[PATCH v6 0/4] usb: gadget: functionfs: DMABUF import interface

[PATCH v6 0/4] usb: gadget: functionfs: DMABUF import interface

[Paul Cercueil]

Hi,

This is the v6 of my patchset that adds a new DMABUF import interface to
FunctionFS.

Given that the cache coherency issue that has been discussed after my
v5 is a tangential problem and not directly related to this new
interface, I decided to drop the dma_buf_begin/end_access() functions
for now - but I'm open to the idea of re-introducing them in a
subsequent patchset.

The patchset was rebased on next-20240129.

Cheers,
-Paul

---
Changelog:
* Drop v5's patches [1/6] and [2/6].
* [3/4]: 
  - Drop use of dma_buf_begin/end_access(). We now make the assumption
    that the devices attached to the DMABUFs must be coherent between
    themselves. The cache coherency issue is a tangential problem, and
    those functions can be re-introduced in a subsequent patchset.
  - Unqueue pending requests on detach. Otherwise, when closing the data
    endpoint the DMABUF will never be signaled.
  - Use list_for_each_entry_safe() in ffs_dmabuf_detach(), because there
    is a list_del() in there.
  - use pr_vdebug() instead of pr_debug()
  - Rename ffs_dmabuf_unmap_work() -> ffs_dmabuf_cleanup()

---
Paul Cercueil (4):
  usb: gadget: Support already-mapped DMA SGs
  usb: gadget: functionfs: Factorize wait-for-endpoint code
  usb: gadget: functionfs: Add DMABUF import interface
  Documentation: usb: Document FunctionFS DMABUF API

 Documentation/usb/functionfs.rst    |  36 ++
 drivers/usb/gadget/Kconfig          |   1 +
 drivers/usb/gadget/function/f_fs.c  | 513 ++++++++++++++++++++++++++--
 drivers/usb/gadget/udc/core.c       |   7 +-
 include/linux/usb/gadget.h          |   2 +
 include/uapi/linux/usb/functionfs.h |  41 +++
 6 files changed, 579 insertions(+), 21 deletions(-)

-- 
2.43.0

[PATCH v6 1/4] usb: gadget: Support already-mapped DMA SGs

[Paul Cercueil]

Add a new 'sg_was_mapped' field to the struct usb_request. This field
can be used to indicate that the scatterlist associated to the USB
transfer has already been mapped into the DMA space, and it does not
have to be done internally.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
---
 drivers/usb/gadget/udc/core.c | 7 ++++++-
 include/linux/usb/gadget.h    | 2 ++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/gadget/udc/core.c b/drivers/usb/gadget/udc/core.c
index d59f94464b87..9d4150124fdb 100644
--- a/drivers/usb/gadget/udc/core.c
+++ b/drivers/usb/gadget/udc/core.c
@@ -903,6 +903,11 @@ int usb_gadget_map_request_by_dev(struct device *dev,
 	if (req->length == 0)
 		return 0;
 
+	if (req->sg_was_mapped) {
+		req->num_mapped_sgs = req->num_sgs;
+		return 0;
+	}
+
 	if (req->num_sgs) {
 		int     mapped;
 
@@ -948,7 +953,7 @@ EXPORT_SYMBOL_GPL(usb_gadget_map_request);
 void usb_gadget_unmap_request_by_dev(struct device *dev,
 		struct usb_request *req, int is_in)
 {
-	if (req->length == 0)
+	if (req->length == 0 || req->sg_was_mapped)
 		return;
 
 	if (req->num_mapped_sgs) {
diff --git a/include/linux/usb/gadget.h b/include/linux/usb/gadget.h
index a771ccc038ac..c529e4e06997 100644
--- a/include/linux/usb/gadget.h
+++ b/include/linux/usb/gadget.h
@@ -52,6 +52,7 @@ struct usb_ep;
  * @short_not_ok: When reading data, makes short packets be
  *     treated as errors (queue stops advancing till cleanup).
  * @dma_mapped: Indicates if request has been mapped to DMA (internal)
+ * @sg_was_mapped: Set if the scatterlist has been mapped before the request
  * @complete: Function called when request completes, so this request and
  *	its buffer may be re-used.  The function will always be called with
  *	interrupts disabled, and it must not sleep.
@@ -111,6 +112,7 @@ struct usb_request {
 	unsigned		zero:1;
 	unsigned		short_not_ok:1;
 	unsigned		dma_mapped:1;
+	unsigned		sg_was_mapped:1;
 
 	void			(*complete)(struct usb_ep *ep,
 					struct usb_request *req);
-- 
2.43.0

[PATCH v6 2/4] usb: gadget: functionfs: Factorize wait-for-endpoint code

[Paul Cercueil]

