1 /* 2 * drivers/char/hw_random/timeriomem-rng.c 3 * 4 * Copyright (C) 2009 Alexander Clouter <alex@digriz.org.uk> 5 * 6 * Derived from drivers/char/hw_random/omap-rng.c 7 * Copyright 2005 (c) MontaVista Software, Inc. 8 * Author: Deepak Saxena <dsaxena@plexity.net> 9 * 10 * This program is free software; you can redistribute it and/or modify 11 * it under the terms of the GNU General Public License version 2 as 12 * published by the Free Software Foundation. 13 * 14 * Overview: 15 * This driver is useful for platforms that have an IO range that provides 16 * periodic random data from a single IO memory address. All the platform 17 * has to do is provide the address and 'wait time' that new data becomes 18 * available. 19 * 20 * TODO: add support for reading sizes other than 32bits and masking 21 */ 22 23 #include <linux/completion.h> 24 #include <linux/delay.h> 25 #include <linux/hrtimer.h> 26 #include <linux/hw_random.h> 27 #include <linux/io.h> 28 #include <linux/ktime.h> 29 #include <linux/module.h> 30 #include <linux/of.h> 31 #include <linux/platform_device.h> 32 #include <linux/slab.h> 33 #include <linux/time.h> 34 #include <linux/timeriomem-rng.h> 35 36 struct timeriomem_rng_private { 37 void __iomem *io_base; 38 ktime_t period; 39 unsigned int present:1; 40 41 struct hrtimer timer; 42 struct completion completion; 43 44 struct hwrng rng_ops; 45 }; 46 47 static int timeriomem_rng_read(struct hwrng *hwrng, void *data, 48 size_t max, bool wait) 49 { 50 struct timeriomem_rng_private *priv = 51 container_of(hwrng, struct timeriomem_rng_private, rng_ops); 52 int retval = 0; 53 int period_us = ktime_to_us(priv->period); 54 55 /* 56 * There may not have been enough time for new data to be generated 57 * since the last request. If the caller doesn't want to wait, let them 58 * bail out. Otherwise, wait for the completion. If the new data has 59 * already been generated, the completion should already be available. 60 */ 61 if (!wait && !priv->present) 62 return 0; 63 64 wait_for_completion(&priv->completion); 65 66 do { 67 /* 68 * After the first read, all additional reads will need to wait 69 * for the RNG to generate new data. Since the period can have 70 * a wide range of values (1us to 1s have been observed), allow 71 * for 1% tolerance in the sleep time rather than a fixed value. 72 */ 73 if (retval > 0) 74 usleep_range(period_us, 75 period_us + min(1, period_us / 100)); 76 77 *(u32 *)data = readl(priv->io_base); 78 retval += sizeof(u32); 79 data += sizeof(u32); 80 max -= sizeof(u32); 81 } while (wait && max > sizeof(u32)); 82 83 /* 84 * Block any new callers until the RNG has had time to generate new 85 * data. 86 */ 87 priv->present = 0; 88 reinit_completion(&priv->completion); 89 hrtimer_forward_now(&priv->timer, priv->period); 90 hrtimer_restart(&priv->timer); 91 92 return retval; 93 } 94 95 static enum hrtimer_restart timeriomem_rng_trigger(struct hrtimer *timer) 96 { 97 struct timeriomem_rng_private *priv 98 = container_of(timer, struct timeriomem_rng_private, timer); 99 100 priv->present = 1; 101 complete(&priv->completion); 102 103 return HRTIMER_NORESTART; 104 } 105 106 static int timeriomem_rng_probe(struct platform_device *pdev) 107 { 108 struct timeriomem_rng_data *pdata = pdev->dev.platform_data; 109 struct timeriomem_rng_private *priv; 110 struct resource *res; 111 int err = 0; 112 int period; 113 114 if (!pdev->dev.of_node && !pdata) { 115 dev_err(&pdev->dev, "timeriomem_rng_data is missing\n"); 116 return -EINVAL; 117 } 118 119 res = platform_get_resource(pdev, IORESOURCE_MEM, 0); 120 if (!res) 121 return -ENXIO; 122 123 if (res->start % 4 != 0 || resource_size(res) != 4) { 124 dev_err(&pdev->dev, 125 "address must be four bytes wide and aligned\n"); 126 return -EINVAL; 127 } 128 129 /* Allocate memory for the device structure (and zero it) */ 130 priv = devm_kzalloc(&pdev->dev, 131 sizeof(struct timeriomem_rng_private), GFP_KERNEL); 132 if (!priv) 133 return -ENOMEM; 134 135 platform_set_drvdata(pdev, priv); 136 137 if (pdev->dev.of_node) { 138 int i; 139 140 if (!of_property_read_u32(pdev->dev.of_node, 141 "period", &i)) 142 period = i; 143 else { 144 dev_err(&pdev->dev, "missing period\n"); 145 return -EINVAL; 146 } 147 148 if (!of_property_read_u32(pdev->dev.of_node, 149 "quality", &i)) 150 priv->rng_ops.quality = i; 151 else 152 priv->rng_ops.quality = 0; 153 } else { 154 period = pdata->period; 155 priv->rng_ops.quality = pdata->quality; 156 } 157 158 priv->period = ns_to_ktime(period * NSEC_PER_USEC); 159 init_completion(&priv->completion); 160 hrtimer_init(&priv->timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS); 161 priv->timer.function = timeriomem_rng_trigger; 162 163 priv->rng_ops.name = dev_name(&pdev->dev); 164 priv->rng_ops.read = timeriomem_rng_read; 165 166 priv->io_base = devm_ioremap_resource(&pdev->dev, res); 167 if (IS_ERR(priv->io_base)) { 168 return PTR_ERR(priv->io_base); 169 } 170 171 /* Assume random data is already available. */ 172 priv->present = 1; 173 complete(&priv->completion); 174 175 err = hwrng_register(&priv->rng_ops); 176 if (err) { 177 dev_err(&pdev->dev, "problem registering\n"); 178 return err; 179 } 180 181 dev_info(&pdev->dev, "32bits from 0x%p @ %dus\n", 182 priv->io_base, period); 183 184 return 0; 185 } 186 187 static int timeriomem_rng_remove(struct platform_device *pdev) 188 { 189 struct timeriomem_rng_private *priv = platform_get_drvdata(pdev); 190 191 hwrng_unregister(&priv->rng_ops); 192 hrtimer_cancel(&priv->timer); 193 194 return 0; 195 } 196 197 static const struct of_device_id timeriomem_rng_match[] = { 198 { .compatible = "timeriomem_rng" }, 199 {}, 200 }; 201 MODULE_DEVICE_TABLE(of, timeriomem_rng_match); 202 203 static struct platform_driver timeriomem_rng_driver = { 204 .driver = { 205 .name = "timeriomem_rng", 206 .of_match_table = timeriomem_rng_match, 207 }, 208 .probe = timeriomem_rng_probe, 209 .remove = timeriomem_rng_remove, 210 }; 211 212 module_platform_driver(timeriomem_rng_driver); 213 214 MODULE_LICENSE("GPL"); 215 MODULE_AUTHOR("Alexander Clouter <alex@digriz.org.uk>"); 216 MODULE_DESCRIPTION("Timer IOMEM H/W RNG driver"); 217