// SPDX-License-Identifier: GPL-2.0-only
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/*
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* s390 TRNG device driver
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*
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* Driver for the TRNG (true random number generation) command
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* available via CPACF extension MSA 7 on the s390 arch.
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* Copyright IBM Corp. 2017
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* Author(s): Harald Freudenberger <freude@de.ibm.com>
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*/
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#define KMSG_COMPONENT "trng"
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#define pr_fmt(fmt) KMSG_COMPONENT ": " fmt
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#include <linux/hw_random.h>
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/cpufeature.h>
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#include <linux/miscdevice.h>
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#include <linux/debugfs.h>
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#include <linux/atomic.h>
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#include <linux/random.h>
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#include <linux/sched/signal.h>
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#include <asm/debug.h>
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#include <asm/cpacf.h>
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MODULE_LICENSE("GPL v2");
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MODULE_AUTHOR("IBM Corporation");
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MODULE_DESCRIPTION("s390 CPACF TRNG device driver");
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/* trng related debug feature things */
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static debug_info_t *debug_info;
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#define DEBUG_DBG(...) debug_sprintf_event(debug_info, 6, ##__VA_ARGS__)
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#define DEBUG_INFO(...) debug_sprintf_event(debug_info, 5, ##__VA_ARGS__)
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#define DEBUG_WARN(...) debug_sprintf_event(debug_info, 4, ##__VA_ARGS__)
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#define DEBUG_ERR(...) debug_sprintf_event(debug_info, 3, ##__VA_ARGS__)
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/* trng helpers */
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static atomic64_t trng_dev_counter = ATOMIC64_INIT(0);
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static atomic64_t trng_hwrng_counter = ATOMIC64_INIT(0);
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/* file io functions */
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static int trng_open(struct inode *inode, struct file *file)
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{
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return nonseekable_open(inode, file);
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}
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static ssize_t trng_read(struct file *file, char __user *ubuf,
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size_t nbytes, loff_t *ppos)
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{
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u8 buf[32];
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u8 *p = buf;
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unsigned int n;
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ssize_t ret = 0;
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/*
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* use buf for requests <= sizeof(buf),
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* otherwise allocate one page and fetch
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* pagewise.
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*/
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if (nbytes > sizeof(buf)) {
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p = (u8 *) __get_free_page(GFP_KERNEL);
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if (!p)
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return -ENOMEM;
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}
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while (nbytes) {
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if (need_resched()) {
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if (signal_pending(current)) {
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if (ret == 0)
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ret = -ERESTARTSYS;
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break;
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}
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schedule();
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}
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n = nbytes > PAGE_SIZE ? PAGE_SIZE : nbytes;
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cpacf_trng(NULL, 0, p, n);
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atomic64_add(n, &trng_dev_counter);
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if (copy_to_user(ubuf, p, n)) {
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ret = -EFAULT;
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break;
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}
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nbytes -= n;
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ubuf += n;
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ret += n;
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}
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if (p != buf)
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free_page((unsigned long) p);
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DEBUG_DBG("trng_read()=%zd\n", ret);
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return ret;
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}
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/* sysfs */
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static ssize_t trng_counter_show(struct device *dev,
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struct device_attribute *attr, char *buf)
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{
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u64 dev_counter = atomic64_read(&trng_dev_counter);
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u64 hwrng_counter = atomic64_read(&trng_hwrng_counter);
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#if IS_ENABLED(CONFIG_ARCH_RANDOM)
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u64 arch_counter = atomic64_read(&s390_arch_random_counter);
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return snprintf(buf, PAGE_SIZE,
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"trng: %llu\n"
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"hwrng: %llu\n"
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"arch: %llu\n"
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"total: %llu\n",
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dev_counter, hwrng_counter, arch_counter,
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dev_counter + hwrng_counter + arch_counter);
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#else
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return snprintf(buf, PAGE_SIZE,
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"trng: %llu\n"
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"hwrng: %llu\n"
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"total: %llu\n",
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dev_counter, hwrng_counter,
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dev_counter + hwrng_counter);
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#endif
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}
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static DEVICE_ATTR(byte_counter, 0444, trng_counter_show, NULL);
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static struct attribute *trng_dev_attrs[] = {
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&dev_attr_byte_counter.attr,
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NULL
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};
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static const struct attribute_group trng_dev_attr_group = {
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.attrs = trng_dev_attrs
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};
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static const struct attribute_group *trng_dev_attr_groups[] = {
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&trng_dev_attr_group,
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NULL
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};
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static const struct file_operations trng_fops = {
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.owner = THIS_MODULE,
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.open = &trng_open,
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.release = NULL,
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.read = &trng_read,
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.llseek = noop_llseek,
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};
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static struct miscdevice trng_dev = {
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.name = "trng",
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.minor = MISC_DYNAMIC_MINOR,
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.mode = 0444,
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.fops = &trng_fops,
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.groups = trng_dev_attr_groups,
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};
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/* hwrng_register */
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static inline void _trng_hwrng_read(u8 *buf, size_t len)
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{
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cpacf_trng(NULL, 0, buf, len);
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atomic64_add(len, &trng_hwrng_counter);
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}
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static int trng_hwrng_data_read(struct hwrng *rng, u32 *data)
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{
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size_t len = sizeof(*data);
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_trng_hwrng_read((u8 *) data, len);
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DEBUG_DBG("trng_hwrng_data_read()=%zu\n", len);
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return len;
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}
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static int trng_hwrng_read(struct hwrng *rng, void *data, size_t max, bool wait)
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{
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size_t len = max <= PAGE_SIZE ? max : PAGE_SIZE;
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_trng_hwrng_read((u8 *) data, len);
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DEBUG_DBG("trng_hwrng_read()=%zu\n", len);
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return len;
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}
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/*
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* hwrng register struct
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* The trng is suppost to have 100% entropy, and thus
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* we register with a very high quality value.
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*/
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static struct hwrng trng_hwrng_dev = {
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.name = "s390-trng",
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.data_read = trng_hwrng_data_read,
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.read = trng_hwrng_read,
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.quality = 999,
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};
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/* init and exit */
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static void __init trng_debug_init(void)
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{
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debug_info = debug_register("trng", 1, 1, 4 * sizeof(long));
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debug_register_view(debug_info, &debug_sprintf_view);
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debug_set_level(debug_info, 3);
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}
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static void trng_debug_exit(void)
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{
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debug_unregister(debug_info);
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}
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static int __init trng_init(void)
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{
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int ret;
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trng_debug_init();
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/* check if subfunction CPACF_PRNO_TRNG is available */
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if (!cpacf_query_func(CPACF_PRNO, CPACF_PRNO_TRNG)) {
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DEBUG_INFO("trng_init CPACF_PRNO_TRNG not available\n");
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ret = -ENODEV;
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goto out_dbg;
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}
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ret = misc_register(&trng_dev);
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if (ret) {
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DEBUG_WARN("trng_init misc_register() failed rc=%d\n", ret);
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goto out_dbg;
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}
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ret = hwrng_register(&trng_hwrng_dev);
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if (ret) {
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DEBUG_WARN("trng_init hwrng_register() failed rc=%d\n", ret);
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goto out_misc;
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}
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DEBUG_DBG("trng_init successful\n");
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return 0;
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out_misc:
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misc_deregister(&trng_dev);
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out_dbg:
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trng_debug_exit();
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return ret;
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}
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static void __exit trng_exit(void)
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{
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hwrng_unregister(&trng_hwrng_dev);
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misc_deregister(&trng_dev);
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trng_debug_exit();
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}
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module_cpu_feature_match(MSA, trng_init);
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module_exit(trng_exit);
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