This exact same code was duplicated in two different places.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
---
 drivers/usb/gadget/function/f_fs.c | 48 +++++++++++++++++-------------
 1 file changed, 27 insertions(+), 21 deletions(-)

diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index be3851cffb73..491a1e0f4fa3 100644
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -934,31 +934,44 @@ static ssize_t __ffs_epfile_read_data(struct ffs_epfile *epfile,
 	return ret;
 }
 
-static ssize_t ffs_epfile_io(struct file *file, struct ffs_io_data *io_data)
+static struct ffs_ep *ffs_epfile_wait_ep(struct file *file)
 {
 	struct ffs_epfile *epfile = file->private_data;
-	struct usb_request *req;
 	struct ffs_ep *ep;
-	char *data = NULL;
-	ssize_t ret, data_len = -EINVAL;
-	int halt;
-
-	/* Are we still active? */
-	if (WARN_ON(epfile->ffs->state != FFS_ACTIVE))
-		return -ENODEV;
+	int ret;
 
 	/* Wait for endpoint to be enabled */
 	ep = epfile->ep;
 	if (!ep) {
 		if (file->f_flags & O_NONBLOCK)
-			return -EAGAIN;
+			return ERR_PTR(-EAGAIN);
 
 		ret = wait_event_interruptible(
 				epfile->ffs->wait, (ep = epfile->ep));
 		if (ret)
-			return -EINTR;
+			return ERR_PTR(-EINTR);
 	}
 
+	return ep;
+}
+
+static ssize_t ffs_epfile_io(struct file *file, struct ffs_io_data *io_data)
+{
+	struct ffs_epfile *epfile = file->private_data;
+	struct usb_request *req;
+	struct ffs_ep *ep;
+	char *data = NULL;
+	ssize_t ret, data_len = -EINVAL;
+	int halt;
+
+	/* Are we still active? */
+	if (WARN_ON(epfile->ffs->state != FFS_ACTIVE))
+		return -ENODEV;
+
+	ep = ffs_epfile_wait_ep(file);
+	if (IS_ERR(ep))
+		return PTR_ERR(ep);
+
 	/* Do we halt? */
 	halt = (!io_data->read == !epfile->in);
 	if (halt && epfile->isoc)
@@ -1280,16 +1293,9 @@ static long ffs_epfile_ioctl(struct file *file, unsigned code,
 		return -ENODEV;
 
 	/* Wait for endpoint to be enabled */
-	ep = epfile->ep;
-	if (!ep) {
-		if (file->f_flags & O_NONBLOCK)
-			return -EAGAIN;
-
-		ret = wait_event_interruptible(
-				epfile->ffs->wait, (ep = epfile->ep));
-		if (ret)
-			return -EINTR;
-	}
+	ep = ffs_epfile_wait_ep(file);
+	if (IS_ERR(ep))
+		return PTR_ERR(ep);
 
 	spin_lock_irq(&epfile->ffs->eps_lock);
 
-- 
2.43.0

[PATCH v6 3/4] usb: gadget: functionfs: Add DMABUF import interface

[Paul Cercueil]

This patch introduces three new ioctls. They all should be called on a
data endpoint (ie. not ep0). They are:

- FUNCTIONFS_DMABUF_ATTACH, which takes the file descriptor of a DMABUF
  object to attach to the endpoint.

- FUNCTIONFS_DMABUF_DETACH, which takes the file descriptor of the
  DMABUF to detach from the endpoint. Note that closing the endpoint's
  file descriptor will automatically detach all attached DMABUFs.

- FUNCTIONFS_DMABUF_TRANSFER, which requests a data transfer from / to
  the given DMABUF. Its argument is a structure that packs the DMABUF's
  file descriptor, the size in bytes to transfer (which should generally
  be set to the size of the DMABUF), and a 'flags' field which is unused
  for now.
  Before this ioctl can be used, the related DMABUF must be attached
  with FUNCTIONFS_DMABUF_ATTACH.

