blob: 758de0e9b2ddcf9129ffd61406064c8d850e4596 [file] [log] [blame]
// SPDX-License-Identifier: GPL-2.0-only
/*
* Framework for buffer objects that can be shared across devices/subsystems.
*
* Copyright(C) 2011 Linaro Limited. All rights reserved.
* Author: Sumit Semwal <sumit.semwal@ti.com>
*
* Many thanks to linaro-mm-sig list, and specially
* Arnd Bergmann <arnd@arndb.de>, Rob Clark <rob@ti.com> and
* Daniel Vetter <daniel@ffwll.ch> for their support in creation and
* refining of this idea.
*/
#include <linux/fs.h>
#include <linux/slab.h>
#include <linux/dma-buf.h>
#include <linux/dma-fence.h>
#include <linux/anon_inodes.h>
#include <linux/export.h>
#include <linux/debugfs.h>
#include <linux/module.h>
#include <linux/seq_file.h>
#include <linux/poll.h>
#include <linux/dma-resv.h>
#include <linux/mm.h>
#include <linux/mount.h>
#include <linux/pseudo_fs.h>
#include <uapi/linux/dma-buf.h>
#include <uapi/linux/magic.h>
static inline int is_dma_buf_file(struct file *);
struct dma_buf_list {
struct list_head head;
struct mutex lock;
};
static struct dma_buf_list db_list;
static char *dmabuffs_dname(struct dentry *dentry, char *buffer, int buflen)
{
struct dma_buf *dmabuf;
char name[DMA_BUF_NAME_LEN];
size_t ret = 0;
dmabuf = dentry->d_fsdata;
spin_lock(&dmabuf->name_lock);
if (dmabuf->name)
ret = strlcpy(name, dmabuf->name, DMA_BUF_NAME_LEN);
spin_unlock(&dmabuf->name_lock);
return dynamic_dname(dentry, buffer, buflen, "/%s:%s",
dentry->d_name.name, ret > 0 ? name : "");
}
static void dma_buf_release(struct dentry *dentry)
{
struct dma_buf *dmabuf;
dmabuf = dentry->d_fsdata;
if (unlikely(!dmabuf))
return;
BUG_ON(dmabuf->vmapping_counter);
/*
* Any fences that a dma-buf poll can wait on should be signaled
* before releasing dma-buf. This is the responsibility of each
* driver that uses the reservation objects.
*
* If you hit this BUG() it means someone dropped their ref to the
* dma-buf while still having pending operation to the buffer.
*/
BUG_ON(dmabuf->cb_shared.active || dmabuf->cb_excl.active);
dmabuf->ops->release(dmabuf);
if (dmabuf->resv == (struct dma_resv *)&dmabuf[1])
dma_resv_fini(dmabuf->resv);
module_put(dmabuf->owner);
kfree(dmabuf->name);
kfree(dmabuf);
}
static int dma_buf_file_release(struct inode *inode, struct file *file)
{
struct dma_buf *dmabuf;
if (!is_dma_buf_file(file))
return -EINVAL;
dmabuf = file->private_data;
mutex_lock(&db_list.lock);
list_del(&dmabuf->list_node);
mutex_unlock(&db_list.lock);
return 0;
}
static const struct dentry_operations dma_buf_dentry_ops = {
.d_dname = dmabuffs_dname,
.d_release = dma_buf_release,
};
static struct vfsmount *dma_buf_mnt;
static int dma_buf_fs_init_context(struct fs_context *fc)
{
struct pseudo_fs_context *ctx;
ctx = init_pseudo(fc, DMA_BUF_MAGIC);
if (!ctx)
return -ENOMEM;
ctx->dops = &dma_buf_dentry_ops;
return 0;
}
static struct file_system_type dma_buf_fs_type = {
.name = "dmabuf",
.init_fs_context = dma_buf_fs_init_context,
.kill_sb = kill_anon_super,
};
static int dma_buf_mmap_internal(struct file *file, struct vm_area_struct *vma)
{
struct dma_buf *dmabuf;
if (!is_dma_buf_file(file))
return -EINVAL;
dmabuf = file->private_data;
/* check if buffer supports mmap */
if (!dmabuf->ops->mmap)
return -EINVAL;
/* check for overflowing the buffer's size */
if (vma->vm_pgoff + vma_pages(vma) >
dmabuf->size >> PAGE_SHIFT)
return -EINVAL;
return dmabuf->ops->mmap(dmabuf, vma);
}
static loff_t dma_buf_llseek(struct file *file, loff_t offset, int whence)
{
struct dma_buf *dmabuf;
loff_t base;
if (!is_dma_buf_file(file))
return -EBADF;
dmabuf = file->private_data;
/* only support discovering the end of the buffer,
but also allow SEEK_SET to maintain the idiomatic
SEEK_END(0), SEEK_CUR(0) pattern */
if (whence == SEEK_END)
base = dmabuf->size;
else if (whence == SEEK_SET)
base = 0;
else
return -EINVAL;
if (offset != 0)
return -EINVAL;
return base + offset;
}
/**
* DOC: fence polling
*
* To support cross-device and cross-driver synchronization of buffer access
* implicit fences (represented internally in the kernel with &struct fence) can
* be attached to a &dma_buf. The glue for that and a few related things are
* provided in the &dma_resv structure.
