[PATCH v10 0/6] iio: new DMABUF based API v10

[PATCH v10 0/6] iio: new DMABUF based API v10

[Paul Cercueil]

Hi Jonathan,

Here is a revised (and hopefully final?) version of my DMABUF patchset.

This v10 removes the extra "flags" parameter of
dmaengine_prep_peripheral_dma_vec(), and adds kernel doc to the function
as Vinod requested.

As Nuno upstreamed support for output buffers, I (slightly) modified
patch 5/6 and now output buffers are supported with the DMABUF API.
All I did was remove a "fail if output" check really.

This was based on next-20240605.

Changelog:
- [1/6]:
  - Add kernel doc to dmaengine_prep_peripheral_dma_vec()
  - Remove extra flags parameter
- [2/6]:
  - Use the new function prototype (without the extra prep_flags).
- [5/6]:
  - Remove extra flags parameter to dmaengine_prep_peripheral_dma_vec()
  - Add support for TX transfers

Cheers,
-Paul

Paul Cercueil (6):
  dmaengine: Add API function dmaengine_prep_peripheral_dma_vec()
  dmaengine: dma-axi-dmac: Implement device_prep_peripheral_dma_vec
  iio: core: Add new DMABUF interface infrastructure
  iio: buffer-dma: Enable support for DMABUFs
  iio: buffer-dmaengine: Support new DMABUF based userspace API
  Documentation: iio: Document high-speed DMABUF based API

 Documentation/iio/iio_dmabuf_api.rst          |  54 ++
 Documentation/iio/index.rst                   |   1 +
 drivers/dma/dma-axi-dmac.c                    |  40 ++
 drivers/iio/Kconfig                           |   1 +
 drivers/iio/buffer/industrialio-buffer-dma.c  | 180 ++++++-
 .../buffer/industrialio-buffer-dmaengine.c    |  62 ++-
 drivers/iio/industrialio-buffer.c             | 462 ++++++++++++++++++
 include/linux/dmaengine.h                     |  33 ++
 include/linux/iio/buffer-dma.h                |  31 ++
 include/linux/iio/buffer_impl.h               |  30 ++
 include/uapi/linux/iio/buffer.h               |  22 +
 11 files changed, 896 insertions(+), 20 deletions(-)
 create mode 100644 Documentation/iio/iio_dmabuf_api.rst

-- 
2.43.0

[PATCH v10 1/6] dmaengine: Add API function dmaengine_prep_peripheral_dma_vec()

[Paul Cercueil]

This function can be used to initiate a scatter-gather DMA transfer,
where the address and size of each segment is located in one entry of
the dma_vec array.

The major difference with dmaengine_prep_slave_sg() is that it supports
specifying the lengths of each DMA transfer; as trying to override the
length of the transfer with dmaengine_prep_slave_sg() is a very tedious
process. The introduction of a new API function is also justified by the
fact that scatterlists are on their way out.

Note that dmaengine_prep_interleaved_dma() is not helpful either in that
case, as it assumes that the address of each segment will be higher than
the one of the previous segment, which we just cannot guarantee in case
of a scatter-gather transfer.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Nuno Sa <nuno.sa@analog.com>

---
v3: New patch

v5: Replace with function dmaengine_prep_slave_dma_vec(), and struct
    'dma_vec'.
    Note that at some point we will need to support cyclic transfers
    using dmaengine_prep_slave_dma_vec(). Maybe with a new "flags"
    parameter to the function?

v7:
  - Renamed *device_prep_slave_dma_vec() -> device_prep_peripheral_dma_vec();
  - Added a new flag parameter to the function as agreed between Paul
    and Vinod. I renamed the first parameter to prep_flags as it's supposed to
    be used (I think) with enum dma_ctrl_flags. I'm not really sure how that API
    can grow but I was thinking in just having a bool cyclic parameter (as the
    first intention of the flags is to support cyclic transfers) but ended up
    "respecting" the previously agreed approach.

v10:
  - Add kernel doc to dmaengine_prep_peripheral_dma_vec()
  - Remove extra flags parameter
---
 include/linux/dmaengine.h | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
index 752dbde4cec1..9fc03068cabc 100644
--- a/include/linux/dmaengine.h
+++ b/include/linux/dmaengine.h
@@ -160,6 +160,16 @@ struct dma_interleaved_template {
 	struct data_chunk sgl[];
 };
 
+/**
+ * struct dma_vec - DMA vector
+ * @addr: Bus address of the start of the vector
+ * @len: Length in bytes of the DMA vector
+ */
+struct dma_vec {
+	dma_addr_t addr;
+	size_t len;
+};
+
 /**
  * enum dma_ctrl_flags - DMA flags to augment operation preparation,
  *  control completion, and communicate status.
@@ -910,6 +920,10 @@ struct dma_device {
 	struct dma_async_tx_descriptor *(*device_prep_dma_interrupt)(
 		struct dma_chan *chan, unsigned long flags);
 
+	struct dma_async_tx_descriptor *(*device_prep_peripheral_dma_vec)(
+		struct dma_chan *chan, const struct dma_vec *vecs,
+		size_t nents, enum dma_transfer_direction direction,
+		unsigned long flags);
 	struct dma_async_tx_descriptor *(*device_prep_slave_sg)(
 		struct dma_chan *chan, struct scatterlist *sgl,
 		unsigned int sg_len, enum dma_transfer_direction direction,
@@ -973,6 +987,25 @@ static inline struct dma_async_tx_descriptor *dmaengine_prep_slave_single(
 						  dir, flags, NULL);
 }
 
+/**
+ * dmaengine_prep_peripheral_dma_vec() - Prepare a DMA scatter-gather descriptor
+ * @chan: The channel to be used for this descriptor
+ * @vecs: The array of DMA vectors that should be transferred
+ * @nents: The number of DMA vectors in the array
+ * @dir: Specifies the direction of the data transfer
+ * @flags: DMA engine flags
+ */
+static inline struct dma_async_tx_descriptor *dmaengine_prep_peripheral_dma_vec(
+	struct dma_chan *chan, const struct dma_vec *vecs, size_t nents,
+	enum dma_transfer_direction dir, unsigned long flags)
+{
+	if (!chan || !chan->device || !chan->device->device_prep_peripheral_dma_vec)
+		return NULL;
+
+	return chan->device->device_prep_peripheral_dma_vec(chan, vecs, nents,
+							    dir, flags);
+}
+
 static inline struct dma_async_tx_descriptor *dmaengine_prep_slave_sg(
 	struct dma_chan *chan, struct scatterlist *sgl,	unsigned int sg_len,
 	enum dma_transfer_direction dir, unsigned long flags)
-- 
2.43.0

Re: [PATCH v10 1/6] dmaengine: Add API function dmaengine_prep_peripheral_dma_vec()

[Vinod Koul]

On 05-06-24, 13:08, Paul Cercueil wrote:
> This function can be used to initiate a scatter-gather DMA transfer,
> where the address and size of each segment is located in one entry of
> the dma_vec array.
> 
> The major difference with dmaengine_prep_slave_sg() is that it supports
> specifying the lengths of each DMA transfer; as trying to override the
> length of the transfer with dmaengine_prep_slave_sg() is a very tedious
> process. The introduction of a new API function is also justified by the
> fact that scatterlists are on their way out.
> 
> Note that dmaengine_prep_interleaved_dma() is not helpful either in that
> case, as it assumes that the address of each segment will be higher than
> the one of the previous segment, which we just cannot guarantee in case
> of a scatter-gather transfer.

This looks good to me, but is missing Documentation changes for this
API, pls add that

> 
> Signed-off-by: Paul Cercueil <paul@crapouillou.net>
> Signed-off-by: Nuno Sa <nuno.sa@analog.com>
> 
> ---
> v3: New patch
> 
> v5: Replace with function dmaengine_prep_slave_dma_vec(), and struct
>     'dma_vec'.
>     Note that at some point we will need to support cyclic transfers
>     using dmaengine_prep_slave_dma_vec(). Maybe with a new "flags"
>     parameter to the function?
> 
> v7:
>   - Renamed *device_prep_slave_dma_vec() -> device_prep_peripheral_dma_vec();
>   - Added a new flag parameter to the function as agreed between Paul
>     and Vinod. I renamed the first parameter to prep_flags as it's supposed to
>     be used (I think) with enum dma_ctrl_flags. I'm not really sure how that API
>     can grow but I was thinking in just having a bool cyclic parameter (as the
>     first intention of the flags is to support cyclic transfers) but ended up
>     "respecting" the previously agreed approach.
> 
> v10:
>   - Add kernel doc to dmaengine_prep_peripheral_dma_vec()
>   - Remove extra flags parameter
> ---
>  include/linux/dmaengine.h | 33 +++++++++++++++++++++++++++++++++
>  1 file changed, 33 insertions(+)
> 
> diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> index 752dbde4cec1..9fc03068cabc 100644
> --- a/include/linux/dmaengine.h
> +++ b/include/linux/dmaengine.h
> @@ -160,6 +160,16 @@ struct dma_interleaved_template {
>  	struct data_chunk sgl[];
>  };
>  
> +/**
> + * struct dma_vec - DMA vector
> + * @addr: Bus address of the start of the vector
> + * @len: Length in bytes of the DMA vector
> + */
> +struct dma_vec {
> +	dma_addr_t addr;
> +	size_t len;
> +};
> +
>  /**
>   * enum dma_ctrl_flags - DMA flags to augment operation preparation,
>   *  control completion, and communicate status.
> @@ -910,6 +920,10 @@ struct dma_device {
>  	struct dma_async_tx_descriptor *(*device_prep_dma_interrupt)(
>  		struct dma_chan *chan, unsigned long flags);
>  
> +	struct dma_async_tx_descriptor *(*device_prep_peripheral_dma_vec)(
> +		struct dma_chan *chan, const struct dma_vec *vecs,
> +		size_t nents, enum dma_transfer_direction direction,
> +		unsigned long flags);
>  	struct dma_async_tx_descriptor *(*device_prep_slave_sg)(
>  		struct dma_chan *chan, struct scatterlist *sgl,
>  		unsigned int sg_len, enum dma_transfer_direction direction,
> @@ -973,6 +987,25 @@ static inline struct dma_async_tx_descriptor *dmaengine_prep_slave_single(
>  						  dir, flags, NULL);
>  }
>  
> +/**
> + * dmaengine_prep_peripheral_dma_vec() - Prepare a DMA scatter-gather descriptor
> + * @chan: The channel to be used for this descriptor
> + * @vecs: The array of DMA vectors that should be transferred
> + * @nents: The number of DMA vectors in the array
> + * @dir: Specifies the direction of the data transfer
> + * @flags: DMA engine flags
> + */
> +static inline struct dma_async_tx_descriptor *dmaengine_prep_peripheral_dma_vec(
> +	struct dma_chan *chan, const struct dma_vec *vecs, size_t nents,
> +	enum dma_transfer_direction dir, unsigned long flags)
> +{
> +	if (!chan || !chan->device || !chan->device->device_prep_peripheral_dma_vec)
> +		return NULL;
> +
> +	return chan->device->device_prep_peripheral_dma_vec(chan, vecs, nents,
> +							    dir, flags);
> +}
> +
>  static inline struct dma_async_tx_descriptor *dmaengine_prep_slave_sg(
>  	struct dma_chan *chan, struct scatterlist *sgl,	unsigned int sg_len,
>  	enum dma_transfer_direction dir, unsigned long flags)
> -- 
> 2.43.0

-- 
~Vinod

[PATCH v10 2/6] dmaengine: dma-axi-dmac: Implement device_prep_peripheral_dma_vec

[Paul Cercueil]

Add implementation of the .device_prep_peripheral_dma_vec() callback.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Nuno Sa <nuno.sa@analog.com>

---
v3: New patch

v5: Implement .device_prep_slave_dma_vec() instead of v3's
    .device_prep_slave_dma_array().

v6: Use new prototype for axi_dmac_alloc_desc() as it changed upstream.

v7: Adapted patch for the changes made in patch 1.