These three ioctls enable the FunctionFS code to transfer data between
the USB stack and a DMABUF object, which can be provided by a driver
from a completely different subsystem, in a zero-copy fashion.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Christian König <christian.koenig@amd.com>

---
v2:
- Make ffs_dma_resv_lock() static
- Add MODULE_IMPORT_NS(DMA_BUF);
- The attach/detach functions are now performed without locking the
  eps_lock spinlock. The transfer function starts with the spinlock
  unlocked, then locks it before allocating and queueing the USB
  transfer.

v3:
- Inline to_ffs_dma_fence() which was called only once.
- Simplify ffs_dma_resv_lock()
- Add comment explaining why we unref twice in ffs_dmabuf_detach()
- Document uapi struct usb_ffs_dmabuf_transfer_req and IOCTLs

v4:
- Protect the DMABUF list with a mutex
- Use incremental sequence number for the dma_fences
- Unref attachments and DMABUFs in workers
- Remove dead code in ffs_dma_resv_lock()
- Fix non-block actually blocking
- Use dma_fence_begin/end_signalling()
- Add comment about cache-management and dma_buf_unmap_attachment()
- Make sure dma_buf_map_attachment() is called with the dma-resv locked

v5:
- Cache the dma_buf_attachment while the DMABUF is attached.
- Use dma_buf_begin/end_access() to ensure that the DMABUF data will be
  coherent to the hardware.
- Remove comment about cache-management and dma_buf_unmap_attachment(),
  since we now use dma_buf_begin/end_access().
- Added Christian's ACK
- Select DMA_SHARED_BUFFER in Kconfig entry

v6:
- Drop use of dma_buf_begin/end_access(). We now make the assumption
  that the devices attached to the DMABUFs must be coherent between
  themselves. The cache coherency issue is a tangential problem, and
  those functions can be re-introduced in a subsequent patchset.
- Unqueue pending requests on detach. Otherwise, when closing the data
  endpoint the DMABUF will never be signaled.
- Use list_for_each_entry_safe() in ffs_dmabuf_detach(), because there
  is a list_del() in there.
- Use pr_vdebug() instead of pr_debug()
- Rename ffs_dmabuf_unmap_work() -> ffs_dmabuf_cleanup()
---
 drivers/usb/gadget/Kconfig          |   1 +
 drivers/usb/gadget/function/f_fs.c  | 467 ++++++++++++++++++++++++++++
 include/uapi/linux/usb/functionfs.h |  41 +++
 3 files changed, 509 insertions(+)

diff --git a/drivers/usb/gadget/Kconfig b/drivers/usb/gadget/Kconfig
index b3592bcb0f96..566ff0b1282a 100644
--- a/drivers/usb/gadget/Kconfig
+++ b/drivers/usb/gadget/Kconfig
@@ -190,6 +190,7 @@ config USB_F_MASS_STORAGE
 	tristate
 
 config USB_F_FS
+	select DMA_SHARED_BUFFER
 	tristate
 
 config USB_F_UAC1
diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
index 491a1e0f4fa3..bffbc1dc651f 100644
--- a/drivers/usb/gadget/function/f_fs.c
+++ b/drivers/usb/gadget/function/f_fs.c
@@ -15,6 +15,9 @@
 /* #define VERBOSE_DEBUG */
 
 #include <linux/blkdev.h>
+#include <linux/dma-buf.h>
+#include <linux/dma-fence.h>
+#include <linux/dma-resv.h>
 #include <linux/pagemap.h>
 #include <linux/export.h>
 #include <linux/fs_parser.h>
@@ -43,6 +46,8 @@
 
 #define FUNCTIONFS_MAGIC	0xa647361 /* Chosen by a honest dice roll ;) */
 
+MODULE_IMPORT_NS(DMA_BUF);
+
 /* Reference counter handling */
 static void ffs_data_get(struct ffs_data *ffs);
 static void ffs_data_put(struct ffs_data *ffs);
@@ -124,6 +129,25 @@ struct ffs_ep {
 	u8				num;
 };
 
+struct ffs_dmabuf_priv {
+	struct list_head entry;
+	struct kref ref;
+	struct ffs_data *ffs;
+	struct dma_buf_attachment *attach;
+	struct sg_table *sgt;
+	enum dma_data_direction dir;
+	spinlock_t lock;
+	u64 context;
+	struct usb_request *req;	/* P: ffs->eps_lock */
+	struct usb_ep *ep;		/* P: ffs->eps_lock */
+};
+
+struct ffs_dma_fence {
+	struct dma_fence base;
+	struct ffs_dmabuf_priv *priv;
+	struct work_struct work;
+};
+
 struct ffs_epfile {
 	/* Protects ep->ep and ep->req. */
 	struct mutex			mutex;
@@ -197,6 +221,11 @@ struct ffs_epfile {
 	unsigned char			isoc;	/* P: ffs->eps_lock */
 
 	unsigned char			_pad;
+
+	/* Protects dmabufs */
+	struct mutex			dmabufs_mutex;
+	struct list_head		dmabufs; /* P: dmabufs_mutex */
+	atomic_t			seqno;
 };
 
 struct ffs_buffer {
@@ -1271,10 +1300,58 @@ static ssize_t ffs_epfile_read_iter(struct kiocb *kiocb, struct iov_iter *to)
 	return res;
 }
 