*
* Userspace can query the state of these implicitly tracked fences using poll()
* and related system calls:
*
* - Checking for EPOLLIN, i.e. read access, can be use to query the state of the
* most recent write or exclusive fence.
*
* - Checking for EPOLLOUT, i.e. write access, can be used to query the state of
* all attached fences, shared and exclusive ones.
*
* Note that this only signals the completion of the respective fences, i.e. the
* DMA transfers are complete. Cache flushing and any other necessary
* preparations before CPU access can begin still need to happen.
*/
static void dma_buf_poll_cb(struct dma_fence *fence, struct dma_fence_cb *cb)
{
struct dma_buf_poll_cb_t *dcb = (struct dma_buf_poll_cb_t *)cb;
unsigned long flags;
spin_lock_irqsave(&dcb->poll->lock, flags);
wake_up_locked_poll(dcb->poll, dcb->active);
dcb->active = 0;
spin_unlock_irqrestore(&dcb->poll->lock, flags);
}
static __poll_t dma_buf_poll(struct file *file, poll_table *poll)
{
struct dma_buf *dmabuf;
struct dma_resv *resv;
struct dma_resv_list *fobj;
struct dma_fence *fence_excl;
__poll_t events;
unsigned shared_count, seq;
dmabuf = file->private_data;
if (!dmabuf || !dmabuf->resv)
return EPOLLERR;
resv = dmabuf->resv;
poll_wait(file, &dmabuf->poll, poll);
events = poll_requested_events(poll) & (EPOLLIN | EPOLLOUT);
if (!events)
return 0;
retry:
seq = read_seqcount_begin(&resv->seq);
rcu_read_lock();
fobj = rcu_dereference(resv->fence);
if (fobj)
shared_count = fobj->shared_count;
else
shared_count = 0;
fence_excl = rcu_dereference(resv->fence_excl);
if (read_seqcount_retry(&resv->seq, seq)) {
rcu_read_unlock();
goto retry;
}
if (fence_excl && (!(events & EPOLLOUT) || shared_count == 0)) {
struct dma_buf_poll_cb_t *dcb = &dmabuf->cb_excl;
__poll_t pevents = EPOLLIN;
if (shared_count == 0)
pevents |= EPOLLOUT;
spin_lock_irq(&dmabuf->poll.lock);
if (dcb->active) {
dcb->active |= pevents;
events &= ~pevents;
} else
dcb->active = pevents;
spin_unlock_irq(&dmabuf->poll.lock);
if (events & pevents) {
if (!dma_fence_get_rcu(fence_excl)) {
/* force a recheck */
events &= ~pevents;
dma_buf_poll_cb(NULL, &dcb->cb);
} else if (!dma_fence_add_callback(fence_excl, &dcb->cb,
dma_buf_poll_cb)) {
events &= ~pevents;
dma_fence_put(fence_excl);
} else {
/*
* No callback queued, wake up any additional
* waiters.
*/
dma_fence_put(fence_excl);
dma_buf_poll_cb(NULL, &dcb->cb);
}
}
}
if ((events & EPOLLOUT) && shared_count > 0) {
struct dma_buf_poll_cb_t *dcb = &dmabuf->cb_shared;
int i;
/* Only queue a new callback if no event has fired yet */
spin_lock_irq(&dmabuf->poll.lock);
if (dcb->active)
events &= ~EPOLLOUT;
else
dcb->active = EPOLLOUT;
spin_unlock_irq(&dmabuf->poll.lock);
if (!(events & EPOLLOUT))
goto out;
for (i = 0; i < shared_count; ++i) {
struct dma_fence *fence = rcu_dereference(fobj->shared[i]);
if (!dma_fence_get_rcu(fence)) {
/*
* fence refcount dropped to zero, this means
* that fobj has been freed
*
* call dma_buf_poll_cb and force a recheck!
*/
events &= ~EPOLLOUT;
dma_buf_poll_cb(NULL, &dcb->cb);
break;
}
if (!dma_fence_add_callback(fence, &dcb->cb,
dma_buf_poll_cb)) {
dma_fence_put(fence);
events &= ~EPOLLOUT;
break;
}
dma_fence_put(fence);
}
/* No callback queued, wake up any additional waiters. */
if (i == shared_count)
dma_buf_poll_cb(NULL, &dcb->cb);
}
out:
rcu_read_unlock();
return events;
}
/**
* dma_buf_set_name - Set a name to a specific dma_buf to track the usage.
* The name of the dma-buf buffer can only be set when the dma-buf is not
* attached to any devices. It could theoritically support changing the
* name of the dma-buf if the same piece of memory is used for multiple
* purpose between different devices.
*
* @dmabuf [in] dmabuf buffer that will be renamed.
* @buf: [in] A piece of userspace memory that contains the name of
* the dma-buf.
*
* Returns 0 on success. If the dma-buf buffer is already attached to
* devices, return -EBUSY.