v10: Use the new function prototype (without the extra prep_flags).
---
 drivers/dma/dma-axi-dmac.c | 40 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/drivers/dma/dma-axi-dmac.c b/drivers/dma/dma-axi-dmac.c
index bdb752f11869..36943b0c6d60 100644
--- a/drivers/dma/dma-axi-dmac.c
+++ b/drivers/dma/dma-axi-dmac.c
@@ -620,6 +620,45 @@ static struct axi_dmac_sg *axi_dmac_fill_linear_sg(struct axi_dmac_chan *chan,
 	return sg;
 }
 
+static struct dma_async_tx_descriptor *
+axi_dmac_prep_peripheral_dma_vec(struct dma_chan *c, const struct dma_vec *vecs,
+				 size_t nb, enum dma_transfer_direction direction,
+				 unsigned long flags)
+{
+	struct axi_dmac_chan *chan = to_axi_dmac_chan(c);
+	struct axi_dmac_desc *desc;
+	unsigned int num_sgs = 0;
+	struct axi_dmac_sg *dsg;
+	size_t i;
+
+	if (direction != chan->direction)
+		return NULL;
+
+	for (i = 0; i < nb; i++)
+		num_sgs += DIV_ROUND_UP(vecs[i].len, chan->max_length);
+
+	desc = axi_dmac_alloc_desc(chan, num_sgs);
+	if (!desc)
+		return NULL;
+
+	dsg = desc->sg;
+
+	for (i = 0; i < nb; i++) {
+		if (!axi_dmac_check_addr(chan, vecs[i].addr) ||
+		    !axi_dmac_check_len(chan, vecs[i].len)) {
+			kfree(desc);
+			return NULL;
+		}
+
+		dsg = axi_dmac_fill_linear_sg(chan, direction, vecs[i].addr, 1,
+					      vecs[i].len, dsg);
+	}
+
+	desc->cyclic = false;
+
+	return vchan_tx_prep(&chan->vchan, &desc->vdesc, flags);
+}
+
 static struct dma_async_tx_descriptor *axi_dmac_prep_slave_sg(
 	struct dma_chan *c, struct scatterlist *sgl,
 	unsigned int sg_len, enum dma_transfer_direction direction,
@@ -1061,6 +1100,7 @@ static int axi_dmac_probe(struct platform_device *pdev)
 	dma_dev->device_tx_status = dma_cookie_status;
 	dma_dev->device_issue_pending = axi_dmac_issue_pending;
 	dma_dev->device_prep_slave_sg = axi_dmac_prep_slave_sg;
+	dma_dev->device_prep_peripheral_dma_vec = axi_dmac_prep_peripheral_dma_vec;
 	dma_dev->device_prep_dma_cyclic = axi_dmac_prep_dma_cyclic;
 	dma_dev->device_prep_interleaved_dma = axi_dmac_prep_interleaved;
 	dma_dev->device_terminate_all = axi_dmac_terminate_all;
-- 
2.43.0

[PATCH v10 3/6] iio: core: Add new DMABUF interface infrastructure

[Paul Cercueil]

Add the necessary infrastructure to the IIO core to support a new
optional DMABUF based interface.

With this new interface, DMABUF objects (externally created) can be
attached to a IIO buffer, and subsequently used for data transfer.

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.

The userspace application can also memory-map the DMABUF objects, and
access the sample data directly. The advantage of doing this vs. the
read() interface is that it avoids an extra copy of the data between the
kernel and userspace. This is particularly userful for high-speed
devices which produce several megabytes or even gigabytes of data per
second.

As part of the interface, 3 new IOCTLs have been added:

IIO_BUFFER_DMABUF_ATTACH_IOCTL(int fd):
 Attach the DMABUF object identified by the given file descriptor to the
 buffer.

IIO_BUFFER_DMABUF_DETACH_IOCTL(int fd):
 Detach the DMABUF object identified by the given file descriptor from
 the buffer. Note that closing the IIO buffer's file descriptor will
 automatically detach all previously attached DMABUF objects.

IIO_BUFFER_DMABUF_ENQUEUE_IOCTL(struct iio_dmabuf *):
 Request a data transfer to/from the given DMABUF object. Its file
 descriptor, as well as the transfer size and flags are provided in the
 "iio_dmabuf" structure.

These three IOCTLs have to be performed on the IIO buffer's file
descriptor, obtained using the IIO_BUFFER_GET_FD_IOCTL() ioctl.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Nuno Sa <nuno.sa@analog.com>

---
v2: Only allow the new IOCTLs on the buffer FD created with
    IIO_BUFFER_GET_FD_IOCTL().

v3: - Get rid of the old IOCTLs. The IIO subsystem does not create or
    manage DMABUFs anymore, and only attaches/detaches externally
    created DMABUFs.
    - Add IIO_BUFFER_DMABUF_CYCLIC to the supported flags.

v5: - Use dev_err() instead of pr_err()
    - Inline to_iio_dma_fence()
    - Add comment to explain why we unref twice when detaching dmabuf
    - Remove TODO comment. It is actually safe to free the file's
      private data even when transfers are still pending because it
      won't be accessed.
    - Fix documentation of new fields in struct iio_buffer_access_funcs
    - iio_dma_resv_lock() does not need to be exported, make it static

v6: - Remove dead code in iio_dma_resv_lock()
    - Fix non-block actually blocking
    - Cache dma_buf_attachment instead of mapping/unmapping it for every
      transfer
    - Return -EINVAL instead of IIO_IOCTL_UNHANDLED for unknown ioctl
    - Make .block_enqueue() callback take a dma_fence pointer, which
      will be passed to iio_buffer_signal_dmabuf_done() instead of the
      dma_buf_attachment; and remove the backpointer from the priv
      structure to the dma_fence.
    - Use dma_fence_begin/end_signalling in the dma_fence critical
      sections
    - Unref dma_fence and dma_buf_attachment in worker, because they
      might try to lock the dma_resv, which would deadlock.
    - Add buffer ops to lock/unlock the queue. This is motivated by the
      fact that once the dma_fence has been installed, we cannot lock
      anything anymore - so the queue must be locked before the
      dma_fence is installed.
    - Use 'long retl' variable to handle the return value of
      dma_resv_wait_timeout()
    - Protect dmabufs list access with a mutex
    - Rework iio_buffer_find_attachment() to use the internal dmabufs
      list, instead of messing with dmabufs private data.
    - Add an atomically-increasing sequence number for fences

v8  - Fix swapped fence direction
    - Simplify fence wait mechanism
    - Remove "Buffer closed with active transfers" print, as it was dead
      code
    - Un-export iio_buffer_dmabuf_{get,put}. They are not used anywhere
      else so they can even be static.
    - Prevent attaching already-attached DMABUFs

v9: - Select DMA_SHARED_BUFFER in Kconfig
    - Remove useless forward declaration of 'iio_dma_fence'
    - Import DMA-BUF namespace
    - Add missing __user tag to iio_buffer_detach_dmabuf() argument
---
 drivers/iio/Kconfig               |   1 +
 drivers/iio/industrialio-buffer.c | 462 ++++++++++++++++++++++++++++++
 include/linux/iio/buffer_impl.h   |  30 ++
 include/uapi/linux/iio/buffer.h   |  22 ++
 4 files changed, 515 insertions(+)

diff --git a/drivers/iio/Kconfig b/drivers/iio/Kconfig
index 9c351ffc7bed..661127aed2f9 100644
--- a/drivers/iio/Kconfig
+++ b/drivers/iio/Kconfig
@@ -14,6 +14,7 @@ if IIO
 
 config IIO_BUFFER
 	bool "Enable buffer support within IIO"
+	select DMA_SHARED_BUFFER
 	help
 	  Provide core support for various buffer based data
 	  acquisition methods.
diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
index 0138b21b244f..c98c8ac83785 100644
--- a/drivers/iio/industrialio-buffer.c
+++ b/drivers/iio/industrialio-buffer.c
@@ -9,15 +9,20 @@
  * - Better memory allocation techniques?
  * - Alternative access techniques?
  */
+#include <linux/atomic.h>
 #include <linux/anon_inodes.h>
 #include <linux/cleanup.h>
 #include <linux/kernel.h>
 #include <linux/export.h>
 #include <linux/device.h>
+#include <linux/dma-buf.h>
+#include <linux/dma-fence.h>
+#include <linux/dma-resv.h>
 #include <linux/file.h>
 #include <linux/fs.h>
 #include <linux/cdev.h>
 #include <linux/slab.h>
+#include <linux/mm.h>
 #include <linux/poll.h>
 #include <linux/sched/signal.h>
 
@@ -29,6 +34,32 @@
 #include <linux/iio/buffer.h>
 #include <linux/iio/buffer_impl.h>
 
+#define DMABUF_ENQUEUE_TIMEOUT_MS 5000
+
+MODULE_IMPORT_NS(DMA_BUF);
+
+struct iio_dmabuf_priv {
+	struct list_head entry;
+	struct kref ref;
+
+	struct iio_buffer *buffer;
+	struct iio_dma_buffer_block *block;
+
+	u64 context;
+	spinlock_t lock;
+
+	struct dma_buf_attachment *attach;
+	struct sg_table *sgt;
+	enum dma_data_direction dir;
+	atomic_t seqno;
+};
+
+struct iio_dma_fence {
+	struct dma_fence base;
+	struct iio_dmabuf_priv *priv;
+	struct work_struct work;
+};
+
 static const char * const iio_endian_prefix[] = {
 	[IIO_BE] = "be",
 	[IIO_LE] = "le",
@@ -333,6 +364,8 @@ void iio_buffer_init(struct iio_buffer *buffer)
 {
 	INIT_LIST_HEAD(&buffer->demux_list);
 	INIT_LIST_HEAD(&buffer->buffer_list);
+	INIT_LIST_HEAD(&buffer->dmabufs);
+	mutex_init(&buffer->dmabufs_mutex);
 	init_waitqueue_head(&buffer->pollq);
 	kref_init(&buffer->ref);
 	if (!buffer->watermark)
@@ -1526,14 +1559,57 @@ static void iio_buffer_unregister_legacy_sysfs_groups(struct iio_dev *indio_dev)
 	kfree(iio_dev_opaque->legacy_scan_el_group.attrs);
 }
 
+static void iio_buffer_dmabuf_release(struct kref *ref)
+{
+	struct iio_dmabuf_priv *priv = container_of(ref, struct iio_dmabuf_priv, ref);
+	struct dma_buf_attachment *attach = priv->attach;
+	struct iio_buffer *buffer = priv->buffer;
+	struct dma_buf *dmabuf = attach->dmabuf;
+
+	dma_resv_lock(dmabuf->resv, NULL);
+	dma_buf_unmap_attachment(attach, priv->sgt, priv->dir);
+	dma_resv_unlock(dmabuf->resv);
+
+	buffer->access->detach_dmabuf(buffer, priv->block);
+
+	dma_buf_detach(attach->dmabuf, attach);
+	dma_buf_put(dmabuf);
+	kfree(priv);
+}
+
+static void iio_buffer_dmabuf_get(struct dma_buf_attachment *attach)
+{
+	struct iio_dmabuf_priv *priv = attach->importer_priv;
+
+	kref_get(&priv->ref);
+}
+
+static void iio_buffer_dmabuf_put(struct dma_buf_attachment *attach)
+{
+	struct iio_dmabuf_priv *priv = attach->importer_priv;
+
+	kref_put(&priv->ref, iio_buffer_dmabuf_release);
+}
+
 static int iio_buffer_chrdev_release(struct inode *inode, struct file *filep)
 {
 	struct iio_dev_buffer_pair *ib = filep->private_data;
 	struct iio_dev *indio_dev = ib->indio_dev;
 	struct iio_buffer *buffer = ib->buffer;
+	struct iio_dmabuf_priv *priv, *tmp;
 
 	wake_up(&buffer->pollq);
 
