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// SPDX-License-Identifier: GPL-2.0-or-later
/* IBM POWER Barrier Synchronization Register Driver
* Copyright IBM Corporation 2008
* Author: Sonny Rao <>
#include <linux/kernel.h>
#include <linux/of.h>
#include <linux/of_address.h>
#include <linux/of_device.h>
#include <linux/of_platform.h>
#include <linux/fs.h>
#include <linux/module.h>
#include <linux/cdev.h>
#include <linux/list.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <asm/pgtable.h>
#include <asm/io.h>
This driver exposes a special register which can be used for fast
synchronization across a large SMP machine. The hardware is exposed
as an array of bytes where each process will write to one of the bytes to
indicate it has finished the current stage and this update is broadcast to
all processors without having to bounce a cacheline between them. In
POWER5 and POWER6 there is one of these registers per SMP, but it is
presented in two forms; first, it is given as a whole and then as a number
of smaller registers which alias to parts of the single whole register.
This can potentially allow multiple groups of processes to each have their
own private synchronization device.
Note that this hardware *must* be written to using *only* single byte writes.
It may be read using 1, 2, 4, or 8 byte loads which must be aligned since
this region is treated as cache-inhibited processes should also use a
full sync before and after writing to the BSR to ensure all stores and
the BSR update have made it to all chips in the system
/* This is arbitrary number, up to Power6 it's been 17 or fewer */
#define BSR_MAX_DEVS (32)
struct bsr_dev {
u64 bsr_addr; /* Real address */
u64 bsr_len; /* length of mem region we can map */
unsigned bsr_bytes; /* size of the BSR reg itself */
unsigned bsr_stride; /* interval at which BSR repeats in the page */
unsigned bsr_type; /* maps to enum below */
unsigned bsr_num; /* bsr id number for its type */
int bsr_minor;
struct list_head bsr_list;
dev_t bsr_dev;
struct cdev bsr_cdev;
struct device *bsr_device;
char bsr_name[32];
static unsigned total_bsr_devs;
static struct list_head bsr_devs = LIST_HEAD_INIT(bsr_devs);
static struct class *bsr_class;
static int bsr_major;
enum {
BSR_8 = 0,
BSR_16 = 1,
BSR_64 = 2,
BSR_128 = 3,
BSR_4096 = 4,
BSR_MAX = 6,
static unsigned bsr_types[BSR_MAX];
static ssize_t
bsr_size_show(struct device *dev, struct device_attribute *attr, char *buf)
struct bsr_dev *bsr_dev = dev_get_drvdata(dev);
return sprintf(buf, "%u\n", bsr_dev->bsr_bytes);
static DEVICE_ATTR_RO(bsr_size);
static ssize_t
bsr_stride_show(struct device *dev, struct device_attribute *attr, char *buf)
struct bsr_dev *bsr_dev = dev_get_drvdata(dev);
return sprintf(buf, "%u\n", bsr_dev->bsr_stride);
static DEVICE_ATTR_RO(bsr_stride);
static ssize_t
bsr_length_show(struct device *dev, struct device_attribute *attr, char *buf)
struct bsr_dev *bsr_dev = dev_get_drvdata(dev);
return sprintf(buf, "%llu\n", bsr_dev->bsr_len);
static DEVICE_ATTR_RO(bsr_length);
static struct attribute *bsr_dev_attrs[] = {
static int bsr_mmap(struct file *filp, struct vm_area_struct *vma)
unsigned long size = vma->vm_end - vma->vm_start;
struct bsr_dev *dev = filp->private_data;
int ret;
vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
/* check for the case of a small BSR device and map one 4k page for it*/
if (dev->bsr_len < PAGE_SIZE && size == PAGE_SIZE)
ret = remap_4k_pfn(vma, vma->vm_start, dev->bsr_addr >> 12,
else if (size <= dev->bsr_len)
ret = io_remap_pfn_range(vma, vma->vm_start,
dev->bsr_addr >> PAGE_SHIFT,
size, vma->vm_page_prot);