*
*/
static long dma_buf_set_name(struct dma_buf *dmabuf, const char __user *buf)
{
char *name = strndup_user(buf, DMA_BUF_NAME_LEN);
long ret = 0;
if (IS_ERR(name))
return PTR_ERR(name);
mutex_lock(&dmabuf->lock);
if (!list_empty(&dmabuf->attachments)) {
ret = -EBUSY;
kfree(name);
goto out_unlock;
}
spin_lock(&dmabuf->name_lock);
kfree(dmabuf->name);
dmabuf->name = name;
spin_unlock(&dmabuf->name_lock);
out_unlock:
mutex_unlock(&dmabuf->lock);
return ret;
}
static long dma_buf_ioctl(struct file *file,
unsigned int cmd, unsigned long arg)
{
struct dma_buf *dmabuf;
struct dma_buf_sync sync;
enum dma_data_direction direction;
int ret;
dmabuf = file->private_data;
switch (cmd) {
case DMA_BUF_IOCTL_SYNC:
if (copy_from_user(&sync, (void __user *) arg, sizeof(sync)))
return -EFAULT;
if (sync.flags & ~DMA_BUF_SYNC_VALID_FLAGS_MASK)
return -EINVAL;
switch (sync.flags & DMA_BUF_SYNC_RW) {
case DMA_BUF_SYNC_READ:
direction = DMA_FROM_DEVICE;
break;
case DMA_BUF_SYNC_WRITE:
direction = DMA_TO_DEVICE;
break;
case DMA_BUF_SYNC_RW:
direction = DMA_BIDIRECTIONAL;
break;
default:
return -EINVAL;
}
if (sync.flags & DMA_BUF_SYNC_END)
ret = dma_buf_end_cpu_access(dmabuf, direction);
else
ret = dma_buf_begin_cpu_access(dmabuf, direction);
return ret;
case DMA_BUF_SET_NAME_A:
case DMA_BUF_SET_NAME_B:
return dma_buf_set_name(dmabuf, (const char __user *)arg);
default:
return -ENOTTY;
}
}
static void dma_buf_show_fdinfo(struct seq_file *m, struct file *file)
{
struct dma_buf *dmabuf = file->private_data;
seq_printf(m, "size:\t%zu\n", dmabuf->size);
/* Don't count the temporary reference taken inside procfs seq_show */
seq_printf(m, "count:\t%ld\n", file_count(dmabuf->file) - 1);
seq_printf(m, "exp_name:\t%s\n", dmabuf->exp_name);
spin_lock(&dmabuf->name_lock);
if (dmabuf->name)
seq_printf(m, "name:\t%s\n", dmabuf->name);
spin_unlock(&dmabuf->name_lock);
}
static const struct file_operations dma_buf_fops = {
.release = dma_buf_file_release,
.mmap = dma_buf_mmap_internal,
.llseek = dma_buf_llseek,
.poll = dma_buf_poll,
.unlocked_ioctl = dma_buf_ioctl,
#ifdef CONFIG_COMPAT
.compat_ioctl = dma_buf_ioctl,
#endif
.show_fdinfo = dma_buf_show_fdinfo,
};
/*
* is_dma_buf_file - Check if struct file* is associated with dma_buf
*/
static inline int is_dma_buf_file(struct file *file)
{
return file->f_op == &dma_buf_fops;
}
static struct file *dma_buf_getfile(struct dma_buf *dmabuf, int flags)
{
struct file *file;
struct inode *inode = alloc_anon_inode(dma_buf_mnt->mnt_sb);
if (IS_ERR(inode))
return ERR_CAST(inode);
inode->i_size = dmabuf->size;
inode_set_bytes(inode, dmabuf->size);
file = alloc_file_pseudo(inode, dma_buf_mnt, "dmabuf",
flags, &dma_buf_fops);
if (IS_ERR(file))
goto err_alloc_file;
file->f_flags = flags & (O_ACCMODE | O_NONBLOCK);
file->private_data = dmabuf;
file->f_path.dentry->d_fsdata = dmabuf;
return file;
err_alloc_file:
iput(inode);
return file;
}
/**
* DOC: dma buf device access
*
* For device DMA access to a shared DMA buffer the usual sequence of operations
* is fairly simple:
*
* 1. The exporter defines his exporter instance using
* DEFINE_DMA_BUF_EXPORT_INFO() and calls dma_buf_export() to wrap a private
* buffer object into a &dma_buf. It then exports that &dma_buf to userspace
* as a file descriptor by calling dma_buf_fd().
*
* 2. Userspace passes this file-descriptors to all drivers it wants this buffer
* to share with: First the filedescriptor is converted to a &dma_buf using
* dma_buf_get(). Then the buffer is attached to the device using
* dma_buf_attach().
*
* Up to this stage the exporter is still free to migrate or reallocate the
* backing storage.
*
* 3. Once the buffer is attached to all devices userspace can initiate DMA
* access to the shared buffer. In the kernel this is done by calling
* dma_buf_map_attachment() and dma_buf_unmap_attachment().
*
* 4. Once a driver is done with a shared buffer it needs to call
* dma_buf_detach() (after cleaning up any mappings) and then release the
* reference acquired with dma_buf_get by calling dma_buf_put().
*
* For the detailed semantics exporters are expected to implement see
* &dma_buf_ops.
*/
/**
* dma_buf_export - Creates a new dma_buf, and associates an anon file
* with this buffer, so it can be exported.
* Also connect the allocator specific data and ops to the buffer.
* Additionally, provide a name string for exporter; useful in debugging.
*
* @exp_info: [in] holds all the export related information provided
* by the exporter. see &struct dma_buf_export_info
* for further details.
*
* Returns, on success, a newly created dma_buf object, which wraps the
* supplied private data and operations for dma_buf_ops. On either missing
* ops, or error in allocating struct dma_buf, will return negative error.