+	mutex_lock(&buffer->dmabufs_mutex);
+
+	/* Close all attached DMABUFs */
+	list_for_each_entry_safe(priv, tmp, &buffer->dmabufs, entry) {
+		list_del_init(&priv->entry);
+		iio_buffer_dmabuf_put(priv->attach);
+	}
+
+	mutex_unlock(&buffer->dmabufs_mutex);
+
 	kfree(ib);
 	clear_bit(IIO_BUSY_BIT_POS, &buffer->flags);
 	iio_device_put(indio_dev);
@@ -1541,11 +1617,396 @@ static int iio_buffer_chrdev_release(struct inode *inode, struct file *filep)
 	return 0;
 }
 
+static int iio_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 *
+iio_buffer_find_attachment(struct iio_dev_buffer_pair *ib,
+			   struct dma_buf *dmabuf, bool nonblock)
+{
+	struct device *dev = ib->indio_dev->dev.parent;
+	struct iio_buffer *buffer = ib->buffer;
+	struct dma_buf_attachment *attach = NULL;
+	struct iio_dmabuf_priv *priv;
+
+	mutex_lock(&buffer->dmabufs_mutex);
+
+	list_for_each_entry(priv, &buffer->dmabufs, entry) {
+		if (priv->attach->dev == dev
+		    && priv->attach->dmabuf == dmabuf) {
+			attach = priv->attach;
+			break;
+		}
+	}
+
+	if (attach)
+		iio_buffer_dmabuf_get(attach);
+
+	mutex_unlock(&buffer->dmabufs_mutex);
+
+	return attach ?: ERR_PTR(-EPERM);
+}
+
+static int iio_buffer_attach_dmabuf(struct iio_dev_buffer_pair *ib,
+				    int __user *user_fd, bool nonblock)
+{
+	struct iio_dev *indio_dev = ib->indio_dev;
+	struct iio_buffer *buffer = ib->buffer;
+	struct dma_buf_attachment *attach;
+	struct iio_dmabuf_priv *priv, *each;
+	struct dma_buf *dmabuf;
+	int err, fd;
+
+	if (!buffer->access->attach_dmabuf
+	    || !buffer->access->detach_dmabuf
+	    || !buffer->access->enqueue_dmabuf)
+		return -EPERM;
+
+	if (copy_from_user(&fd, user_fd, sizeof(fd)))
+		return -EFAULT;
+
+	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	spin_lock_init(&priv->lock);
+	priv->context = dma_fence_context_alloc(1);
+
+	dmabuf = dma_buf_get(fd);
+	if (IS_ERR(dmabuf)) {
+		err = PTR_ERR(dmabuf);
+		goto err_free_priv;
+	}
+
+	attach = dma_buf_attach(dmabuf, indio_dev->dev.parent);
+	if (IS_ERR(attach)) {
+		err = PTR_ERR(attach);
+		goto err_dmabuf_put;
+	}
+
+	err = iio_dma_resv_lock(dmabuf, nonblock);
+	if (err)
+		goto err_dmabuf_detach;
+
+	priv->dir = buffer->direction == IIO_BUFFER_DIRECTION_IN
+		? DMA_FROM_DEVICE : DMA_TO_DEVICE;
+
+	priv->sgt = dma_buf_map_attachment(attach, priv->dir);
+	if (IS_ERR(priv->sgt)) {
+		err = PTR_ERR(priv->sgt);
+		dev_err(&indio_dev->dev, "Unable to map attachment: %d\n", err);
+		goto err_resv_unlock;
+	}
+
+	kref_init(&priv->ref);
+	priv->buffer = buffer;
+	priv->attach = attach;
+	attach->importer_priv = priv;
+
+	priv->block = buffer->access->attach_dmabuf(buffer, attach);
+	if (IS_ERR(priv->block)) {
+		err = PTR_ERR(priv->block);
+		goto err_dmabuf_unmap_attachment;
+	}
+
+	dma_resv_unlock(dmabuf->resv);
+
+	mutex_lock(&buffer->dmabufs_mutex);
+
+	/*
+	 * Check whether we already have an attachment for this driver/DMABUF
+	 * combo. If we do, refuse to attach.
+	 */
+	list_for_each_entry(each, &buffer->dmabufs, entry) {
+		if (each->attach->dev == indio_dev->dev.parent
+		    && each->attach->dmabuf == dmabuf) {
+			/*
+			 * We unlocked the reservation object, so going through
+			 * the cleanup code would mean re-locking it first.
+			 * At this stage it is simpler to free the attachment
+			 * using iio_buffer_dma_put().
+			 */
+			mutex_unlock(&buffer->dmabufs_mutex);
+			iio_buffer_dmabuf_put(attach);
+			return -EBUSY;
+		}
+	}
+
+	/* Otherwise, add the new attachment to our dmabufs list. */
+	list_add(&priv->entry, &buffer->dmabufs);
+	mutex_unlock(&buffer->dmabufs_mutex);
+
+	return 0;
+
+err_dmabuf_unmap_attachment:
+	dma_buf_unmap_attachment(attach, priv->sgt, priv->dir);
+err_resv_unlock:
+	dma_resv_unlock(dmabuf->resv);
+err_dmabuf_detach:
+	dma_buf_detach(dmabuf, attach);
+err_dmabuf_put:
+	dma_buf_put(dmabuf);
+err_free_priv:
+	kfree(priv);
+
+	return err;
+}
+
+static int iio_buffer_detach_dmabuf(struct iio_dev_buffer_pair *ib,
+				    int __user *user_req, bool nonblock)
+{
+	struct iio_buffer *buffer = ib->buffer;
+	struct iio_dev *indio_dev = ib->indio_dev;
+	struct iio_dmabuf_priv *priv;
+	struct dma_buf *dmabuf;
+	int dmabuf_fd, ret = -EPERM;
+
+	if (copy_from_user(&dmabuf_fd, user_req, sizeof(dmabuf_fd)))
+		return -EFAULT;
+
+	dmabuf = dma_buf_get(dmabuf_fd);
+	if (IS_ERR(dmabuf))
+		return PTR_ERR(dmabuf);
+
+	mutex_lock(&buffer->dmabufs_mutex);
+
+	list_for_each_entry(priv, &buffer->dmabufs, entry) {
+		if (priv->attach->dev == indio_dev->dev.parent
+		    && priv->attach->dmabuf == dmabuf) {
+			list_del(&priv->entry);
+
+			/* Unref the reference from iio_buffer_attach_dmabuf() */
+			iio_buffer_dmabuf_put(priv->attach);
+			ret = 0;
+			break;
+		}
+	}
+
+	mutex_unlock(&buffer->dmabufs_mutex);
+	dma_buf_put(dmabuf);
+
+	return ret;
+}
+
+static const char *
+iio_buffer_dma_fence_get_driver_name(struct dma_fence *fence)
+{
+	return "iio";
+}
+
+static void iio_buffer_dma_fence_release(struct dma_fence *fence)
+{
+	struct iio_dma_fence *iio_fence =
+		container_of(fence, struct iio_dma_fence, base);
+
+	kfree(iio_fence);
+}
+
+static const struct dma_fence_ops iio_buffer_dma_fence_ops = {
+	.get_driver_name	= iio_buffer_dma_fence_get_driver_name,
+	.get_timeline_name	= iio_buffer_dma_fence_get_driver_name,
+	.release		= iio_buffer_dma_fence_release,
+};
+
+static int iio_buffer_enqueue_dmabuf(struct iio_dev_buffer_pair *ib,
+				     struct iio_dmabuf __user *iio_dmabuf_req,
+				     bool nonblock)
+{
+	struct iio_buffer *buffer = ib->buffer;
+	struct iio_dmabuf iio_dmabuf;
+	struct dma_buf_attachment *attach;
+	struct iio_dmabuf_priv *priv;
+	struct iio_dma_fence *fence;
+	struct dma_buf *dmabuf;
+	unsigned long timeout;
+	bool cookie, cyclic, dma_to_ram;
+	long retl;
+	u32 seqno;
+	int ret;
+
+	if (copy_from_user(&iio_dmabuf, iio_dmabuf_req, sizeof(iio_dmabuf)))
+		return -EFAULT;
+
+	if (iio_dmabuf.flags & ~IIO_BUFFER_DMABUF_SUPPORTED_FLAGS)
+		return -EINVAL;
+
+	cyclic = iio_dmabuf.flags & IIO_BUFFER_DMABUF_CYCLIC;
+
+	/* Cyclic flag is only supported on output buffers */
+	if (cyclic && buffer->direction != IIO_BUFFER_DIRECTION_OUT)
+		return -EINVAL;
+
+	dmabuf = dma_buf_get(iio_dmabuf.fd);
+	if (IS_ERR(dmabuf))
+		return PTR_ERR(dmabuf);
+
+	if (!iio_dmabuf.bytes_used || iio_dmabuf.bytes_used > dmabuf->size) {
+		ret = -EINVAL;
+		goto err_dmabuf_put;
+	}
+
+	attach = iio_buffer_find_attachment(ib, dmabuf, nonblock);
+	if (IS_ERR(attach)) {
+		ret = PTR_ERR(attach);
+		goto err_dmabuf_put;
+	}
+
+	priv = attach->importer_priv;
+
+	fence = kmalloc(sizeof(*fence), GFP_KERNEL);
+	if (!fence) {
+		ret = -ENOMEM;
+		goto err_attachment_put;
+	}
+
+	fence->priv = priv;
+
+	seqno = atomic_add_return(1, &priv->seqno);
+
+	/*
+	 * The transfers are guaranteed to be processed in the order they are
+	 * enqueued, so we can use a simple incrementing sequence number for
+	 * the dma_fence.
+	 */
+	dma_fence_init(&fence->base, &iio_buffer_dma_fence_ops,
+		       &priv->lock, priv->context, seqno);
+
+	ret = iio_dma_resv_lock(dmabuf, nonblock);
+	if (ret)
+		goto err_fence_put;
+
+	timeout = nonblock ? 0 : msecs_to_jiffies(DMABUF_ENQUEUE_TIMEOUT_MS);
+	dma_to_ram = buffer->direction == IIO_BUFFER_DIRECTION_IN;
+
+	/* Make sure we don't have writers */
+	retl = dma_resv_wait_timeout(dmabuf->resv,
+				     dma_resv_usage_rw(dma_to_ram),
+				     true, timeout);
+	if (retl == 0)
+		retl = -EBUSY;
+	if (retl < 0) {
+		ret = (int)retl;
+		goto err_resv_unlock;
+	}
+
+	if (buffer->access->lock_queue)
+		buffer->access->lock_queue(buffer);
+
+	ret = dma_resv_reserve_fences(dmabuf->resv, 1);
+	if (ret)
+		goto err_queue_unlock;
+
+	dma_resv_add_fence(dmabuf->resv, &fence->base,
+			   dma_to_ram ? DMA_RESV_USAGE_WRITE : DMA_RESV_USAGE_READ);
+	dma_resv_unlock(dmabuf->resv);
+
+	cookie = dma_fence_begin_signalling();
+
+	ret = buffer->access->enqueue_dmabuf(buffer, priv->block, &fence->base,
+					     priv->sgt, iio_dmabuf.bytes_used,
+					     cyclic);
+	if (ret) {
+		/*
+		 * DMABUF enqueue failed, but we already added the fence.
+		 * Signal the error through the fence completion mechanism.
+		 */
+		iio_buffer_signal_dmabuf_done(&fence->base, ret);
+	}
+
+	if (buffer->access->unlock_queue)
+		buffer->access->unlock_queue(buffer);
+
+	dma_fence_end_signalling(cookie);
+	dma_buf_put(dmabuf);
+
+	return ret;
+
+err_queue_unlock:
+	if (buffer->access->unlock_queue)
+		buffer->access->unlock_queue(buffer);
+err_resv_unlock:
+	dma_resv_unlock(dmabuf->resv);
+err_fence_put:
+	dma_fence_put(&fence->base);
+err_attachment_put:
+	iio_buffer_dmabuf_put(attach);
+err_dmabuf_put:
+	dma_buf_put(dmabuf);
+
+	return ret;
+}
+
+static void iio_buffer_cleanup(struct work_struct *work)
+{
+	struct iio_dma_fence *fence =
+		container_of(work, struct iio_dma_fence, work);
+	struct iio_dmabuf_priv *priv = fence->priv;
+	struct dma_buf_attachment *attach = priv->attach;
+
+	dma_fence_put(&fence->base);
+	iio_buffer_dmabuf_put(attach);
+}
+
+void iio_buffer_signal_dmabuf_done(struct dma_fence *fence, int ret)
+{
+	struct iio_dma_fence *iio_fence =
+		container_of(fence, struct iio_dma_fence, base);
+	bool cookie = dma_fence_begin_signalling();
+
+	/*
+	 * Get a reference to the fence, so that it's not freed as soon as
+	 * it's signaled.
+	 */
+	dma_fence_get(fence);
+
+	fence->error = ret;
+	dma_fence_signal(fence);
+	dma_fence_end_signalling(cookie);
+
+	/*
+	 * The fence will be unref'd in iio_buffer_cleanup.
+	 * It can't be done here, as the unref functions might try to lock the
+	 * resv object, which can deadlock.
+	 */
+	INIT_WORK(&iio_fence->work, iio_buffer_cleanup);
+	schedule_work(&iio_fence->work);
+}
+EXPORT_SYMBOL_GPL(iio_buffer_signal_dmabuf_done);
+
+static long iio_buffer_chrdev_ioctl(struct file *filp,
+				    unsigned int cmd, unsigned long arg)
+{
+	struct iio_dev_buffer_pair *ib = filp->private_data;
+	void __user *_arg = (void __user *)arg;
+	bool nonblock = filp->f_flags & O_NONBLOCK;
+
+	switch (cmd) {
+	case IIO_BUFFER_DMABUF_ATTACH_IOCTL:
+		return iio_buffer_attach_dmabuf(ib, _arg, nonblock);
+	case IIO_BUFFER_DMABUF_DETACH_IOCTL:
+		return iio_buffer_detach_dmabuf(ib, _arg, nonblock);
+	case IIO_BUFFER_DMABUF_ENQUEUE_IOCTL:
+		return iio_buffer_enqueue_dmabuf(ib, _arg, nonblock);
+	default:
+		return -EINVAL;
+	}
+}
+
 static const struct file_operations iio_buffer_chrdev_fileops = {
 	.owner = THIS_MODULE,
 	.llseek = noop_llseek,
 	.read = iio_buffer_read,
 	.write = iio_buffer_write,
+	.unlocked_ioctl = iio_buffer_chrdev_ioctl,
+	.compat_ioctl = compat_ptr_ioctl,
 	.poll = iio_buffer_poll,
 	.release = iio_buffer_chrdev_release,
 };
@@ -1994,6 +2455,7 @@ static void iio_buffer_release(struct kref *ref)
 {
 	struct iio_buffer *buffer = container_of(ref, struct iio_buffer, ref);
 
