_RNG_RCSR_ST, rngdev->base, TX4939_RNG_RCSR);
129	rng_io_end();
130	/*
131	 * Drop first two results.  From the datasheet:
132	 * The quality of the random numbers generated immediately
133	 * after reset can be insufficient.  Therefore, do not use
134	 * random numbers obtained from the first and second
135	 * generations; use the ones from the third or subsequent
136	 * generation.
137	 */
138	for (i = 0; i < 2; i++) {
139		rngdev->data_avail = 0;
140		if (!tx4939_rng_data_present(&rngdev->rng, 1))
141			return -EIO;
142	}
143
144	platform_set_drvdata(dev, rngdev);
145	return devm_hwrng_register(&dev->dev, &rngdev->rng);
146}
147
148static struct platform_driver tx4939_rng_driver = {
149	.driver		= {
150		.name	= "tx4939-rng",
151	},
152};
153
154module_platform_driver_probe(tx4939_rng_driver, tx4939_rng_probe);
155
156MODULE_DESCRIPTION("H/W Random Number Generator (RNG) driver for TX4939");
157MODULE_LICENSE("GPL");