+static void ffs_dmabuf_release(struct kref *ref)
+{
+	struct ffs_dmabuf_priv *priv = container_of(ref, struct ffs_dmabuf_priv, ref);
+	struct dma_buf_attachment *attach = priv->attach;
+	struct dma_buf *dmabuf = attach->dmabuf;
+
+	pr_vdebug("FFS DMABUF release\n");
+	dma_resv_lock(dmabuf->resv, NULL);
+	dma_buf_unmap_attachment(attach, priv->sgt, priv->dir);
+	dma_resv_unlock(dmabuf->resv);
+
+	dma_buf_detach(attach->dmabuf, attach);
+	dma_buf_put(dmabuf);
+	kfree(priv);
+}
+
+static void ffs_dmabuf_get(struct dma_buf_attachment *attach)
+{
+	struct ffs_dmabuf_priv *priv = attach->importer_priv;
+
+	kref_get(&priv->ref);
+}
+
+static void ffs_dmabuf_put(struct dma_buf_attachment *attach)
+{
+	struct ffs_dmabuf_priv *priv = attach->importer_priv;
+
+	kref_put(&priv->ref, ffs_dmabuf_release);
+}
+
 static int
 ffs_epfile_release(struct inode *inode, struct file *file)
 {
 	struct ffs_epfile *epfile = inode->i_private;
+	struct ffs_dmabuf_priv *priv, *tmp;
+	struct ffs_data *ffs = epfile->ffs;
+
+	mutex_lock(&epfile->dmabufs_mutex);
+
+	/* Close all attached DMABUFs */
+	list_for_each_entry_safe(priv, tmp, &epfile->dmabufs, entry) {
+		/* Cancel any pending transfer */
+		spin_lock_irq(&ffs->eps_lock);
+		if (priv->ep && priv->req)
+			usb_ep_dequeue(priv->ep, priv->req);
+		spin_unlock_irq(&ffs->eps_lock);
+
+		list_del(&priv->entry);
+		ffs_dmabuf_put(priv->attach);
+	}
+
+	mutex_unlock(&epfile->dmabufs_mutex);
 
 	__ffs_epfile_read_buffer_free(epfile);
 	ffs_data_closed(epfile->ffs);
@@ -1282,6 +1359,356 @@ ffs_epfile_release(struct inode *inode, struct file *file)
 	return 0;
 }
 