+	mutex_destroy(&buffer->dmabufs_mutex);
 	buffer->access->release(buffer);
 }
 
diff --git a/include/linux/iio/buffer_impl.h b/include/linux/iio/buffer_impl.h
index 89c3fd7c29ca..1a221c1d7736 100644
--- a/include/linux/iio/buffer_impl.h
+++ b/include/linux/iio/buffer_impl.h
@@ -9,8 +9,12 @@
 #include <uapi/linux/iio/buffer.h>
 #include <linux/iio/buffer.h>
 
+struct dma_buf_attachment;
+struct dma_fence;
 struct iio_dev;
+struct iio_dma_buffer_block;
 struct iio_buffer;
+struct sg_table;
 
 /**
  * INDIO_BUFFER_FLAG_FIXED_WATERMARK - Watermark level of the buffer can not be
@@ -39,6 +43,13 @@ struct iio_buffer;
  *                      device stops sampling. Calles are balanced with @enable.
  * @release:		called when the last reference to the buffer is dropped,
  *			should free all resources allocated by the buffer.
+ * @attach_dmabuf:	called from userspace via ioctl to attach one external
+ *			DMABUF.
+ * @detach_dmabuf:	called from userspace via ioctl to detach one previously
+ *			attached DMABUF.
+ * @enqueue_dmabuf:	called from userspace via ioctl to queue this DMABUF
+ *			object to this buffer. Requires a valid DMABUF fd, that
+ *			was previouly attached to this buffer.
  * @modes:		Supported operating modes by this buffer type
  * @flags:		A bitmask combination of INDIO_BUFFER_FLAG_*
  *
@@ -68,6 +79,17 @@ struct iio_buffer_access_funcs {
 
 	void (*release)(struct iio_buffer *buffer);
 
+	struct iio_dma_buffer_block * (*attach_dmabuf)(struct iio_buffer *buffer,
+						       struct dma_buf_attachment *attach);
+	void (*detach_dmabuf)(struct iio_buffer *buffer,
+			      struct iio_dma_buffer_block *block);
+	int (*enqueue_dmabuf)(struct iio_buffer *buffer,
+			      struct iio_dma_buffer_block *block,
+			      struct dma_fence *fence, struct sg_table *sgt,
+			      size_t size, bool cyclic);
+	void (*lock_queue)(struct iio_buffer *buffer);
+	void (*unlock_queue)(struct iio_buffer *buffer);
+
 	unsigned int modes;
 	unsigned int flags;
 };
@@ -136,6 +158,12 @@ struct iio_buffer {
 
 	/* @ref: Reference count of the buffer. */
 	struct kref ref;
+
+	/* @dmabufs: List of DMABUF attachments */
+	struct list_head dmabufs; /* P: dmabufs_mutex */
+
+	/* @dmabufs_mutex: Protects dmabufs */
+	struct mutex dmabufs_mutex;
 };
 
 /**
@@ -159,6 +187,8 @@ void iio_buffer_init(struct iio_buffer *buffer);
 struct iio_buffer *iio_buffer_get(struct iio_buffer *buffer);
 void iio_buffer_put(struct iio_buffer *buffer);
 
+void iio_buffer_signal_dmabuf_done(struct dma_fence *fence, int ret);
+
 #else /* CONFIG_IIO_BUFFER */
 
 static inline void iio_buffer_get(struct iio_buffer *buffer) {}
diff --git a/include/uapi/linux/iio/buffer.h b/include/uapi/linux/iio/buffer.h
index 13939032b3f6..c666aa95e532 100644
--- a/include/uapi/linux/iio/buffer.h
+++ b/include/uapi/linux/iio/buffer.h
@@ -5,6 +5,28 @@
 #ifndef _UAPI_IIO_BUFFER_H_
 #define _UAPI_IIO_BUFFER_H_
 
+#include <linux/types.h>
+
+/* Flags for iio_dmabuf.flags */
+#define IIO_BUFFER_DMABUF_CYCLIC		(1 << 0)
+#define IIO_BUFFER_DMABUF_SUPPORTED_FLAGS	0x00000001
+
+/**
+ * struct iio_dmabuf - Descriptor for a single IIO DMABUF object
+ * @fd:		file descriptor of the DMABUF object
+ * @flags:	one or more IIO_BUFFER_DMABUF_* flags
+ * @bytes_used:	number of bytes used in this DMABUF for the data transfer.
+ *		Should generally be set to the DMABUF's size.
+ */
+struct iio_dmabuf {
+	__u32 fd;
+	__u32 flags;
+	__u64 bytes_used;
+};
+
 #define IIO_BUFFER_GET_FD_IOCTL			_IOWR('i', 0x91, int)
+#define IIO_BUFFER_DMABUF_ATTACH_IOCTL		_IOW('i', 0x92, int)
+#define IIO_BUFFER_DMABUF_DETACH_IOCTL		_IOW('i', 0x93, int)
+#define IIO_BUFFER_DMABUF_ENQUEUE_IOCTL		_IOW('i', 0x94, struct iio_dmabuf)
 
 #endif /* _UAPI_IIO_BUFFER_H_ */
-- 
2.43.0

Re: [PATCH v10 3/6] iio: core: Add new DMABUF interface infrastructure

[Jonathan Cameron]

On Wed,  5 Jun 2024 13:08:42 +0200
Paul Cercueil <paul@crapouillou.net> wrote:

> Add the necessary infrastructure to the IIO core to support a new
> optional DMABUF based interface.
> 
> With this new interface, DMABUF objects (externally created) can be
> attached to a IIO buffer, and subsequently used for data transfer.
> 
> 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.
> 
> The userspace application can also memory-map the DMABUF objects, and
> access the sample data directly. The advantage of doing this vs. the
> read() interface is that it avoids an extra copy of the data between the
> kernel and userspace. This is particularly userful for high-speed
> devices which produce several megabytes or even gigabytes of data per
> second.
> 
> As part of the interface, 3 new IOCTLs have been added:
> 
> IIO_BUFFER_DMABUF_ATTACH_IOCTL(int fd):
>  Attach the DMABUF object identified by the given file descriptor to the
>  buffer.
> 
> IIO_BUFFER_DMABUF_DETACH_IOCTL(int fd):
>  Detach the DMABUF object identified by the given file descriptor from
>  the buffer. Note that closing the IIO buffer's file descriptor will
>  automatically detach all previously attached DMABUF objects.
> 
> IIO_BUFFER_DMABUF_ENQUEUE_IOCTL(struct iio_dmabuf *):
>  Request a data transfer to/from the given DMABUF object. Its file
>  descriptor, as well as the transfer size and flags are provided in the
>  "iio_dmabuf" structure.
> 
> These three IOCTLs have to be performed on the IIO buffer's file
> descriptor, obtained using the IIO_BUFFER_GET_FD_IOCTL() ioctl.
> 
> Signed-off-by: Paul Cercueil <paul@crapouillou.net>
> Signed-off-by: Nuno Sa <nuno.sa@analog.com>

Need a brief note on the sign off chain.
What is Nuno's role in this series as he's not sending the emails and not
marked with Co-developed-by 

I gave this a much more thorough look in earlier versions than I have today but
a few really minor things inline (that I might have fixed up whilst applying)
but looks like you'll be done a v11 for Randy's docs comments anyway :(

Jonathan


> diff --git a/drivers/iio/industrialio-buffer.c b/drivers/iio/industrialio-buffer.c
> index 0138b21b244f..c98c8ac83785 100644
> --- a/drivers/iio/industrialio-buffer.c
> +++ b/drivers/iio/industrialio-buffer.c

> +struct iio_dmabuf_priv {
> +	struct list_head entry;
> +	struct kref ref;
> +
> +	struct iio_buffer *buffer;
> +	struct iio_dma_buffer_block *block;
> +
> +	u64 context;
> +	spinlock_t lock;

Given you are going to have a v11, please add a comment to this lock
to say what data it is protecting. 

> +
> +	struct dma_buf_attachment *attach;
> +	struct sg_table *sgt;
> +	enum dma_data_direction dir;
> +	atomic_t seqno;
> +};


> diff --git a/include/linux/iio/buffer_impl.h b/include/linux/iio/buffer_impl.h
> index 89c3fd7c29ca..1a221c1d7736 100644
> --- a/include/linux/iio/buffer_impl.h
> +++ b/include/linux/iio/buffer_impl.h
> @@ -9,8 +9,12 @@
>  #include <uapi/linux/iio/buffer.h>
>  #include <linux/iio/buffer.h>
>  
> +struct dma_buf_attachment;
> +struct dma_fence;
>  struct iio_dev;
> +struct iio_dma_buffer_block;
>  struct iio_buffer;
> +struct sg_table;
>  
>  /**
>   * INDIO_BUFFER_FLAG_FIXED_WATERMARK - Watermark level of the buffer can not be
> @@ -39,6 +43,13 @@ struct iio_buffer;
>   *                      device stops sampling. Calles are balanced with @enable.
>   * @release:		called when the last reference to the buffer is dropped,
>   *			should free all resources allocated by the buffer.
> + * @attach_dmabuf:	called from userspace via ioctl to attach one external
> + *			DMABUF.
> + * @detach_dmabuf:	called from userspace via ioctl to detach one previously
> + *			attached DMABUF.
> + * @enqueue_dmabuf:	called from userspace via ioctl to queue this DMABUF
> + *			object to this buffer. Requires a valid DMABUF fd, that
> + *			was previouly attached to this buffer.