return -EINVAL;
if (ret)
return -EAGAIN;
return 0;
static int bsr_open(struct inode *inode, struct file *filp)
struct cdev *cdev = inode->i_cdev;
struct bsr_dev *dev = container_of(cdev, struct bsr_dev, bsr_cdev);
filp->private_data = dev;
return 0;
static const struct file_operations bsr_fops = {
.owner = THIS_MODULE,
.mmap = bsr_mmap,
.open = bsr_open,
.llseek = noop_llseek,
static void bsr_cleanup_devs(void)
struct bsr_dev *cur, *n;
list_for_each_entry_safe(cur, n, &bsr_devs, bsr_list) {
if (cur->bsr_device) {
static int bsr_add_node(struct device_node *bn)
int bsr_stride_len, bsr_bytes_len, num_bsr_devs;
const u32 *bsr_stride;
const u32 *bsr_bytes;
unsigned i;
int ret = -ENODEV;
bsr_stride = of_get_property(bn, "ibm,lock-stride", &bsr_stride_len);
bsr_bytes = of_get_property(bn, "ibm,#lock-bytes", &bsr_bytes_len);
if (!bsr_stride || !bsr_bytes ||
(bsr_stride_len != bsr_bytes_len)) {
printk(KERN_ERR "bsr of-node has missing/incorrect property\n");
return ret;
num_bsr_devs = bsr_bytes_len / sizeof(u32);
for (i = 0 ; i < num_bsr_devs; i++) {
struct bsr_dev *cur = kzalloc(sizeof(struct bsr_dev),
struct resource res;
int result;
if (!cur) {
printk(KERN_ERR "Unable to alloc bsr dev\n");
ret = -ENOMEM;
goto out_err;
result = of_address_to_resource(bn, i, &res);
if (result < 0) {
printk(KERN_ERR "bsr of-node has invalid reg property, skipping\n");
cur->bsr_minor = i + total_bsr_devs;
cur->bsr_addr = res.start;
cur->bsr_len = resource_size(&res);
cur->bsr_bytes = bsr_bytes[i];
cur->bsr_stride = bsr_stride[i];
cur->bsr_dev = MKDEV(bsr_major, i + total_bsr_devs);
/* if we have a bsr_len of > 4k and less then PAGE_SIZE (64k pages) */
/* we can only map 4k of it, so only advertise the 4k in sysfs */
if (cur->bsr_len > 4096 && cur->bsr_len < PAGE_SIZE)
cur->bsr_len = 4096;
switch(cur->bsr_bytes) {
case 8:
cur->bsr_type = BSR_8;
case 16:
cur->bsr_type = BSR_16;
case 64:
cur->bsr_type = BSR_64;
case 128:
cur->bsr_type = BSR_128;
case 4096:
cur->bsr_type = BSR_4096;
cur->bsr_type = BSR_UNKNOWN;
cur->bsr_num = bsr_types[cur->bsr_type];
snprintf(cur->bsr_name, 32, "bsr%d_%d",
cur->bsr_bytes, cur->bsr_num);
cdev_init(&cur->bsr_cdev, &bsr_fops);
result = cdev_add(&cur->bsr_cdev, cur->bsr_dev, 1);
if (result) {
goto out_err;
cur->bsr_device = device_create(bsr_class, NULL, cur->bsr_dev,
cur, "%s", cur->bsr_name);
if (IS_ERR(cur->bsr_device)) {
printk(KERN_ERR "device_create failed for %s\n",
goto out_err;
bsr_types[cur->bsr_type] = cur->bsr_num + 1;
list_add_tail(&cur->bsr_list, &bsr_devs);
total_bsr_devs += num_bsr_devs;
return 0;
return ret;
static int bsr_create_devs(struct device_node *bn)
int ret;
while (bn) {
ret = bsr_add_node(bn);
if (ret) {
return ret;
bn = of_find_compatible_node(bn, NULL, "ibm,bsr");
return 0;
static int __init bsr_init(void)
struct device_node *np;
dev_t bsr_dev;
int ret = -ENODEV;
np = of_find_compatible_node(NULL, NULL, "ibm,bsr");
if (!np)
goto out_err;
bsr_class = class_create(THIS_MODULE, "bsr");
if (IS_ERR(bsr_class)) {
printk(KERN_ERR "class_create() failed for bsr_class\n");
ret = PTR_ERR(bsr_class);
goto out_err_1;
bsr_class->dev_groups = bsr_dev_groups;
ret = alloc_chrdev_region(&bsr_dev, 0, BSR_MAX_DEVS, "bsr");
bsr_major = MAJOR(bsr_dev);
if (ret < 0) {
printk(KERN_ERR "alloc_chrdev_region() failed for bsr\n");
goto out_err_2;
ret = bsr_create_devs(np);
if (ret < 0) {
np = NULL;
goto out_err_3;
return 0;
unregister_chrdev_region(bsr_dev, BSR_MAX_DEVS);
return ret;
static void __exit bsr_exit(void)
if (bsr_class)
if (bsr_major)
unregister_chrdev_region(MKDEV(bsr_major, 0), BSR_MAX_DEVS);
MODULE_AUTHOR("Sonny Rao <>");