*
* For most cases the easiest way to create @exp_info is through the
* %DEFINE_DMA_BUF_EXPORT_INFO macro.
*/
struct dma_buf *dma_buf_export(const struct dma_buf_export_info *exp_info)
{
struct dma_buf *dmabuf;
struct dma_resv *resv = exp_info->resv;
struct file *file;
size_t alloc_size = sizeof(struct dma_buf);
int ret;
if (!exp_info->resv)
alloc_size += sizeof(struct dma_resv);
else
/* prevent &dma_buf[1] == dma_buf->resv */
alloc_size += 1;
if (WARN_ON(!exp_info->priv
|| !exp_info->ops
|| !exp_info->ops->map_dma_buf
|| !exp_info->ops->unmap_dma_buf
|| !exp_info->ops->release)) {
return ERR_PTR(-EINVAL);
}
if (!try_module_get(exp_info->owner))
return ERR_PTR(-ENOENT);
dmabuf = kzalloc(alloc_size, GFP_KERNEL);
if (!dmabuf) {
ret = -ENOMEM;
goto err_module;
}
dmabuf->priv = exp_info->priv;
dmabuf->ops = exp_info->ops;
dmabuf->size = exp_info->size;
dmabuf->exp_name = exp_info->exp_name;
dmabuf->owner = exp_info->owner;
spin_lock_init(&dmabuf->name_lock);
init_waitqueue_head(&dmabuf->poll);
dmabuf->cb_excl.poll = dmabuf->cb_shared.poll = &dmabuf->poll;
dmabuf->cb_excl.active = dmabuf->cb_shared.active = 0;
if (!resv) {
resv = (struct dma_resv *)&dmabuf[1];
dma_resv_init(resv);
}
dmabuf->resv = resv;
file = dma_buf_getfile(dmabuf, exp_info->flags);
if (IS_ERR(file)) {
ret = PTR_ERR(file);
goto err_dmabuf;
}
file->f_mode |= FMODE_LSEEK;
dmabuf->file = file;
mutex_init(&dmabuf->lock);
INIT_LIST_HEAD(&dmabuf->attachments);
mutex_lock(&db_list.lock);
list_add(&dmabuf->list_node, &db_list.head);
mutex_unlock(&db_list.lock);
return dmabuf;
err_dmabuf:
kfree(dmabuf);
err_module:
module_put(exp_info->owner);
return ERR_PTR(ret);
}
EXPORT_SYMBOL_GPL(dma_buf_export);
/**
* dma_buf_fd - returns a file descriptor for the given dma_buf
* @dmabuf: [in] pointer to dma_buf for which fd is required.
* @flags: [in] flags to give to fd
*
* On success, returns an associated 'fd'. Else, returns error.
*/
int dma_buf_fd(struct dma_buf *dmabuf, int flags)
{
int fd;
if (!dmabuf || !dmabuf->file)
return -EINVAL;
fd = get_unused_fd_flags(flags);
if (fd < 0)
return fd;
fd_install(fd, dmabuf->file);
return fd;
}
EXPORT_SYMBOL_GPL(dma_buf_fd);
/**
* dma_buf_get - returns the dma_buf structure related to an fd
* @fd: [in] fd associated with the dma_buf to be returned
*
* On success, returns the dma_buf structure associated with an fd; uses
* file's refcounting done by fget to increase refcount. returns ERR_PTR
* otherwise.
*/
struct dma_buf *dma_buf_get(int fd)
{
struct file *file;
file = fget(fd);
if (!file)
return ERR_PTR(-EBADF);
if (!is_dma_buf_file(file)) {
fput(file);
return ERR_PTR(-EINVAL);
}
return file->private_data;
}
EXPORT_SYMBOL_GPL(dma_buf_get);
/**
* dma_buf_put - decreases refcount of the buffer
* @dmabuf: [in] buffer to reduce refcount of
*
* Uses file's refcounting done implicitly by fput().
*
* If, as a result of this call, the refcount becomes 0, the 'release' file
* operation related to this fd is called. It calls &dma_buf_ops.release vfunc
* in turn, and frees the memory allocated for dmabuf when exported.
*/
void dma_buf_put(struct dma_buf *dmabuf)
{
if (WARN_ON(!dmabuf || !dmabuf->file))
return;
fput(dmabuf->file);
}
EXPORT_SYMBOL_GPL(dma_buf_put);
/**
* dma_buf_attach - Add the device to dma_buf's attachments list; optionally,
* calls attach() of dma_buf_ops to allow device-specific attach functionality
* @dmabuf: [in] buffer to attach device to.
* @dev: [in] device to be attached.
*
* Returns struct dma_buf_attachment pointer for this attachment. Attachments
* must be cleaned up by calling dma_buf_detach().
*
* Returns:
*
* A pointer to newly created &dma_buf_attachment on success, or a negative
* error code wrapped into a pointer on failure.
*
* Note that this can fail if the backing storage of @dmabuf is in a place not
* accessible to @dev, and cannot be moved to a more suitable place. This is
* indicated with the error code -EBUSY.