Missing docs for lock_queue() and unlock_queue()

Kernel-doc must be complete or bots are going to moan at us :(

>   * @modes:		Supported operating modes by this buffer type
>   * @flags:		A bitmask combination of INDIO_BUFFER_FLAG_*
>   *
> @@ -68,6 +79,17 @@ struct iio_buffer_access_funcs {
>  
>  	void (*release)(struct iio_buffer *buffer);
>  
> +	struct iio_dma_buffer_block * (*attach_dmabuf)(struct iio_buffer *buffer,
> +						       struct dma_buf_attachment *attach);
> +	void (*detach_dmabuf)(struct iio_buffer *buffer,
> +			      struct iio_dma_buffer_block *block);
> +	int (*enqueue_dmabuf)(struct iio_buffer *buffer,
> +			      struct iio_dma_buffer_block *block,
> +			      struct dma_fence *fence, struct sg_table *sgt,
> +			      size_t size, bool cyclic);
> +	void (*lock_queue)(struct iio_buffer *buffer);
> +	void (*unlock_queue)(struct iio_buffer *buffer);
> +

Re: [PATCH v10 3/6] iio: core: Add new DMABUF interface infrastructure

[Paul Cercueil]

Le dimanche 09 juin 2024 à 10:53 +0100, Jonathan Cameron a écrit :
> On Wed,  5 Jun 2024 13:08:42 +0200
> Paul Cercueil <paul@crapouillou.net> wrote:
> 
> > Add the necessary infrastructure to the IIO core to support a new
> > optional DMABUF based interface.
> > 
> > With this new interface, DMABUF objects (externally created) can be
> > attached to a IIO buffer, and subsequently used for data transfer.
> > 
> > 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.
> > 
> > The userspace application can also memory-map the DMABUF objects,
> > and
> > access the sample data directly. The advantage of doing this vs.
> > the
> > read() interface is that it avoids an extra copy of the data
> > between the
> > kernel and userspace. This is particularly userful for high-speed
> > devices which produce several megabytes or even gigabytes of data
> > per
> > second.
> > 
> > As part of the interface, 3 new IOCTLs have been added:
> > 
> > IIO_BUFFER_DMABUF_ATTACH_IOCTL(int fd):
> >  Attach the DMABUF object identified by the given file descriptor
> > to the
> >  buffer.
> > 
> > IIO_BUFFER_DMABUF_DETACH_IOCTL(int fd):
> >  Detach the DMABUF object identified by the given file descriptor
> > from
> >  the buffer. Note that closing the IIO buffer's file descriptor
> > will
> >  automatically detach all previously attached DMABUF objects.
> > 
> > IIO_BUFFER_DMABUF_ENQUEUE_IOCTL(struct iio_dmabuf *):
> >  Request a data transfer to/from the given DMABUF object. Its file
> >  descriptor, as well as the transfer size and flags are provided in
> > the
> >  "iio_dmabuf" structure.
> > 
> > These three IOCTLs have to be performed on the IIO buffer's file
> > descriptor, obtained using the IIO_BUFFER_GET_FD_IOCTL() ioctl.
> > 
> > Signed-off-by: Paul Cercueil <paul@crapouillou.net>
> > Signed-off-by: Nuno Sa <nuno.sa@analog.com>
> 
> Need a brief note on the sign off chain.
> What is Nuno's role in this series as he's not sending the emails and
> not
> marked with Co-developed-by 

That's a good question. I think he sent one revision of the patchset
(v7 or something like that) so he added his SoB.

(Nuno: you confirm?)

I'll add his Co-developed-by then.

Cheers,
-Paul

> I gave this a much more thorough look in earlier versions than I have
> today but
> a few really minor things inline (that I might have fixed up whilst
> applying)
> but looks like you'll be done a v11 for Randy's docs comments anyway
> :(
> 
> Jonathan
> 
> 
> > diff --git a/drivers/iio/industrialio-buffer.c
> > b/drivers/iio/industrialio-buffer.c
> > index 0138b21b244f..c98c8ac83785 100644
> > --- a/drivers/iio/industrialio-buffer.c
> > +++ b/drivers/iio/industrialio-buffer.c
> 
> > +struct iio_dmabuf_priv {
> > +	struct list_head entry;
> > +	struct kref ref;
> > +
> > +	struct iio_buffer *buffer;
> > +	struct iio_dma_buffer_block *block;
> > +
> > +	u64 context;
> > +	spinlock_t lock;
> 
> Given you are going to have a v11, please add a comment to this lock
> to say what data it is protecting. 
> 
> > +
> > +	struct dma_buf_attachment *attach;
> > +	struct sg_table *sgt;
> > +	enum dma_data_direction dir;
> > +	atomic_t seqno;
> > +};
> 
> 
> > diff --git a/include/linux/iio/buffer_impl.h
> > b/include/linux/iio/buffer_impl.h
> > index 89c3fd7c29ca..1a221c1d7736 100644
> > --- a/include/linux/iio/buffer_impl.h
> > +++ b/include/linux/iio/buffer_impl.h
> > @@ -9,8 +9,12 @@
> >  #include <uapi/linux/iio/buffer.h>
> >  #include <linux/iio/buffer.h>
> >  
> > +struct dma_buf_attachment;
> > +struct dma_fence;
> >  struct iio_dev;
> > +struct iio_dma_buffer_block;
> >  struct iio_buffer;
> > +struct sg_table;
> >  
> >  /**
> >   * INDIO_BUFFER_FLAG_FIXED_WATERMARK - Watermark level of the
> > buffer can not be
> > @@ -39,6 +43,13 @@ struct iio_buffer;
> >   *                      device stops sampling. Calles are balanced
> > with @enable.
> >   * @release:		called when the last reference to the
> > buffer is dropped,
> >   *			should free all resources allocated by the
> > buffer.
> > + * @attach_dmabuf:	called from userspace via ioctl to attach
> > one external
> > + *			DMABUF.
> > + * @detach_dmabuf:	called from userspace via ioctl to detach
> > one previously
> > + *			attached DMABUF.
> > + * @enqueue_dmabuf:	called from userspace via ioctl to queue
> > this DMABUF
> > + *			object to this buffer. Requires a valid
> > DMABUF fd, that
> > + *			was previouly attached to this buffer.
> 
> Missing docs for lock_queue() and unlock_queue()
> 
> Kernel-doc must be complete or bots are going to moan at us :(
> 
> >   * @modes:		Supported operating modes by this buffer
> > type
> >   * @flags:		A bitmask combination of
> > INDIO_BUFFER_FLAG_*
> >   *
> > @@ -68,6 +79,17 @@ struct iio_buffer_access_funcs {
> >  
> >  	void (*release)(struct iio_buffer *buffer);
> >  
> > +	struct iio_dma_buffer_block * (*attach_dmabuf)(struct
> > iio_buffer *buffer,
> > +						       struct
> > dma_buf_attachment *attach);
> > +	void (*detach_dmabuf)(struct iio_buffer *buffer,
> > +			      struct iio_dma_buffer_block *block);
> > +	int (*enqueue_dmabuf)(struct iio_buffer *buffer,
> > +			      struct iio_dma_buffer_block *block,
> > +			      struct dma_fence *fence, struct
> > sg_table *sgt,
> > +			      size_t size, bool cyclic);
> > +	void (*lock_queue)(struct iio_buffer *buffer);
> > +	void (*unlock_queue)(struct iio_buffer *buffer);
> > +
> 
> 

Re: [PATCH v10 3/6] iio: core: Add new DMABUF interface infrastructure

[Nuno Sá]

On Sat, 2024-06-15 at 13:07 +0200, Paul Cercueil wrote:
> Le dimanche 09 juin 2024 à 10:53 +0100, Jonathan Cameron a écrit :
> > On Wed,  5 Jun 2024 13:08:42 +0200
> > Paul Cercueil <paul@crapouillou.net> wrote:
> > 
> > > Add the necessary infrastructure to the IIO core to support a new
> > > optional DMABUF based interface.
> > > 
> > > With this new interface, DMABUF objects (externally created) can be
> > > attached to a IIO buffer, and subsequently used for data transfer.
> > > 
> > > 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.
> > > 
> > > The userspace application can also memory-map the DMABUF objects,
> > > and
> > > access the sample data directly. The advantage of doing this vs.
> > > the
> > > read() interface is that it avoids an extra copy of the data
> > > between the
> > > kernel and userspace. This is particularly userful for high-speed
> > > devices which produce several megabytes or even gigabytes of data
> > > per
> > > second.
> > > 
> > > As part of the interface, 3 new IOCTLs have been added:
> > > 
> > > IIO_BUFFER_DMABUF_ATTACH_IOCTL(int fd):
> > >  Attach the DMABUF object identified by the given file descriptor
> > > to the
> > >  buffer.
> > > 
> > > IIO_BUFFER_DMABUF_DETACH_IOCTL(int fd):
> > >  Detach the DMABUF object identified by the given file descriptor
> > > from
> > >  the buffer. Note that closing the IIO buffer's file descriptor
> > > will
> > >  automatically detach all previously attached DMABUF objects.
> > > 
> > > IIO_BUFFER_DMABUF_ENQUEUE_IOCTL(struct iio_dmabuf *):
> > >  Request a data transfer to/from the given DMABUF object. Its file
> > >  descriptor, as well as the transfer size and flags are provided in
> > > the
> > >  "iio_dmabuf" structure.
> > > 
> > > These three IOCTLs have to be performed on the IIO buffer's file
> > > descriptor, obtained using the IIO_BUFFER_GET_FD_IOCTL() ioctl.
> > > 
> > > Signed-off-by: Paul Cercueil <paul@crapouillou.net>
> > > Signed-off-by: Nuno Sa <nuno.sa@analog.com>
> > 
> > Need a brief note on the sign off chain.
> > What is Nuno's role in this series as he's not sending the emails and
> > not
> > marked with Co-developed-by 
> 
> That's a good question. I think he sent one revision of the patchset
> (v7 or something like that) so he added his SoB.
> 
> (Nuno: you confirm?)

exactly...

> 
> I'll add his Co-developed-by then.

Not sure if that is really deserved :)... Maybe just remove my tag.

- Nuno Sá

Re: [PATCH v10 3/6] iio: core: Add new DMABUF interface infrastructure

[Markus Elfring]

…
> +++ b/drivers/iio/industrialio-buffer.c
…
>  static int iio_buffer_chrdev_release(struct inode *inode, struct file *filep)
>  {
…
>  	wake_up(&buffer->pollq);
>
> +	mutex_lock(&buffer->dmabufs_mutex);
> +
> +	/* Close all attached DMABUFs */
…
> +	mutex_unlock(&buffer->dmabufs_mutex);
> +
>  	kfree(ib);
…

Would you become interested to apply a statement like “guard(mutex)(&buffer->dmabufs_mutex);”?
https://elixir.bootlin.com/linux/v6.10-rc3/source/include/linux/mutex.h#L196

Regards,
Markus

Re: [PATCH v10 3/6] iio: core: Add new DMABUF interface infrastructure

[Paul Cercueil]

Hi Markus,

Le lundi 17 juin 2024 à 08:56 +0200, Markus Elfring a écrit :
> …
> > +++ b/drivers/iio/industrialio-buffer.c
> …
> >  static int iio_buffer_chrdev_release(struct inode *inode, struct
> > file *filep)
> >  {
> …
> >  	wake_up(&buffer->pollq);
> > 
> > +	mutex_lock(&buffer->dmabufs_mutex);
> > +
> > +	/* Close all attached DMABUFs */
> …
> > +	mutex_unlock(&buffer->dmabufs_mutex);
> > +
> >  	kfree(ib);
> …
> 
> Would you become interested to apply a statement like
> “guard(mutex)(&buffer->dmabufs_mutex);”?
> https://elixir.bootlin.com/linux/v6.10-rc3/source/include/linux/mutex.h#L196

I'll update the patch to use it.