+static void ffs_dmabuf_cleanup(struct work_struct *work)
+{
+	struct ffs_dma_fence *dma_fence =
+		container_of(work, struct ffs_dma_fence, work);
+	struct ffs_dmabuf_priv *priv = dma_fence->priv;
+	struct dma_buf_attachment *attach = priv->attach;
+	struct dma_fence *fence = &dma_fence->base;
+
+	ffs_dmabuf_put(attach);
+	dma_fence_put(fence);
+}
+
+static void ffs_dmabuf_signal_done(struct ffs_dma_fence *dma_fence, int ret)
+{
+	struct ffs_dmabuf_priv *priv = dma_fence->priv;
+	struct dma_fence *fence = &dma_fence->base;
+	bool cookie = dma_fence_begin_signalling();
+
+	dma_fence_get(fence);
+	fence->error = ret;
+	dma_fence_signal(fence);
+	dma_fence_end_signalling(cookie);
+
+	/*
+	 * The fence will be unref'd in ffs_dmabuf_cleanup.
+	 * It can't be done here, as the unref functions might try to lock
+	 * the resv object, which would deadlock.
+	 */
+	INIT_WORK(&dma_fence->work, ffs_dmabuf_cleanup);
+	queue_work(priv->ffs->io_completion_wq, &dma_fence->work);
+}
+
+static void ffs_epfile_dmabuf_io_complete(struct usb_ep *ep,
+					  struct usb_request *req)
+{
+	pr_vdebug("FFS: DMABUF transfer complete, status=%d\n", req->status);
+	ffs_dmabuf_signal_done(req->context, req->status);
+	usb_ep_free_request(ep, req);
+}
+
+static const char *ffs_dmabuf_get_driver_name(struct dma_fence *fence)
+{
+	return "functionfs";
+}
+
+static const char *ffs_dmabuf_get_timeline_name(struct dma_fence *fence)
+{
+	return "";
+}
+
+static void ffs_dmabuf_fence_release(struct dma_fence *fence)
+{
+	struct ffs_dma_fence *dma_fence =
+		container_of(fence, struct ffs_dma_fence, base);
+
+	kfree(dma_fence);
+}
+
+static const struct dma_fence_ops ffs_dmabuf_fence_ops = {
+	.get_driver_name	= ffs_dmabuf_get_driver_name,
+	.get_timeline_name	= ffs_dmabuf_get_timeline_name,
+	.release		= ffs_dmabuf_fence_release,
+};
+
+static int ffs_dma_resv_lock(struct dma_buf *dmabuf, bool nonblock)
+{
+	if (!nonblock)
+		return dma_resv_lock_interruptible(dmabuf->resv, NULL);
+
+	if (!dma_resv_trylock(dmabuf->resv))
+		return -EBUSY;
+
+	return 0;
+}
+
+static struct dma_buf_attachment *
+ffs_dmabuf_find_attachment(struct ffs_epfile *epfile, struct dma_buf *dmabuf)
+{
+	struct device *dev = epfile->ffs->gadget->dev.parent;
+	struct dma_buf_attachment *attach = NULL;
+	struct ffs_dmabuf_priv *priv;
+
+	mutex_lock(&epfile->dmabufs_mutex);
+
+	list_for_each_entry(priv, &epfile->dmabufs, entry) {
+		if (priv->attach->dev == dev
+		    && priv->attach->dmabuf == dmabuf) {
+			attach = priv->attach;
+			break;
+		}
+	}
+
+	if (attach)
+		ffs_dmabuf_get(attach);
+
+	mutex_unlock(&epfile->dmabufs_mutex);
+
+	return attach ?: ERR_PTR(-EPERM);
+}
+
+static int ffs_dmabuf_attach(struct file *file, int fd)
+{
+	bool nonblock = file->f_flags & O_NONBLOCK;
+	struct ffs_epfile *epfile = file->private_data;
+	struct usb_gadget *gadget = epfile->ffs->gadget;
+	struct dma_buf_attachment *attach;
+	struct ffs_dmabuf_priv *priv;
+	enum dma_data_direction dir;
+	struct sg_table *sg_table;
+	struct dma_buf *dmabuf;
+	int err;
+
+	if (!gadget || !gadget->sg_supported)
+		return -EPERM;
+
+	dmabuf = dma_buf_get(fd);
+	if (IS_ERR(dmabuf))
+		return PTR_ERR(dmabuf);
+
+	attach = dma_buf_attach(dmabuf, gadget->dev.parent);
+	if (IS_ERR(attach)) {
+		err = PTR_ERR(attach);
+		goto err_dmabuf_put;
+	}
+
+	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
+	if (!priv) {
+		err = -ENOMEM;
+		goto err_dmabuf_detach;
+	}
+
+	dir = epfile->in ? DMA_FROM_DEVICE : DMA_TO_DEVICE;
+
+	err = ffs_dma_resv_lock(dmabuf, nonblock);
+	if (err)
+		goto err_free_priv;
+
+	sg_table = dma_buf_map_attachment(attach, dir);
+	dma_resv_unlock(dmabuf->resv);
+
+	if (IS_ERR(sg_table)) {
+		err = PTR_ERR(sg_table);
+		goto err_free_priv;
+	}
+
+	attach->importer_priv = priv;
+
+	priv->sgt = sg_table;
+	priv->dir = dir;
+	priv->ffs = epfile->ffs;
+	priv->attach = attach;
+	spin_lock_init(&priv->lock);
+	kref_init(&priv->ref);
+	priv->context = dma_fence_context_alloc(1);
+
+	mutex_lock(&epfile->dmabufs_mutex);
+	list_add(&priv->entry, &epfile->dmabufs);
+	mutex_unlock(&epfile->dmabufs_mutex);
+
+	return 0;
+
+err_free_priv:
+	kfree(priv);
+err_dmabuf_detach:
+	dma_buf_detach(dmabuf, attach);
+err_dmabuf_put:
+	dma_buf_put(dmabuf);
+
+	return err;
+}
+
+static int ffs_dmabuf_detach(struct file *file, int fd)
+{
+	struct ffs_epfile *epfile = file->private_data;
+	struct ffs_data *ffs = epfile->ffs;
+	struct device *dev = ffs->gadget->dev.parent;
+	struct ffs_dmabuf_priv *priv, *tmp;