*/
struct dma_buf_attachment *dma_buf_attach(struct dma_buf *dmabuf,
struct device *dev)
{
struct dma_buf_attachment *attach;
int ret;
if (WARN_ON(!dmabuf || !dev))
return ERR_PTR(-EINVAL);
attach = kzalloc(sizeof(*attach), GFP_KERNEL);
if (!attach)
return ERR_PTR(-ENOMEM);
attach->dev = dev;
attach->dmabuf = dmabuf;
mutex_lock(&dmabuf->lock);
if (dmabuf->ops->attach) {
ret = dmabuf->ops->attach(dmabuf, attach);
if (ret)
goto err_attach;
}
list_add(&attach->node, &dmabuf->attachments);
mutex_unlock(&dmabuf->lock);
return attach;
err_attach:
kfree(attach);
mutex_unlock(&dmabuf->lock);
return ERR_PTR(ret);
}
EXPORT_SYMBOL_GPL(dma_buf_attach);
/**
* dma_buf_detach - Remove the given attachment from dmabuf's attachments list;
* optionally calls detach() of dma_buf_ops for device-specific detach
* @dmabuf: [in] buffer to detach from.
* @attach: [in] attachment to be detached; is free'd after this call.
*
* Clean up a device attachment obtained by calling dma_buf_attach().
*/
void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach)
{
if (WARN_ON(!dmabuf || !attach))
return;
if (attach->sgt)
dmabuf->ops->unmap_dma_buf(attach, attach->sgt, attach->dir);
mutex_lock(&dmabuf->lock);
list_del(&attach->node);
if (dmabuf->ops->detach)
dmabuf->ops->detach(dmabuf, attach);
mutex_unlock(&dmabuf->lock);
kfree(attach);
}
EXPORT_SYMBOL_GPL(dma_buf_detach);
/**
* dma_buf_map_attachment - Returns the scatterlist table of the attachment;
* mapped into _device_ address space. Is a wrapper for map_dma_buf() of the
* dma_buf_ops.
* @attach: [in] attachment whose scatterlist is to be returned
* @direction: [in] direction of DMA transfer
*
* Returns sg_table containing the scatterlist to be returned; returns ERR_PTR
* on error. May return -EINTR if it is interrupted by a signal.
*
* A mapping must be unmapped by using dma_buf_unmap_attachment(). Note that
* the underlying backing storage is pinned for as long as a mapping exists,
* therefore users/importers should not hold onto a mapping for undue amounts of
* time.
*/
struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
enum dma_data_direction direction)
{
struct sg_table *sg_table;
might_sleep();
if (WARN_ON(!attach || !attach->dmabuf))
return ERR_PTR(-EINVAL);
if (attach->sgt) {
/*
* Two mappings with different directions for the same
* attachment are not allowed.
*/
if (attach->dir != direction &&
attach->dir != DMA_BIDIRECTIONAL)
return ERR_PTR(-EBUSY);
return attach->sgt;
}
sg_table = attach->dmabuf->ops->map_dma_buf(attach, direction);
if (!sg_table)
sg_table = ERR_PTR(-ENOMEM);
if (!IS_ERR(sg_table) && attach->dmabuf->ops->cache_sgt_mapping) {
attach->sgt = sg_table;
attach->dir = direction;
}
return sg_table;
}
EXPORT_SYMBOL_GPL(dma_buf_map_attachment);
/**
* dma_buf_unmap_attachment - unmaps and decreases usecount of the buffer;might
* deallocate the scatterlist associated. Is a wrapper for unmap_dma_buf() of
* dma_buf_ops.
* @attach: [in] attachment to unmap buffer from
* @sg_table: [in] scatterlist info of the buffer to unmap
* @direction: [in] direction of DMA transfer
*
* This unmaps a DMA mapping for @attached obtained by dma_buf_map_attachment().
*/
void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
struct sg_table *sg_table,
enum dma_data_direction direction)
{
might_sleep();
if (WARN_ON(!attach || !attach->dmabuf || !sg_table))
return;
if (attach->sgt == sg_table)
return;
attach->dmabuf->ops->unmap_dma_buf(attach, sg_table, direction);
}
EXPORT_SYMBOL_GPL(dma_buf_unmap_attachment);
/**
* DOC: cpu access
*
* There are mutliple reasons for supporting CPU access to a dma buffer object:
*
* - Fallback operations in the kernel, for example when a device is connected
* over USB and the kernel needs to shuffle the data around first before
* sending it away. Cache coherency is handled by braketing any transactions
* with calls to dma_buf_begin_cpu_access() and dma_buf_end_cpu_access()
* access.
*
* To support dma_buf objects residing in highmem cpu access is page-based
* using an api similar to kmap. Accessing a dma_buf is done in aligned chunks
* of PAGE_SIZE size. Before accessing a chunk it needs to be mapped, which
* returns a pointer in kernel virtual address space. Afterwards the chunk
* needs to be unmapped again. There is no limit on how often a given chunk
* can be mapped and unmapped, i.e. the importer does not need to call
* begin_cpu_access again before mapping the same chunk again.
*
* Interfaces::
* void \*dma_buf_kmap(struct dma_buf \*, unsigned long);
* void dma_buf_kunmap(struct dma_buf \*, unsigned long, void \*);
*
* Implementing the functions is optional for exporters and for importers all
* the restrictions of using kmap apply.
*
* dma_buf kmap calls outside of the range specified in begin_cpu_access are
* undefined. If the range is not PAGE_SIZE aligned, kmap needs to succeed on
* the partial chunks at the beginning and end but may return stale or bogus
* data outside of the range (in these partial chunks).
*
* For some cases the overhead of kmap can be too high, a vmap interface
* is introduced. This interface should be used very carefully, as vmalloc
* space is a limited resources on many architectures.