Cheers,
-Paul

[PATCH v10 4/6] iio: buffer-dma: Enable support for DMABUFs

[Paul Cercueil]

Implement iio_dma_buffer_attach_dmabuf(), iio_dma_buffer_detach_dmabuf()
and iio_dma_buffer_transfer_dmabuf(), which can then be used by the IIO
DMA buffer implementations.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Nuno Sa <nuno.sa@analog.com>

---
v3: Update code to provide the functions that will be used as callbacks
    for the new IOCTLs.

v6: - Update iio_dma_buffer_enqueue_dmabuf() to take a dma_fence pointer
    - Pass that dma_fence pointer along to
      iio_buffer_signal_dmabuf_done()
    - Add iio_dma_buffer_lock_queue() / iio_dma_buffer_unlock_queue()
    - Do not lock the queue in iio_dma_buffer_enqueue_dmabuf().
      The caller will ensure that it has been locked already.
    - Replace "int += bool;" by "if (bool) int++;"
    - Use dma_fence_begin/end_signalling in the dma_fence critical
      sections
    - Use one "num_dmabufs" fields instead of one "num_blocks" and one
      "num_fileio_blocks". Make it an atomic_t, which makes it possible
      to decrement it atomically in iio_buffer_block_release() without
      having to lock the queue mutex; and in turn, it means that we
      don't need to use iio_buffer_block_put_atomic() everywhere to
      avoid locking the queue mutex twice.
    - Use cleanup.h guard(mutex) when possible
    - Explicitely list all states in the switch in
      iio_dma_can_enqueue_block()
    - Rename iio_dma_buffer_fileio_mode() to
      iio_dma_buffer_can_use_fileio(), and add a comment explaining why
      it cannot race vs. DMABUF.
---
 drivers/iio/buffer/industrialio-buffer-dma.c | 180 +++++++++++++++++--
 include/linux/iio/buffer-dma.h               |  31 ++++
 2 files changed, 200 insertions(+), 11 deletions(-)

diff --git a/drivers/iio/buffer/industrialio-buffer-dma.c b/drivers/iio/buffer/industrialio-buffer-dma.c
index 13b1a858969e..21d2feaee923 100644
--- a/drivers/iio/buffer/industrialio-buffer-dma.c
+++ b/drivers/iio/buffer/industrialio-buffer-dma.c
@@ -4,6 +4,8 @@
  *  Author: Lars-Peter Clausen <lars@metafoo.de>
  */
 
+#include <linux/atomic.h>
+#include <linux/cleanup.h>
 #include <linux/slab.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
@@ -14,6 +16,8 @@
 #include <linux/poll.h>
 #include <linux/iio/buffer_impl.h>
 #include <linux/iio/buffer-dma.h>
+#include <linux/dma-buf.h>
+#include <linux/dma-fence.h>
 #include <linux/dma-mapping.h>
 #include <linux/sizes.h>
 
@@ -94,13 +98,18 @@ static void iio_buffer_block_release(struct kref *kref)
 {
 	struct iio_dma_buffer_block *block = container_of(kref,
 		struct iio_dma_buffer_block, kref);
+	struct iio_dma_buffer_queue *queue = block->queue;
 
-	WARN_ON(block->state != IIO_BLOCK_STATE_DEAD);
+	WARN_ON(block->fileio && block->state != IIO_BLOCK_STATE_DEAD);
 
-	dma_free_coherent(block->queue->dev, PAGE_ALIGN(block->size),
-					block->vaddr, block->phys_addr);
+	if (block->fileio) {
+		dma_free_coherent(queue->dev, PAGE_ALIGN(block->size),
+				  block->vaddr, block->phys_addr);
+	} else {
+		atomic_dec(&queue->num_dmabufs);
+	}
 
-	iio_buffer_put(&block->queue->buffer);
+	iio_buffer_put(&queue->buffer);
 	kfree(block);
 }
 
@@ -163,7 +172,7 @@ static struct iio_dma_buffer_queue *iio_buffer_to_queue(struct iio_buffer *buf)
 }
 
 static struct iio_dma_buffer_block *iio_dma_buffer_alloc_block(
-	struct iio_dma_buffer_queue *queue, size_t size)
+	struct iio_dma_buffer_queue *queue, size_t size, bool fileio)
 {
 	struct iio_dma_buffer_block *block;
 
@@ -171,13 +180,16 @@ static struct iio_dma_buffer_block *iio_dma_buffer_alloc_block(
 	if (!block)
 		return NULL;
 
-	block->vaddr = dma_alloc_coherent(queue->dev, PAGE_ALIGN(size),
-		&block->phys_addr, GFP_KERNEL);
-	if (!block->vaddr) {
-		kfree(block);
-		return NULL;
+	if (fileio) {
+		block->vaddr = dma_alloc_coherent(queue->dev, PAGE_ALIGN(size),
+						  &block->phys_addr, GFP_KERNEL);
+		if (!block->vaddr) {
+			kfree(block);
+			return NULL;
+		}
 	}
 
+	block->fileio = fileio;
 	block->size = size;
 	block->state = IIO_BLOCK_STATE_DONE;
 	block->queue = queue;
@@ -186,6 +198,9 @@ static struct iio_dma_buffer_block *iio_dma_buffer_alloc_block(
 
 	iio_buffer_get(&queue->buffer);
 
+	if (!fileio)
+		atomic_inc(&queue->num_dmabufs);
+
 	return block;
 }
 
@@ -218,13 +233,20 @@ void iio_dma_buffer_block_done(struct iio_dma_buffer_block *block)
 {
 	struct iio_dma_buffer_queue *queue = block->queue;
 	unsigned long flags;
+	bool cookie;
+
+	cookie = dma_fence_begin_signalling();
 
 	spin_lock_irqsave(&queue->list_lock, flags);
 	_iio_dma_buffer_block_done(block);
 	spin_unlock_irqrestore(&queue->list_lock, flags);
 
+	if (!block->fileio)
+		iio_buffer_signal_dmabuf_done(block->fence, 0);
+
 	iio_buffer_block_put_atomic(block);
 	iio_dma_buffer_queue_wake(queue);
+	dma_fence_end_signalling(cookie);
 }
 EXPORT_SYMBOL_GPL(iio_dma_buffer_block_done);
 
@@ -243,17 +265,27 @@ void iio_dma_buffer_block_list_abort(struct iio_dma_buffer_queue *queue,
 {
 	struct iio_dma_buffer_block *block, *_block;
 	unsigned long flags;
+	bool cookie;
+
+	cookie = dma_fence_begin_signalling();
 
 	spin_lock_irqsave(&queue->list_lock, flags);
 	list_for_each_entry_safe(block, _block, list, head) {
 		list_del(&block->head);
 		block->bytes_used = 0;
 		_iio_dma_buffer_block_done(block);
+
+		if (!block->fileio)
+			iio_buffer_signal_dmabuf_done(block->fence, -EINTR);
 		iio_buffer_block_put_atomic(block);
 	}
 	spin_unlock_irqrestore(&queue->list_lock, flags);
 
+	if (queue->fileio.enabled)
+		queue->fileio.enabled = false;
+
 	iio_dma_buffer_queue_wake(queue);
+	dma_fence_end_signalling(cookie);
 }
 EXPORT_SYMBOL_GPL(iio_dma_buffer_block_list_abort);
 
@@ -273,6 +305,16 @@ static bool iio_dma_block_reusable(struct iio_dma_buffer_block *block)
 	}
 }
 
+static bool iio_dma_buffer_can_use_fileio(struct iio_dma_buffer_queue *queue)
+{
+	/*
+	 * Note that queue->num_dmabufs cannot increase while the queue is
+	 * locked, it can only decrease, so it does not race against
+	 * iio_dma_buffer_alloc_block().
+	 */
+	return queue->fileio.enabled || !atomic_read(&queue->num_dmabufs);
+}
+
 /**
  * iio_dma_buffer_request_update() - DMA buffer request_update callback
  * @buffer: The buffer which to request an update
@@ -299,6 +341,12 @@ int iio_dma_buffer_request_update(struct iio_buffer *buffer)
 
 	mutex_lock(&queue->lock);
 
+	queue->fileio.enabled = iio_dma_buffer_can_use_fileio(queue);
+
+	/* If DMABUFs were created, disable fileio interface */
+	if (!queue->fileio.enabled)
+		goto out_unlock;
+
 	/* Allocations are page aligned */
 	if (PAGE_ALIGN(queue->fileio.block_size) == PAGE_ALIGN(size))
 		try_reuse = true;
@@ -339,7 +387,7 @@ int iio_dma_buffer_request_update(struct iio_buffer *buffer)
 		}
 
 		if (!block) {
-			block = iio_dma_buffer_alloc_block(queue, size);
+			block = iio_dma_buffer_alloc_block(queue, size, true);
 			if (!block) {
 				ret = -ENOMEM;
 				goto out_unlock;
@@ -412,8 +460,12 @@ static void iio_dma_buffer_submit_block(struct iio_dma_buffer_queue *queue,
 
 	block->state = IIO_BLOCK_STATE_ACTIVE;
 	iio_buffer_block_get(block);
+
 	ret = queue->ops->submit(queue, block);
 	if (ret) {
+		if (!block->fileio)
+			iio_buffer_signal_dmabuf_done(block->fence, ret);
+
 		/*
 		 * This is a bit of a problem and there is not much we can do
 		 * other then wait for the buffer to be disabled and re-enabled
@@ -646,6 +698,112 @@ size_t iio_dma_buffer_usage(struct iio_buffer *buf)
 }
 EXPORT_SYMBOL_GPL(iio_dma_buffer_usage);
 
+struct iio_dma_buffer_block *
+iio_dma_buffer_attach_dmabuf(struct iio_buffer *buffer,
+			     struct dma_buf_attachment *attach)
+{
+	struct iio_dma_buffer_queue *queue = iio_buffer_to_queue(buffer);
+	struct iio_dma_buffer_block *block;
+
+	guard(mutex)(&queue->lock);
+
+	/*
+	 * If the buffer is enabled and in fileio mode new blocks can't be
+	 * allocated.
+	 */
+	if (queue->fileio.enabled)
+		return ERR_PTR(-EBUSY);
+
+	block = iio_dma_buffer_alloc_block(queue, attach->dmabuf->size, false);
+	if (!block)
+		return ERR_PTR(-ENOMEM);
+
+	block->attach = attach;
+
+	/* Free memory that might be in use for fileio mode */
+	iio_dma_buffer_fileio_free(queue);
+
+	return block;
+}
+EXPORT_SYMBOL_GPL(iio_dma_buffer_attach_dmabuf);
+
+void iio_dma_buffer_detach_dmabuf(struct iio_buffer *buffer,
+				  struct iio_dma_buffer_block *block)
+{
+	block->state = IIO_BLOCK_STATE_DEAD;
+	iio_buffer_block_put_atomic(block);
+}
+EXPORT_SYMBOL_GPL(iio_dma_buffer_detach_dmabuf);
+
+static int iio_dma_can_enqueue_block(struct iio_dma_buffer_block *block)
+{
+	struct iio_dma_buffer_queue *queue = block->queue;
+
+	/* If in fileio mode buffers can't be enqueued. */
+	if (queue->fileio.enabled)
+		return -EBUSY;
+
+	switch (block->state) {
+	case IIO_BLOCK_STATE_QUEUED:
+		return -EPERM;
+	case IIO_BLOCK_STATE_ACTIVE:
+	case IIO_BLOCK_STATE_DEAD:
+		return -EBUSY;
+	case IIO_BLOCK_STATE_DONE:
+		break;
+	}
+
+	return 0;
+}
+
+int iio_dma_buffer_enqueue_dmabuf(struct iio_buffer *buffer,
+				  struct iio_dma_buffer_block *block,
+				  struct dma_fence *fence,
+				  struct sg_table *sgt,
+				  size_t size, bool cyclic)
+{
+	struct iio_dma_buffer_queue *queue = iio_buffer_to_queue(buffer);
+	bool cookie;
+	int ret;
+
+	WARN_ON(!mutex_is_locked(&queue->lock));
+
+	cookie = dma_fence_begin_signalling();
+
+	ret = iio_dma_can_enqueue_block(block);
+	if (ret < 0)
+		goto out_end_signalling;
+
+	block->bytes_used = size;
+	block->cyclic = cyclic;
+	block->sg_table = sgt;
+	block->fence = fence;
+
+	iio_dma_buffer_enqueue(queue, block);
+
+out_end_signalling:
+	dma_fence_end_signalling(cookie);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(iio_dma_buffer_enqueue_dmabuf);
+
+void iio_dma_buffer_lock_queue(struct iio_buffer *buffer)
+{
+	struct iio_dma_buffer_queue *queue = iio_buffer_to_queue(buffer);
+
+	mutex_lock(&queue->lock);
+}
+EXPORT_SYMBOL_GPL(iio_dma_buffer_lock_queue);
+
+void iio_dma_buffer_unlock_queue(struct iio_buffer *buffer)
+{
+	struct iio_dma_buffer_queue *queue = iio_buffer_to_queue(buffer);
+
+	mutex_unlock(&queue->lock);
+}
+EXPORT_SYMBOL_GPL(iio_dma_buffer_unlock_queue);
+
 /**
  * iio_dma_buffer_set_bytes_per_datum() - DMA buffer set_bytes_per_datum callback
  * @buffer: Buffer to set the bytes-per-datum for
diff --git a/include/linux/iio/buffer-dma.h b/include/linux/iio/buffer-dma.h
index 6e27e47077d5..e54158e53fd6 100644
--- a/include/linux/iio/buffer-dma.h
+++ b/include/linux/iio/buffer-dma.h
@@ -7,6 +7,7 @@
 #ifndef __INDUSTRIALIO_DMA_BUFFER_H__
 #define __INDUSTRIALIO_DMA_BUFFER_H__
 
