[Linaro-mm-sig] Re: [PATCH v4 3/4] usb: gadget: functionfs: Add DMABUF import interface

Am 17.01.24 um 13:26 schrieb 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

I only looked at it from the DMA-buf maintainer point of view and especially the fence signaling (which people often get wrong) looks correct to me.

Can't judge if the USB side will work or not, so I can only give my Acked-by for this as well.

Regards, Christian.

---

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 dmabufs 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

---

drivers/usb/gadget/function/f_fs.c | 454 ++++++++++++++++++++++++++++ include/uapi/linux/usb/functionfs.h | 41 +++ 2 files changed, 495 insertions(+)

diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c index ed2a6d5fcef7..64dfd084c857 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 +129,23 @@ 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;
• spinlock_t lock;
• u64 context;

+};

+struct ffs_dma_fence {

• struct dma_fence base;
• struct ffs_dmabuf_priv *priv;
• struct sg_table *sgt;
• enum dma_data_direction dir;
• struct work_struct work;

+};

• struct ffs_epfile { /* Protects ep->ep and ep->req. */ struct mutex mutex;

@@ -197,6 +219,11 @@ 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 +1298,47 @@ 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_debug("FFS DMABUF release\n");
• 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;
• mutex_lock(&epfile->dmabufs_mutex);
• /* Close all attached DMABUFs */
• list_for_each_entry_safe(priv, tmp, &epfile->dmabufs, entry) {

• 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 +1346,356 @@ ffs_epfile_release(struct inode *inode, struct file *file) return 0; } +static void ffs_dmabuf_unmap_work(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;
• dma_resv_lock(attach->dmabuf->resv, NULL);
• dma_buf_unmap_attachment(attach, dma_fence->sgt, dma_fence->dir);
• dma_resv_unlock(attach->dmabuf->resv);
• 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();
• /*

• * The dma_buf_unmap_attachment() also perform cache-management.
  

• * In a perfect world this would be done before the DMA fence is
  

• * signaled; however this is not yet possible as
  

• * dma_buf_unmap_attachment() is not safe to use in the DMA fence's
  

• * critical section.
  

• */
  

• 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_unmap_work.
  

• * 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_unmap_work);
• 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_debug("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) +{

• struct ffs_epfile *epfile = file->private_data;
• struct usb_gadget *gadget = epfile->ffs->gadget;
• struct dma_buf_attachment *attach;
• struct ffs_dmabuf_priv *priv;
• 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;
  

• }
• attach->importer_priv = priv;
• 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_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 device *dev = epfile->ffs->gadget->dev.parent;
• struct ffs_dmabuf_priv *priv;
• 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(priv, &epfile->dmabufs, entry) {

• if (priv->attach->dev == dev
  

•     && priv->attach->dmabuf == dmabuf) {
  

• 	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 dma_to_ram, nonblock = file->f_flags & O_NONBLOCK;
• struct ffs_epfile *epfile = file->private_data;
• struct dma_buf_attachment *attach;
• struct ffs_dmabuf_priv *priv;
• enum dma_data_direction dir;
• struct ffs_dma_fence *fence;
• struct usb_request *usb_req;
• struct sg_table *sg_table;
• 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;
• if (epfile->in)

• dir = DMA_FROM_DEVICE;
  

• else

• dir = DMA_TO_DEVICE;
  

• 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_debug("FFS WRITE fence is not signaled\n");
  

• ret = -EBUSY;
  

• goto err_resv_unlock;
  

• }
• dma_to_ram = dir == DMA_FROM_DEVICE;
• /* If we're writing to the DMABUF, make sure we don't have readers */
• if (dma_to_ram &&

•    !dma_resv_test_signaled(dmabuf->resv, DMA_RESV_USAGE_READ)) {
  

• pr_debug("FFS READ fence is not signaled\n");
  

• ret = -EBUSY;
  

• goto err_resv_unlock;
  

• }
• sg_table = dma_buf_map_attachment(attach, dir);
• if (IS_ERR(sg_table)) {

• ret = PTR_ERR(sg_table);
  

• goto err_resv_unlock;
  

• }
• ret = dma_resv_reserve_fences(dmabuf->resv, 1);
• if (ret)

• goto err_unmap_attachment;
  

• fence = kmalloc(sizeof(*fence), GFP_KERNEL);
• if (!fence) {

• ret = -ENOMEM;
  

• goto err_resv_unlock;
  

• }
• fence->sgt = sg_table;
• fence->dir = dir;
• 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(dma_to_ram));
  

• 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 = sg_table->sgl;
• usb_req->num_sgs = sg_nents_for_len(sg_table->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) {

• 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_unmap_attachment:

• dma_buf_unmap_attachment(attach, sg_table, dir);

+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 +1706,44 @@ 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 +2321,8 @@ 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__ */