+	struct dma_buf *dmabuf;
+	int ret = -EPERM;
+
+	dmabuf = dma_buf_get(fd);
+	if (IS_ERR(dmabuf))
+		return PTR_ERR(dmabuf);
+
+	mutex_lock(&epfile->dmabufs_mutex);
+
+	list_for_each_entry_safe(priv, tmp, &epfile->dmabufs, entry) {
+		if (priv->attach->dev == dev
+		    && priv->attach->dmabuf == dmabuf) {
+			/* Cancel any pending transfer */
+			spin_lock_irq(&ffs->eps_lock);
+			if (priv->ep && priv->req)
+				usb_ep_dequeue(priv->ep, priv->req);
+			spin_unlock_irq(&ffs->eps_lock);
+
+			list_del(&priv->entry);
+
+			/* Unref the reference from ffs_dmabuf_attach() */
+			ffs_dmabuf_put(priv->attach);
+			ret = 0;
+			break;
+		}
+	}
+
+	mutex_unlock(&epfile->dmabufs_mutex);
+	dma_buf_put(dmabuf);
+
+	return ret;
+}
+
+static int ffs_dmabuf_transfer(struct file *file,
+			       const struct usb_ffs_dmabuf_transfer_req *req)
+{
+	bool nonblock = file->f_flags & O_NONBLOCK;
+	struct ffs_epfile *epfile = file->private_data;
+	struct dma_buf_attachment *attach;
+	struct ffs_dmabuf_priv *priv;
+	struct ffs_dma_fence *fence;
+	struct usb_request *usb_req;
+	struct dma_buf *dmabuf;
+	struct ffs_ep *ep;
+	bool cookie;
+	u32 seqno;
+	int ret;
+
+	if (req->flags & ~USB_FFS_DMABUF_TRANSFER_MASK)
+		return -EINVAL;
+
+	dmabuf = dma_buf_get(req->fd);
+	if (IS_ERR(dmabuf))
+		return PTR_ERR(dmabuf);
+
+	if (req->length > dmabuf->size || req->length == 0) {
+		ret = -EINVAL;
+		goto err_dmabuf_put;
+	}
+
+	attach = ffs_dmabuf_find_attachment(epfile, dmabuf);
+	if (IS_ERR(attach)) {
+		ret = PTR_ERR(attach);
+		goto err_dmabuf_put;
+	}
+
+	priv = attach->importer_priv;
+
+	ep = ffs_epfile_wait_ep(file);
+	if (IS_ERR(ep)) {
+		ret = PTR_ERR(ep);
+		goto err_attachment_put;
+	}
+
+	ret = ffs_dma_resv_lock(dmabuf, nonblock);
+	if (ret)
+		goto err_attachment_put;
+
+	/* Make sure we don't have writers */
+	if (!dma_resv_test_signaled(dmabuf->resv, DMA_RESV_USAGE_WRITE)) {
+		pr_vdebug("FFS WRITE fence is not signaled\n");
+		ret = -EBUSY;
+		goto err_resv_unlock;
+	}
+
+	/* If we're writing to the DMABUF, make sure we don't have readers */
+	if (epfile->in &&
+	    !dma_resv_test_signaled(dmabuf->resv, DMA_RESV_USAGE_READ)) {
+		pr_vdebug("FFS READ fence is not signaled\n");
+		ret = -EBUSY;
+		goto err_resv_unlock;
+	}
+
+	ret = dma_resv_reserve_fences(dmabuf->resv, 1);
+	if (ret)
+		goto err_resv_unlock;
+
+	fence = kmalloc(sizeof(*fence), GFP_KERNEL);
+	if (!fence) {
+		ret = -ENOMEM;
+		goto err_resv_unlock;
+	}
+
+	fence->priv = priv;
+
+	spin_lock_irq(&epfile->ffs->eps_lock);
+
+	/* In the meantime, endpoint got disabled or changed. */
+	if (epfile->ep != ep) {
+		ret = -ESHUTDOWN;
+		goto err_fence_put;
+	}
+
+	usb_req = usb_ep_alloc_request(ep->ep, GFP_ATOMIC);
+	if (!usb_req) {
+		ret = -ENOMEM;
+		goto err_fence_put;
+	}
+
+	/*
+	 * usb_ep_queue() guarantees that all transfers are processed in the
+	 * order they are enqueued, so we can use a simple incrementing
+	 * sequence number for the dma_fence.
+	 */
+	seqno = atomic_add_return(1, &epfile->seqno);
+
+	dma_fence_init(&fence->base, &ffs_dmabuf_fence_ops,
+		       &priv->lock, priv->context, seqno);
+
+	dma_resv_add_fence(dmabuf->resv, &fence->base,
+			   dma_resv_usage_rw(epfile->in));
+	dma_resv_unlock(dmabuf->resv);
+
+	/* Now that the dma_fence is in place, queue the transfer. */
+
+	usb_req->length = req->length;
+	usb_req->buf = NULL;
+	usb_req->sg = priv->sgt->sgl;
+	usb_req->num_sgs = sg_nents_for_len(priv->sgt->sgl, req->length);
+	usb_req->sg_was_mapped = true;
+	usb_req->context  = fence;
+	usb_req->complete = ffs_epfile_dmabuf_io_complete;
+
+	cookie = dma_fence_begin_signalling();
+	ret = usb_ep_queue(ep->ep, usb_req, GFP_ATOMIC);
+	dma_fence_end_signalling(cookie);
+	if (!ret) {
+		priv->req = usb_req;
+		priv->ep = ep->ep;
+	} else {
+		pr_warn("FFS: Failed to queue DMABUF: %d\n", ret);
+		ffs_dmabuf_signal_done(fence, ret);
+		usb_ep_free_request(ep->ep, usb_req);
+	}
+
+	spin_unlock_irq(&epfile->ffs->eps_lock);
+	dma_buf_put(dmabuf);
+
+	return ret;
+
+err_fence_put:
+	spin_unlock_irq(&epfile->ffs->eps_lock);
+	dma_fence_put(&fence->base);
+err_resv_unlock:
+	dma_resv_unlock(dmabuf->resv);
+err_attachment_put:
+	ffs_dmabuf_put(attach);
+err_dmabuf_put:
+	dma_buf_put(dmabuf);
+
+	return ret;
+}
+
 static long ffs_epfile_ioctl(struct file *file, unsigned code,
 			     unsigned long value)
 {
@@ -1292,6 +1719,44 @@ static long ffs_epfile_ioctl(struct file *file, unsigned code,
 	if (WARN_ON(epfile->ffs->state != FFS_ACTIVE))
 		return -ENODEV;
 