+#include <linux/atomic.h>
 #include <linux/list.h>
 #include <linux/kref.h>
 #include <linux/spinlock.h>
@@ -16,6 +17,9 @@
 struct iio_dma_buffer_queue;
 struct iio_dma_buffer_ops;
 struct device;
+struct dma_buf_attachment;
+struct dma_fence;
+struct sg_table;
 
 /**
  * enum iio_block_state - State of a struct iio_dma_buffer_block
@@ -41,6 +45,8 @@ enum iio_block_state {
  * @queue: Parent DMA buffer queue
  * @kref: kref used to manage the lifetime of block
  * @state: Current state of the block
+ * @cyclic: True if this is a cyclic buffer
+ * @fileio: True if this buffer is used for fileio mode
  */
 struct iio_dma_buffer_block {
 	/* May only be accessed by the owner of the block */
@@ -63,6 +69,14 @@ struct iio_dma_buffer_block {
 	 * queue->list_lock if the block is not owned by the core.
 	 */
 	enum iio_block_state state;
+
+	bool cyclic;
+	bool fileio;
+
+	struct dma_buf_attachment *attach;
+	struct sg_table *sg_table;
+
+	struct dma_fence *fence;
 };
 
 /**
@@ -72,6 +86,7 @@ struct iio_dma_buffer_block {
  * @pos: Read offset in the active block
  * @block_size: Size of each block
  * @next_dequeue: index of next block that will be dequeued
+ * @enabled: Whether the buffer is operating in fileio mode
  */
 struct iio_dma_buffer_queue_fileio {
 	struct iio_dma_buffer_block *blocks[2];
@@ -80,6 +95,7 @@ struct iio_dma_buffer_queue_fileio {
 	size_t block_size;
 
 	unsigned int next_dequeue;
+	bool enabled;
 };
 
 /**
@@ -95,6 +111,7 @@ struct iio_dma_buffer_queue_fileio {
  *   the DMA controller
  * @incoming: List of buffers on the incoming queue
  * @active: Whether the buffer is currently active
+ * @num_dmabufs: Total number of DMABUFs attached to this queue
  * @fileio: FileIO state
  */
 struct iio_dma_buffer_queue {
@@ -107,6 +124,7 @@ struct iio_dma_buffer_queue {
 	struct list_head incoming;
 
 	bool active;
+	atomic_t num_dmabufs;
 
 	struct iio_dma_buffer_queue_fileio fileio;
 };
@@ -144,4 +162,17 @@ int iio_dma_buffer_init(struct iio_dma_buffer_queue *queue,
 void iio_dma_buffer_exit(struct iio_dma_buffer_queue *queue);
 void iio_dma_buffer_release(struct iio_dma_buffer_queue *queue);
 
+struct iio_dma_buffer_block *
+iio_dma_buffer_attach_dmabuf(struct iio_buffer *buffer,
+			     struct dma_buf_attachment *attach);
+void iio_dma_buffer_detach_dmabuf(struct iio_buffer *buffer,
+				  struct iio_dma_buffer_block *block);
+int iio_dma_buffer_enqueue_dmabuf(struct iio_buffer *buffer,
+				  struct iio_dma_buffer_block *block,
+				  struct dma_fence *fence,
+				  struct sg_table *sgt,
+				  size_t size, bool cyclic);
+void iio_dma_buffer_lock_queue(struct iio_buffer *buffer);
+void iio_dma_buffer_unlock_queue(struct iio_buffer *buffer);
+
 #endif
-- 
2.43.0

Re: [PATCH v10 4/6] iio: buffer-dma: Enable support for DMABUFs

[Jonathan Cameron]

On Wed,  5 Jun 2024 13:08:43 +0200
Paul Cercueil <paul@crapouillou.net> wrote:

> Implement iio_dma_buffer_attach_dmabuf(), iio_dma_buffer_detach_dmabuf()
> and iio_dma_buffer_transfer_dmabuf(), which can then be used by the IIO
> DMA buffer implementations.
> 
> Signed-off-by: Paul Cercueil <paul@crapouillou.net>
> Signed-off-by: Nuno Sa <nuno.sa@analog.com>
> 
Same thing on SoB.
Also another missing structure field related docs comment inline.

> diff --git a/include/linux/iio/buffer-dma.h b/include/linux/iio/buffer-dma.h
> index 6e27e47077d5..e54158e53fd6 100644
> --- a/include/linux/iio/buffer-dma.h
> +++ b/include/linux/iio/buffer-dma.h
> @@ -7,6 +7,7 @@
>  #ifndef __INDUSTRIALIO_DMA_BUFFER_H__
>  #define __INDUSTRIALIO_DMA_BUFFER_H__
>  
> +#include <linux/atomic.h>
>  #include <linux/list.h>
>  #include <linux/kref.h>
>  #include <linux/spinlock.h>
> @@ -16,6 +17,9 @@
>  struct iio_dma_buffer_queue;
>  struct iio_dma_buffer_ops;
>  struct device;
> +struct dma_buf_attachment;
> +struct dma_fence;
> +struct sg_table;
>  
>  /**
>   * enum iio_block_state - State of a struct iio_dma_buffer_block
> @@ -41,6 +45,8 @@ enum iio_block_state {
>   * @queue: Parent DMA buffer queue
>   * @kref: kref used to manage the lifetime of block
>   * @state: Current state of the block
> + * @cyclic: True if this is a cyclic buffer
> + * @fileio: True if this buffer is used for fileio mode

kernel doc needs to be complete. So missing attach, sg_table and fence.

>   */
>  struct iio_dma_buffer_block {
>  	/* May only be accessed by the owner of the block */
> @@ -63,6 +69,14 @@ struct iio_dma_buffer_block {
>  	 * queue->list_lock if the block is not owned by the core.
>  	 */
>  	enum iio_block_state state;
> +
> +	bool cyclic;
> +	bool fileio;
> +
> +	struct dma_buf_attachment *attach;
> +	struct sg_table *sg_table;
> +
> +	struct dma_fence *fence;
>  };

[PATCH v10 5/6] iio: buffer-dmaengine: Support new DMABUF based userspace API

[Paul Cercueil]

Use the functions provided by the buffer-dma core to implement the
DMABUF userspace API in the buffer-dmaengine IIO buffer implementation.

Since we want to be able to transfer an arbitrary number of bytes and
not necesarily the full DMABUF, the associated scatterlist is converted
to an array of DMA addresses + lengths, which is then passed to
dmaengine_prep_slave_dma_array().

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Nuno Sa <nuno.sa@analog.com>

---
v3: Use the new dmaengine_prep_slave_dma_array(), and adapt the code to
    work with the new functions introduced in industrialio-buffer-dma.c.

v5: - Use the new dmaengine_prep_slave_dma_vec().
    - Restrict to input buffers, since output buffers are not yet
      supported by IIO buffers.

v6: - Populate .lock_queue / .unlock_queue callbacks
    - Switch to atomic memory allocations in .submit_queue, because of
      the dma_fence critical section
    - Make sure that the size of the scatterlist is enough

v7: Adapted patch for the changes made in patch 1.

v10:
  - Remove extra flags parameter to dmaengine_prep_peripheral_dma_vec()
  - Add support for TX transfers
---
 .../buffer/industrialio-buffer-dmaengine.c    | 62 ++++++++++++++++---
 1 file changed, 53 insertions(+), 9 deletions(-)

diff --git a/drivers/iio/buffer/industrialio-buffer-dmaengine.c b/drivers/iio/buffer/industrialio-buffer-dmaengine.c
index 918f6f8d65b6..12aa1412dfa0 100644
--- a/drivers/iio/buffer/industrialio-buffer-dmaengine.c
+++ b/drivers/iio/buffer/industrialio-buffer-dmaengine.c
@@ -65,25 +65,62 @@ static int iio_dmaengine_buffer_submit_block(struct iio_dma_buffer_queue *queue,
 		iio_buffer_to_dmaengine_buffer(&queue->buffer);
 	struct dma_async_tx_descriptor *desc;
 	enum dma_transfer_direction dma_dir;
+	struct scatterlist *sgl;
+	struct dma_vec *vecs;
 	size_t max_size;
 	dma_cookie_t cookie;
+	size_t len_total;
+	unsigned int i;
+	int nents;
 
 	max_size = min(block->size, dmaengine_buffer->max_size);
 	max_size = round_down(max_size, dmaengine_buffer->align);
 
-	if (queue->buffer.direction == IIO_BUFFER_DIRECTION_IN) {
-		block->bytes_used = max_size;
+	if (queue->buffer.direction == IIO_BUFFER_DIRECTION_IN)
 		dma_dir = DMA_DEV_TO_MEM;
-	} else {
+	else
 		dma_dir = DMA_MEM_TO_DEV;
-	}
 
-	if (!block->bytes_used || block->bytes_used > max_size)
-		return -EINVAL;
+	if (block->sg_table) {
+		sgl = block->sg_table->sgl;
+		nents = sg_nents_for_len(sgl, block->bytes_used);
+		if (nents < 0)
+			return nents;
+
+		vecs = kmalloc_array(nents, sizeof(*vecs), GFP_ATOMIC);
+		if (!vecs)
+			return -ENOMEM;
+
+		len_total = block->bytes_used;
+
+		for (i = 0; i < nents; i++) {
+			vecs[i].addr = sg_dma_address(sgl);
+			vecs[i].len = min(sg_dma_len(sgl), len_total);
+			len_total -= vecs[i].len;
+
+			sgl = sg_next(sgl);
+		}
 
-	desc = dmaengine_prep_slave_single(dmaengine_buffer->chan,
-		block->phys_addr, block->bytes_used, dma_dir,
-		DMA_PREP_INTERRUPT);
+		desc = dmaengine_prep_peripheral_dma_vec(dmaengine_buffer->chan,
+							 vecs, nents, dma_dir,
+							 DMA_PREP_INTERRUPT);
+		kfree(vecs);
+	} else {
+		max_size = min(block->size, dmaengine_buffer->max_size);
+		max_size = round_down(max_size, dmaengine_buffer->align);
+
+		if (queue->buffer.direction == IIO_BUFFER_DIRECTION_IN)
+			block->bytes_used = max_size;
+
+		if (!block->bytes_used || block->bytes_used > max_size)
+			return -EINVAL;
+
+		desc = dmaengine_prep_slave_single(dmaengine_buffer->chan,
+						   block->phys_addr,
+						   block->bytes_used,
+						   dma_dir,
+						   DMA_PREP_INTERRUPT);
+	}
 	if (!desc)
 		return -ENOMEM;
 
@@ -133,6 +170,13 @@ static const struct iio_buffer_access_funcs iio_dmaengine_buffer_ops = {
 	.space_available = iio_dma_buffer_usage,
 	.release = iio_dmaengine_buffer_release,
 