*
* Interfaces::
* void \*dma_buf_vmap(struct dma_buf \*dmabuf)
* void dma_buf_vunmap(struct dma_buf \*dmabuf, void \*vaddr)
*
* The vmap call can fail if there is no vmap support in the exporter, or if
* it runs out of vmalloc space. Fallback to kmap should be implemented. Note
* that the dma-buf layer keeps a reference count for all vmap access and
* calls down into the exporter's vmap function only when no vmapping exists,
* and only unmaps it once. Protection against concurrent vmap/vunmap calls is
* provided by taking the dma_buf->lock mutex.
*
* - For full compatibility on the importer side with existing userspace
* interfaces, which might already support mmap'ing buffers. This is needed in
* many processing pipelines (e.g. feeding a software rendered image into a
* hardware pipeline, thumbnail creation, snapshots, ...). Also, Android's ION
* framework already supported this and for DMA buffer file descriptors to
* replace ION buffers mmap support was needed.
*
* There is no special interfaces, userspace simply calls mmap on the dma-buf
* fd. But like for CPU access there's a need to braket the actual access,
* which is handled by the ioctl (DMA_BUF_IOCTL_SYNC). Note that
* DMA_BUF_IOCTL_SYNC can fail with -EAGAIN or -EINTR, in which case it must
* be restarted.
*
* Some systems might need some sort of cache coherency management e.g. when
* CPU and GPU domains are being accessed through dma-buf at the same time.
* To circumvent this problem there are begin/end coherency markers, that
* forward directly to existing dma-buf device drivers vfunc hooks. Userspace
* can make use of those markers through the DMA_BUF_IOCTL_SYNC ioctl. The
* sequence would be used like following:
*
* - mmap dma-buf fd
* - for each drawing/upload cycle in CPU 1. SYNC_START ioctl, 2. read/write
* to mmap area 3. SYNC_END ioctl. This can be repeated as often as you
* want (with the new data being consumed by say the GPU or the scanout
* device)
* - munmap once you don't need the buffer any more
*
* For correctness and optimal performance, it is always required to use
* SYNC_START and SYNC_END before and after, respectively, when accessing the
* mapped address. Userspace cannot rely on coherent access, even when there
* are systems where it just works without calling these ioctls.
*
* - And as a CPU fallback in userspace processing pipelines.
*
* Similar to the motivation for kernel cpu access it is again important that
* the userspace code of a given importing subsystem can use the same
* interfaces with a imported dma-buf buffer object as with a native buffer
* object. This is especially important for drm where the userspace part of
* contemporary OpenGL, X, and other drivers is huge, and reworking them to
* use a different way to mmap a buffer rather invasive.
*
* The assumption in the current dma-buf interfaces is that redirecting the
* initial mmap is all that's needed. A survey of some of the existing
* subsystems shows that no driver seems to do any nefarious thing like
* syncing up with outstanding asynchronous processing on the device or
* allocating special resources at fault time. So hopefully this is good
* enough, since adding interfaces to intercept pagefaults and allow pte
* shootdowns would increase the complexity quite a bit.
*
* Interface::
* int dma_buf_mmap(struct dma_buf \*, struct vm_area_struct \*,
* unsigned long);
*
* If the importing subsystem simply provides a special-purpose mmap call to
* set up a mapping in userspace, calling do_mmap with dma_buf->file will
* equally achieve that for a dma-buf object.
*/
static int __dma_buf_begin_cpu_access(struct dma_buf *dmabuf,
enum dma_data_direction direction)
{
bool write = (direction == DMA_BIDIRECTIONAL ||
direction == DMA_TO_DEVICE);
struct dma_resv *resv = dmabuf->resv;
long ret;
/* Wait on any implicit rendering fences */
ret = dma_resv_wait_timeout_rcu(resv, write, true,
MAX_SCHEDULE_TIMEOUT);
if (ret < 0)
return ret;
return 0;
}
/**
* dma_buf_begin_cpu_access - Must be called before accessing a dma_buf from the
* cpu in the kernel context. Calls begin_cpu_access to allow exporter-specific
* preparations. Coherency is only guaranteed in the specified range for the
* specified access direction.
* @dmabuf: [in] buffer to prepare cpu access for.
* @direction: [in] length of range for cpu access.
*
* After the cpu access is complete the caller should call
* dma_buf_end_cpu_access(). Only when cpu access is braketed by both calls is
* it guaranteed to be coherent with other DMA access.
*
* Can return negative error values, returns 0 on success.
*/
int dma_buf_begin_cpu_access(struct dma_buf *dmabuf,
enum dma_data_direction direction)
{
int ret = 0;
if (WARN_ON(!dmabuf))
return -EINVAL;
if (dmabuf->ops->begin_cpu_access)
ret = dmabuf->ops->begin_cpu_access(dmabuf, direction);
/* Ensure that all fences are waited upon - but we first allow
* the native handler the chance to do so more efficiently if it
* chooses. A double invocation here will be reasonably cheap no-op.
*/
if (ret == 0)
ret = __dma_buf_begin_cpu_access(dmabuf, direction);
return ret;
}
EXPORT_SYMBOL_GPL(dma_buf_begin_cpu_access);
/**
* dma_buf_end_cpu_access - Must be called after accessing a dma_buf from the
* cpu in the kernel context. Calls end_cpu_access to allow exporter-specific
* actions. Coherency is only guaranteed in the specified range for the
* specified access direction.