+	switch (code) {
+	case FUNCTIONFS_DMABUF_ATTACH:
+	{
+		int fd;
+
+		if (copy_from_user(&fd, (void __user *)value, sizeof(fd))) {
+			ret = -EFAULT;
+			break;
+		}
+
+		return ffs_dmabuf_attach(file, fd);
+	}
+	case FUNCTIONFS_DMABUF_DETACH:
+	{
+		int fd;
+
+		if (copy_from_user(&fd, (void __user *)value, sizeof(fd))) {
+			ret = -EFAULT;
+			break;
+		}
+
+		return ffs_dmabuf_detach(file, fd);
+	}
+	case FUNCTIONFS_DMABUF_TRANSFER:
+	{
+		struct usb_ffs_dmabuf_transfer_req req;
+
+		if (copy_from_user(&req, (void __user *)value, sizeof(req))) {
+			ret = -EFAULT;
+			break;
+		}
+
+		return ffs_dmabuf_transfer(file, &req);
+	}
+	default:
+		break;
+	}
+
 	/* Wait for endpoint to be enabled */
 	ep = ffs_epfile_wait_ep(file);
 	if (IS_ERR(ep))
@@ -1869,6 +2334,8 @@ static int ffs_epfiles_create(struct ffs_data *ffs)
 	for (i = 1; i <= count; ++i, ++epfile) {
 		epfile->ffs = ffs;
 		mutex_init(&epfile->mutex);
+		mutex_init(&epfile->dmabufs_mutex);
+		INIT_LIST_HEAD(&epfile->dmabufs);
 		if (ffs->user_flags & FUNCTIONFS_VIRTUAL_ADDR)
 			sprintf(epfile->name, "ep%02x", ffs->eps_addrmap[i]);
 		else
diff --git a/include/uapi/linux/usb/functionfs.h b/include/uapi/linux/usb/functionfs.h
index 078098e73fd3..9f88de9c3d66 100644
--- a/include/uapi/linux/usb/functionfs.h
+++ b/include/uapi/linux/usb/functionfs.h
@@ -86,6 +86,22 @@ struct usb_ext_prop_desc {
 	__le16	wPropertyNameLength;
 } __attribute__((packed));
 
