1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * drivers/char/hw_random/timeriomem-rng.c 4 * 5 * Copyright (C) 2009 Alexander Clouter <alex@digriz.org.uk> 6 * 7 * Derived from drivers/char/hw_random/omap-rng.c 8 * Copyright 2005 (c) MontaVista Software, Inc. 9 * Author: Deepak Saxena <dsaxena@plexity.net> 10 * 11 * Overview: 12 * This driver is useful for platforms that have an IO range that provides 13 * periodic random data from a single IO memory address. All the platform 14 * has to do is provide the address and 'wait time' that new data becomes 15 * available. 16 * 17 * TODO: add support for reading sizes other than 32bits and masking 18 */ 19 20 #include <linux/completion.h> 21 #include <linux/delay.h> 22 #include <linux/hrtimer.h> 23 #include <linux/hw_random.h> 24 #include <linux/io.h> 25 #include <linux/ktime.h> 26 #include <linux/module.h> 27 #include <linux/of.h> 28 #include <linux/platform_device.h> 29 #include <linux/slab.h> 30 #include <linux/time.h> 31 #include <linux/timeriomem-rng.h> 32 33 struct timeriomem_rng_private { 34 void __iomem *io_base; 35 ktime_t period; 36 unsigned int present:1; 37 38 struct hrtimer timer; 39 struct completion completion; 40 41 struct hwrng rng_ops; 42 }; 43 44 static int timeriomem_rng_read(struct hwrng *hwrng, void *data, 45 size_t max, bool wait) 46 { 47 struct timeriomem_rng_private *priv = 48 container_of(hwrng, struct timeriomem_rng_private, rng_ops); 49 int retval = 0; 50 int period_us = ktime_to_us(priv->period); 51 52 /* 53 * There may not have been enough time for new data to be generated 54 * since the last request. If the caller doesn't want to wait, let them 55 * bail out. Otherwise, wait for the completion. If the new data has 56 * already been generated, the completion should already be available. 57 */ 58 if (!wait && !priv->present) 59 return 0; 60 61 wait_for_completion(&priv->completion); 62 63 do { 64 /* 65 * After the first read, all additional reads will need to wait 66 * for the RNG to generate new data. Since the period can have 67 * a wide range of values (1us to 1s have been observed), allow 68 * for 1% tolerance in the sleep time rather than a fixed value. 69 */ 70 if (retval > 0) 71 usleep_range(period_us, 72 period_us + max(1, period_us / 100)); 73 74 *(u32 *)data = readl(priv->io_base); 75 retval += sizeof(u32); 76 data += sizeof(u32); 77 max -= sizeof(u32); 78 } while (wait && max > sizeof(u32)); 79 80 /* 81 * Block any new callers until the RNG has had time to generate new 82 * data. 83 */ 84 priv->present = 0; 85 reinit_completion(&priv->completion); 86 hrtimer_forward_now(&priv->timer, priv->period); 87 hrtimer_restart(&priv->timer); 88 89 return retval; 90 } 91 92 static enum hrtimer_restart timeriomem_rng_trigger(struct hrtimer *timer) 93 { 94 struct timeriomem_rng_private *priv 95 = container_of(timer, struct timeriomem_rng_private, timer); 96 97 priv->present = 1; 98 complete(&priv->completion); 99 100 return HRTIMER_NORESTART; 101 } 102 103 static int timeriomem_rng_probe(struct platform_device *pdev) 104 { 105 struct timeriomem_rng_data *pdata = pdev->dev.platform_data; 106 struct timeriomem_rng_private *priv; 107 struct resource *res; 108 int err = 0; 109 int period; 110 111 if (!pdev->dev.of_node && !pdata) { 112 dev_err(&pdev->dev, "timeriomem_rng_data is missing\n"); 113 return -EINVAL; 114 } 115 116 /* Allocate memory for the device structure (and zero it) */ 117 priv = devm_kzalloc(&pdev->dev, 118 sizeof(struct timeriomem_rng_private), GFP_KERNEL); 119 if (!priv) 120 return -ENOMEM; 121 122 platform_set_drvdata(pdev, priv); 123 124 priv->io_base = devm_platform_get_and_ioremap_resource(pdev, 0, &res); 125 if (IS_ERR(priv->io_base)) 126 return PTR_ERR(priv->io_base); 127 128 if (res->start % 4 != 0 || resource_size(res) < 4) { 129 dev_err(&pdev->dev, 130 "address must be at least four bytes wide and 32-bit aligned\n"); 131 return -EINVAL; 132 } 133 134 if (pdev->dev.of_node) { 135 int i; 136 137 if (!of_property_read_u32(pdev->dev.of_node, 138 "period", &i)) 139 period = i; 140 else { 141 dev_err(&pdev->dev, "missing period\n"); 142 return -EINVAL; 143 } 144 145 if (!of_property_read_u32(pdev->dev.of_node, 146 "quality", &i)) 147 priv->rng_ops.quality = i; 148 } else { 149 period = pdata->period; 150 priv->rng_ops.quality = pdata->quality; 151 } 152 153 priv->period = ns_to_ktime(period * NSEC_PER_USEC); 154 init_completion(&priv->completion); 155 hrtimer_init(&priv->timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS); 156 priv->timer.function = timeriomem_rng_trigger; 157 158 priv->rng_ops.name = dev_name(&pdev->dev); 159 priv->rng_ops.read = timeriomem_rng_read; 160 161 /* Assume random data is already available. */ 162 priv->present = 1; 163 complete(&priv->completion); 164 165 err = devm_hwrng_register(&pdev->dev, &priv->rng_ops); 166 if (err) { 167 dev_err(&pdev->dev, "problem registering\n"); 168 return err; 169 } 170 171 dev_info(&pdev->dev, "32bits from 0x%p @ %dus\n", 172 priv->io_base, period); 173 174 return 0; 175 } 176 177 static int timeriomem_rng_remove(struct platform_device *pdev) 178 { 179 struct timeriomem_rng_private *priv = platform_get_drvdata(pdev); 180 181 hrtimer_cancel(&priv->timer); 182 183 return 0; 184 } 185 186 static const struct of_device_id timeriomem_rng_match[] = { 187 { .compatible = "timeriomem_rng" }, 188 {}, 189 }; 190 MODULE_DEVICE_TABLE(of, timeriomem_rng_match); 191 192 static struct platform_driver timeriomem_rng_driver = { 193 .driver = { 194 .name = "timeriomem_rng", 195 .of_match_table = timeriomem_rng_match, 196 }, 197 .probe = timeriomem_rng_probe, 198 .remove = timeriomem_rng_remove, 199 }; 200 201 module_platform_driver(timeriomem_rng_driver); 202 203 MODULE_LICENSE("GPL"); 204 MODULE_AUTHOR("Alexander Clouter <alex@digriz.org.uk>"); 205 MODULE_DESCRIPTION("Timer IOMEM H/W RNG driver"); 206