* @dmabuf: [in] buffer to complete cpu access for.
* @direction: [in] length of range for cpu access.
*
* This terminates CPU access started with dma_buf_begin_cpu_access().
*
* Can return negative error values, returns 0 on success.
*/
int dma_buf_end_cpu_access(struct dma_buf *dmabuf,
enum dma_data_direction direction)
{
int ret = 0;
WARN_ON(!dmabuf);
if (dmabuf->ops->end_cpu_access)
ret = dmabuf->ops->end_cpu_access(dmabuf, direction);
return ret;
}
EXPORT_SYMBOL_GPL(dma_buf_end_cpu_access);
/**
* dma_buf_kmap - Map a page of the buffer object into kernel address space. The
* same restrictions as for kmap and friends apply.
* @dmabuf: [in] buffer to map page from.
* @page_num: [in] page in PAGE_SIZE units to map.
*
* This call must always succeed, any necessary preparations that might fail
* need to be done in begin_cpu_access.
*/
void *dma_buf_kmap(struct dma_buf *dmabuf, unsigned long page_num)
{
WARN_ON(!dmabuf);
if (!dmabuf->ops->map)
return NULL;
return dmabuf->ops->map(dmabuf, page_num);
}
EXPORT_SYMBOL_GPL(dma_buf_kmap);
/**
* dma_buf_kunmap - Unmap a page obtained by dma_buf_kmap.
* @dmabuf: [in] buffer to unmap page from.
* @page_num: [in] page in PAGE_SIZE units to unmap.
* @vaddr: [in] kernel space pointer obtained from dma_buf_kmap.
*
* This call must always succeed.
*/
void dma_buf_kunmap(struct dma_buf *dmabuf, unsigned long page_num,
void *vaddr)
{
WARN_ON(!dmabuf);
if (dmabuf->ops->unmap)
dmabuf->ops->unmap(dmabuf, page_num, vaddr);
}
EXPORT_SYMBOL_GPL(dma_buf_kunmap);
/**
* dma_buf_mmap - Setup up a userspace mmap with the given vma
* @dmabuf: [in] buffer that should back the vma
* @vma: [in] vma for the mmap
* @pgoff: [in] offset in pages where this mmap should start within the
* dma-buf buffer.
*
* This function adjusts the passed in vma so that it points at the file of the
* dma_buf operation. It also adjusts the starting pgoff and does bounds
* checking on the size of the vma. Then it calls the exporters mmap function to
* set up the mapping.
*
* Can return negative error values, returns 0 on success.
*/
int dma_buf_mmap(struct dma_buf *dmabuf, struct vm_area_struct *vma,
unsigned long pgoff)
{
struct file *oldfile;
int ret;
if (WARN_ON(!dmabuf || !vma))
return -EINVAL;
/* check if buffer supports mmap */
if (!dmabuf->ops->mmap)
return -EINVAL;
/* check for offset overflow */
if (pgoff + vma_pages(vma) < pgoff)
return -EOVERFLOW;
/* check for overflowing the buffer's size */
if (pgoff + vma_pages(vma) >
dmabuf->size >> PAGE_SHIFT)
return -EINVAL;
/* readjust the vma */
get_file(dmabuf->file);
oldfile = vma->vm_file;
vma->vm_file = dmabuf->file;
vma->vm_pgoff = pgoff;
ret = dmabuf->ops->mmap(dmabuf, vma);
if (ret) {
/* restore old parameters on failure */
vma->vm_file = oldfile;
fput(dmabuf->file);
} else {
if (oldfile)
fput(oldfile);
}
return ret;
}
EXPORT_SYMBOL_GPL(dma_buf_mmap);
/**
* dma_buf_vmap - Create virtual mapping for the buffer object into kernel
* address space. Same restrictions as for vmap and friends apply.
* @dmabuf: [in] buffer to vmap
*
* This call may fail due to lack of virtual mapping address space.
* These calls are optional in drivers. The intended use for them
* is for mapping objects linear in kernel space for high use objects.
* Please attempt to use kmap/kunmap before thinking about these interfaces.
*
* Returns NULL on error.
*/
void *dma_buf_vmap(struct dma_buf *dmabuf)
{
void *ptr;
if (WARN_ON(!dmabuf))
return NULL;
if (!dmabuf->ops->vmap)
return NULL;
mutex_lock(&dmabuf->lock);
if (dmabuf->vmapping_counter) {
dmabuf->vmapping_counter++;
BUG_ON(!dmabuf->vmap_ptr);
ptr = dmabuf->vmap_ptr;
goto out_unlock;
}
BUG_ON(dmabuf->vmap_ptr);
ptr = dmabuf->ops->vmap(dmabuf);
if (WARN_ON_ONCE(IS_ERR(ptr)))
ptr = NULL;
if (!ptr)
goto out_unlock;
dmabuf->vmap_ptr = ptr;
dmabuf->vmapping_counter = 1;
out_unlock:
mutex_unlock(&dmabuf->lock);
return ptr;
}
EXPORT_SYMBOL_GPL(dma_buf_vmap);
/**
* dma_buf_vunmap - Unmap a vmap obtained by dma_buf_vmap.