+/* Flags for usb_ffs_dmabuf_transfer_req->flags (none for now) */
+#define USB_FFS_DMABUF_TRANSFER_MASK	0x0
+
+/**
+ * struct usb_ffs_dmabuf_transfer_req - Transfer request for a DMABUF object
+ * @fd:		file descriptor of the DMABUF object
+ * @flags:	one or more USB_FFS_DMABUF_TRANSFER_* flags
+ * @length:	number of bytes used in this DMABUF for the data transfer.
+ *		Should generally be set to the DMABUF's size.
+ */
+struct usb_ffs_dmabuf_transfer_req {
+	int fd;
+	__u32 flags;
+	__u64 length;
+} __attribute__((packed));
+
 #ifndef __KERNEL__
 
 /*
@@ -290,6 +306,31 @@ struct usb_functionfs_event {
 #define	FUNCTIONFS_ENDPOINT_DESC	_IOR('g', 130, \
 					     struct usb_endpoint_descriptor)
 
+/*
+ * Attach the DMABUF object, identified by its file descriptor, to the
+ * data endpoint. Returns zero on success, and a negative errno value
+ * on error.
+ */
+#define FUNCTIONFS_DMABUF_ATTACH	_IOW('g', 131, int)
+
 
+/*
+ * Detach the given DMABUF object, identified by its file descriptor,
+ * from the data endpoint. Returns zero on success, and a negative
+ * errno value on error. Note that closing the endpoint's file
+ * descriptor will automatically detach all attached DMABUFs.
+ */
+#define FUNCTIONFS_DMABUF_DETACH	_IOW('g', 132, int)
+
+/*
+ * Enqueue the previously attached DMABUF to the transfer queue.
+ * The argument is a structure that packs the DMABUF's file descriptor,
+ * the size in bytes to transfer (which should generally correspond to
+ * the size of the DMABUF), and a 'flags' field which is unused
+ * for now. Returns zero on success, and a negative errno value on
+ * error.
+ */
+#define FUNCTIONFS_DMABUF_TRANSFER	_IOW('g', 133, \
+					     struct usb_ffs_dmabuf_transfer_req)
 
 #endif /* _UAPI__LINUX_FUNCTIONFS_H__ */
-- 
2.43.0

[PATCH v6 4/4] Documentation: usb: Document FunctionFS DMABUF API

[Paul Cercueil]

Add documentation for the three ioctls used to attach or detach
externally-created DMABUFs, and to request transfers from/to previously
attached DMABUFs.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>

---
v3: New patch
---
 Documentation/usb/functionfs.rst | 36 ++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/Documentation/usb/functionfs.rst b/Documentation/usb/functionfs.rst
index a3054bea38f3..d05a775bc45b 100644
--- a/Documentation/usb/functionfs.rst
+++ b/Documentation/usb/functionfs.rst
@@ -2,6 +2,9 @@
 How FunctionFS works
 ====================
 
+Overview
+========
+
 From kernel point of view it is just a composite function with some
 unique behaviour.  It may be added to an USB configuration only after
 the user space driver has registered by writing descriptors and
@@ -66,3 +69,36 @@ have been written to their ep0's.
 
 Conversely, the gadget is unregistered after the first USB function
 closes its endpoints.
+
+DMABUF interface
+================
+
+FunctionFS additionally supports a DMABUF based interface, where the
+userspace can attach DMABUF objects (externally created) to an endpoint,
+and subsequently use them for data transfers.
+
+A userspace application can then use this interface to share DMABUF
+objects between several interfaces, allowing it to transfer data in a
+zero-copy fashion, for instance between IIO and the USB stack.
+
+As part of this interface, three new IOCTLs have been added. These three
+IOCTLs have to be performed on a data endpoint (ie. not ep0). They are:
+
+  ``FUNCTIONFS_DMABUF_ATTACH(int)``
+    Attach the DMABUF object, identified by its file descriptor, to the
+    data endpoint. Returns zero on success, and a negative errno value
+    on error.
+
+  ``FUNCTIONFS_DMABUF_DETACH(int)``
+    Detach the given DMABUF object, identified by its file descriptor,
+    from the data endpoint. Returns zero on success, and a negative
+    errno value on error. Note that closing the endpoint's file
+    descriptor will automatically detach all attached DMABUFs.
+
+  ``FUNCTIONFS_DMABUF_TRANSFER(struct usb_ffs_dmabuf_transfer_req *)``
+    Enqueue the previously attached DMABUF to the transfer queue.
+    The argument is a structure that packs the DMABUF's file descriptor,
+    the size in bytes to transfer (which should generally correspond to
+    the size of the DMABUF), and a 'flags' field which is unused
+    for now. Returns zero on success, and a negative errno value on
+    error.
-- 
2.43.0