* @dmabuf: [in] buffer to vunmap
* @vaddr: [in] vmap to vunmap
*/
void dma_buf_vunmap(struct dma_buf *dmabuf, void *vaddr)
{
if (WARN_ON(!dmabuf))
return;
BUG_ON(!dmabuf->vmap_ptr);
BUG_ON(dmabuf->vmapping_counter == 0);
BUG_ON(dmabuf->vmap_ptr != vaddr);
mutex_lock(&dmabuf->lock);
if (--dmabuf->vmapping_counter == 0) {
if (dmabuf->ops->vunmap)
dmabuf->ops->vunmap(dmabuf, vaddr);
dmabuf->vmap_ptr = NULL;
}
mutex_unlock(&dmabuf->lock);
}
EXPORT_SYMBOL_GPL(dma_buf_vunmap);
#ifdef CONFIG_DEBUG_FS
static int dma_buf_debug_show(struct seq_file *s, void *unused)
{
int ret;
struct dma_buf *buf_obj;
struct dma_buf_attachment *attach_obj;
struct dma_resv *robj;
struct dma_resv_list *fobj;
struct dma_fence *fence;
unsigned seq;
int count = 0, attach_count, shared_count, i;
size_t size = 0;
ret = mutex_lock_interruptible(&db_list.lock);
if (ret)
return ret;
seq_puts(s, "\nDma-buf Objects:\n");
seq_printf(s, "%-8s\t%-8s\t%-8s\t%-8s\texp_name\t%-8s\n",
"size", "flags", "mode", "count", "ino");
list_for_each_entry(buf_obj, &db_list.head, list_node) {
ret = mutex_lock_interruptible(&buf_obj->lock);
if (ret) {
seq_puts(s,
"\tERROR locking buffer object: skipping\n");
continue;
}
seq_printf(s, "%08zu\t%08x\t%08x\t%08ld\t%s\t%08lu\t%s\n",
buf_obj->size,
buf_obj->file->f_flags, buf_obj->file->f_mode,
file_count(buf_obj->file),
buf_obj->exp_name,
file_inode(buf_obj->file)->i_ino,
buf_obj->name ?: "");
robj = buf_obj->resv;
while (true) {
seq = read_seqcount_begin(&robj->seq);
rcu_read_lock();
fobj = rcu_dereference(robj->fence);
shared_count = fobj ? fobj->shared_count : 0;
fence = rcu_dereference(robj->fence_excl);
if (!read_seqcount_retry(&robj->seq, seq))
break;
rcu_read_unlock();
}
if (fence)
seq_printf(s, "\tExclusive fence: %s %s %ssignalled\n",
fence->ops->get_driver_name(fence),
fence->ops->get_timeline_name(fence),
dma_fence_is_signaled(fence) ? "" : "un");
for (i = 0; i < shared_count; i++) {
fence = rcu_dereference(fobj->shared[i]);
if (!dma_fence_get_rcu(fence))
continue;
seq_printf(s, "\tShared fence: %s %s %ssignalled\n",
fence->ops->get_driver_name(fence),
fence->ops->get_timeline_name(fence),
dma_fence_is_signaled(fence) ? "" : "un");
dma_fence_put(fence);
}
rcu_read_unlock();
seq_puts(s, "\tAttached Devices:\n");
attach_count = 0;
list_for_each_entry(attach_obj, &buf_obj->attachments, node) {
seq_printf(s, "\t%s\n", dev_name(attach_obj->dev));
attach_count++;
}
seq_printf(s, "Total %d devices attached\n\n",
attach_count);
count++;
size += buf_obj->size;
mutex_unlock(&buf_obj->lock);
}
seq_printf(s, "\nTotal %d objects, %zu bytes\n", count, size);
mutex_unlock(&db_list.lock);
return 0;
}
DEFINE_SHOW_ATTRIBUTE(dma_buf_debug);
static struct dentry *dma_buf_debugfs_dir;
static int dma_buf_init_debugfs(void)
{
struct dentry *d;
int err = 0;
d = debugfs_create_dir("dma_buf", NULL);
if (IS_ERR(d))
return PTR_ERR(d);
dma_buf_debugfs_dir = d;
d = debugfs_create_file("bufinfo", S_IRUGO, dma_buf_debugfs_dir,
NULL, &dma_buf_debug_fops);
if (IS_ERR(d)) {
pr_debug("dma_buf: debugfs: failed to create node bufinfo\n");
debugfs_remove_recursive(dma_buf_debugfs_dir);
dma_buf_debugfs_dir = NULL;
err = PTR_ERR(d);
}
return err;
}
static void dma_buf_uninit_debugfs(void)
{
debugfs_remove_recursive(dma_buf_debugfs_dir);
}
#else
static inline int dma_buf_init_debugfs(void)
{
return 0;
}
static inline void dma_buf_uninit_debugfs(void)
{
}
#endif
static int __init dma_buf_init(void)
{
dma_buf_mnt = kern_mount(&dma_buf_fs_type);
if (IS_ERR(dma_buf_mnt))
return PTR_ERR(dma_buf_mnt);
mutex_init(&db_list.lock);
INIT_LIST_HEAD(&db_list.head);
dma_buf_init_debugfs();
return 0;
}
subsys_initcall(dma_buf_init);
static void __exit dma_buf_deinit(void)
{
dma_buf_uninit_debugfs();
kern_unmount(dma_buf_mnt);
}
__exitcall(dma_buf_deinit);