+	.enqueue_dmabuf = iio_dma_buffer_enqueue_dmabuf,
+	.attach_dmabuf = iio_dma_buffer_attach_dmabuf,
+	.detach_dmabuf = iio_dma_buffer_detach_dmabuf,
+
+	.lock_queue = iio_dma_buffer_lock_queue,
+	.unlock_queue = iio_dma_buffer_unlock_queue,
+
 	.modes = INDIO_BUFFER_HARDWARE,
 	.flags = INDIO_BUFFER_FLAG_FIXED_WATERMARK,
 };
-- 
2.43.0

[PATCH v10 6/6] Documentation: iio: Document high-speed DMABUF based API

[Paul Cercueil]

Document the new DMABUF based API.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Nuno Sa <nuno.sa@analog.com>

---
v2: - Explicitly state that the new interface is optional and is
      not implemented by all drivers.
    - The IOCTLs can now only be called on the buffer FD returned by
      IIO_BUFFER_GET_FD_IOCTL.
    - Move the page up a bit in the index since it is core stuff and not
      driver-specific.

v3: Update the documentation to reflect the new API.

v5: Use description lists for the documentation of the three new IOCTLs
    instead of abusing subsections.

v8: Renamed dmabuf_api.rst -> iio_dmabuf_api.rst, and updated index.rst
    whose format changed in iio/togreg.
---
 Documentation/iio/iio_dmabuf_api.rst | 54 ++++++++++++++++++++++++++++
 Documentation/iio/index.rst          |  1 +
 2 files changed, 55 insertions(+)
 create mode 100644 Documentation/iio/iio_dmabuf_api.rst

diff --git a/Documentation/iio/iio_dmabuf_api.rst b/Documentation/iio/iio_dmabuf_api.rst
new file mode 100644
index 000000000000..1cd6cd51a582
--- /dev/null
+++ b/Documentation/iio/iio_dmabuf_api.rst
@@ -0,0 +1,54 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===================================
+High-speed DMABUF interface for IIO
+===================================
+
+1. Overview
+===========
+
+The Industrial I/O subsystem supports access to buffers through a
+file-based interface, with read() and write() access calls through the
+IIO device's dev node.
+
+It additionally supports a DMABUF based interface, where the userspace
+can attach DMABUF objects (externally created) to a IIO buffer, 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.
+
+The userspace application can also memory-map the DMABUF objects, and
+access the sample data directly. The advantage of doing this vs. the
+read() interface is that it avoids an extra copy of the data between the
+kernel and userspace. This is particularly useful for high-speed devices
+which produce several megabytes or even gigabytes of data per second.
+It does however increase the userspace-kernelspace synchronization
+overhead, as the DMA_BUF_SYNC_START and DMA_BUF_SYNC_END IOCTLs have to
+be used for data integrity.
+
+2. User API
+===========
+
+As part of this interface, three new IOCTLs have been added. These three
+IOCTLs have to be performed on the IIO buffer's file descriptor,
+obtained using the IIO_BUFFER_GET_FD_IOCTL() ioctl.
+
+  ``IIO_BUFFER_DMABUF_ATTACH_IOCTL(int)``
+    Attach the DMABUF object, identified by its file descriptor, to the
+    IIO buffer. Returns zero on success, and a negative errno value on
+    error.
+
+  ``IIO_BUFFER_DMABUF_DETACH_IOCTL(int)``
+    Detach the given DMABUF object, identified by its file descriptor,
+    from the IIO buffer. Returns zero on success, and a negative errno
+    value on error.
+
+    Note that closing the IIO buffer's file descriptor will
+    automatically detach all previously attached DMABUF objects.
+
+  ``IIO_BUFFER_DMABUF_ENQUEUE_IOCTL(struct iio_dmabuf *iio_dmabuf)``
+    Enqueue a previously attached DMABUF object to the buffer queue.
+    Enqueued DMABUFs will be read from (if output buffer) or written to
+    (if input buffer) as long as the buffer is enabled.
diff --git a/Documentation/iio/index.rst b/Documentation/iio/index.rst
index 4c13bfa2865c..9cb4c50cb20d 100644
--- a/Documentation/iio/index.rst
+++ b/Documentation/iio/index.rst
@@ -9,6 +9,7 @@ Industrial I/O
 
    iio_configfs
    iio_devbuf
+   iio_dmabuf_api
    iio_tools
 
 Industrial I/O Kernel Drivers
-- 
2.43.0

Re: [PATCH v10 6/6] Documentation: iio: Document high-speed DMABUF based API

[Randy Dunlap]

Hi,

On 6/5/24 4:08 AM, Paul Cercueil wrote:
> Document the new DMABUF based API.
> 
> Signed-off-by: Paul Cercueil <paul@crapouillou.net>
> Signed-off-by: Nuno Sa <nuno.sa@analog.com>
> 
> ---
> v2: - Explicitly state that the new interface is optional and is
>       not implemented by all drivers.
>     - The IOCTLs can now only be called on the buffer FD returned by
>       IIO_BUFFER_GET_FD_IOCTL.
>     - Move the page up a bit in the index since it is core stuff and not
>       driver-specific.
> 
> v3: Update the documentation to reflect the new API.
> 
> v5: Use description lists for the documentation of the three new IOCTLs
>     instead of abusing subsections.
> 
> v8: Renamed dmabuf_api.rst -> iio_dmabuf_api.rst, and updated index.rst
>     whose format changed in iio/togreg.
> ---
>  Documentation/iio/iio_dmabuf_api.rst | 54 ++++++++++++++++++++++++++++
>  Documentation/iio/index.rst          |  1 +
>  2 files changed, 55 insertions(+)
>  create mode 100644 Documentation/iio/iio_dmabuf_api.rst
> 
> diff --git a/Documentation/iio/iio_dmabuf_api.rst b/Documentation/iio/iio_dmabuf_api.rst
> new file mode 100644
> index 000000000000..1cd6cd51a582
> --- /dev/null
> +++ b/Documentation/iio/iio_dmabuf_api.rst
> @@ -0,0 +1,54 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +===================================
> +High-speed DMABUF interface for IIO
> +===================================
> +
> +1. Overview
> +===========
> +
> +The Industrial I/O subsystem supports access to buffers through a
> +file-based interface, with read() and write() access calls through the
> +IIO device's dev node.
> +
> +It additionally supports a DMABUF based interface, where the userspace
> +can attach DMABUF objects (externally created) to a IIO buffer, and

I would say/write:                                to an IIO buffer,

> +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.
> +
> +The userspace application can also memory-map the DMABUF objects, and
> +access the sample data directly. The advantage of doing this vs. the
> +read() interface is that it avoids an extra copy of the data between the
> +kernel and userspace. This is particularly useful for high-speed devices
> +which produce several megabytes or even gigabytes of data per second.
> +It does however increase the userspace-kernelspace synchronization
> +overhead, as the DMA_BUF_SYNC_START and DMA_BUF_SYNC_END IOCTLs have to
> +be used for data integrity.
> +
> +2. User API
> +===========
> +
> +As part of this interface, three new IOCTLs have been added. These three
> +IOCTLs have to be performed on the IIO buffer's file descriptor,
> +obtained using the IIO_BUFFER_GET_FD_IOCTL() ioctl.
> +
> +  ``IIO_BUFFER_DMABUF_ATTACH_IOCTL(int)``

                                     (int fd)
?

> +    Attach the DMABUF object, identified by its file descriptor, to the
> +    IIO buffer. Returns zero on success, and a negative errno value on
> +    error.
> +
> +  ``IIO_BUFFER_DMABUF_DETACH_IOCTL(int)``

ditto.

> +    Detach the given DMABUF object, identified by its file descriptor,
> +    from the IIO buffer. Returns zero on success, and a negative errno
> +    value on error.
> +
> +    Note that closing the IIO buffer's file descriptor will
> +    automatically detach all previously attached DMABUF objects.
> +
> +  ``IIO_BUFFER_DMABUF_ENQUEUE_IOCTL(struct iio_dmabuf *iio_dmabuf)``
> +    Enqueue a previously attached DMABUF object to the buffer queue.
> +    Enqueued DMABUFs will be read from (if output buffer) or written to
> +    (if input buffer) as long as the buffer is enabled.

thanks.
-- 
#Randy
https://people.kernel.org/tglx/notes-about-netiquette
https://subspace.kernel.org/etiquette.html

Re: [PATCH v10 6/6] Documentation: iio: Document high-speed DMABUF based API

[Paul Cercueil]

Hi Randy,

Le jeudi 06 juin 2024 à 10:32 -0700, Randy Dunlap a écrit :
> Hi,
> 
> On 6/5/24 4:08 AM, Paul Cercueil wrote:
> > Document the new DMABUF based API.
> > 
> > Signed-off-by: Paul Cercueil <paul@crapouillou.net>
> > Signed-off-by: Nuno Sa <nuno.sa@analog.com>
> > 
> > ---
> > v2: - Explicitly state that the new interface is optional and is
> >       not implemented by all drivers.
> >     - The IOCTLs can now only be called on the buffer FD returned
> > by
> >       IIO_BUFFER_GET_FD_IOCTL.
> >     - Move the page up a bit in the index since it is core stuff
> > and not
> >       driver-specific.
> > 
> > v3: Update the documentation to reflect the new API.
> > 
> > v5: Use description lists for the documentation of the three new
> > IOCTLs
> >     instead of abusing subsections.
> > 
> > v8: Renamed dmabuf_api.rst -> iio_dmabuf_api.rst, and updated
> > index.rst
> >     whose format changed in iio/togreg.
> > ---
> >  Documentation/iio/iio_dmabuf_api.rst | 54
> > ++++++++++++++++++++++++++++
> >  Documentation/iio/index.rst          |  1 +
> >  2 files changed, 55 insertions(+)
> >  create mode 100644 Documentation/iio/iio_dmabuf_api.rst
> > 
> > diff --git a/Documentation/iio/iio_dmabuf_api.rst
> > b/Documentation/iio/iio_dmabuf_api.rst
> > new file mode 100644
> > index 000000000000..1cd6cd51a582
> > --- /dev/null
> > +++ b/Documentation/iio/iio_dmabuf_api.rst
> > @@ -0,0 +1,54 @@
> > +.. SPDX-License-Identifier: GPL-2.0
> > +
> > +===================================
> > +High-speed DMABUF interface for IIO
> > +===================================
> > +
> > +1. Overview
> > +===========
> > +
> > +The Industrial I/O subsystem supports access to buffers through a
> > +file-based interface, with read() and write() access calls through
> > the
> > +IIO device's dev node.
> > +
> > +It additionally supports a DMABUF based interface, where the
> > userspace
> > +can attach DMABUF objects (externally created) to a IIO buffer,
> > and
> 
> I would say/write:                                to an IIO buffer,

Right.

> > +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.
> > +
> > +The userspace application can also memory-map the DMABUF objects,
> > and
> > +access the sample data directly. The advantage of doing this vs.
> > the
> > +read() interface is that it avoids an extra copy of the data
> > between the
> > +kernel and userspace. This is particularly useful for high-speed
> > devices
> > +which produce several megabytes or even gigabytes of data per
> > second.
> > +It does however increase the userspace-kernelspace synchronization
> > +overhead, as the DMA_BUF_SYNC_START and DMA_BUF_SYNC_END IOCTLs
> > have to
> > +be used for data integrity.
> > +
> > +2. User API
> > +===========
> > +
> > +As part of this interface, three new IOCTLs have been added. These
> > three
> > +IOCTLs have to be performed on the IIO buffer's file descriptor,
> > +obtained using the IIO_BUFFER_GET_FD_IOCTL() ioctl.
> > +
> > +  ``IIO_BUFFER_DMABUF_ATTACH_IOCTL(int)``
> 
>                                      (int fd)
> ?

Yes, I can change that. Although it's very obvious what the "int" is
for, given the text above.

> 
> > +    Attach the DMABUF object, identified by its file descriptor,
> > to the
> > +    IIO buffer. Returns zero on success, and a negative errno
> > value on
> > +    error.
> > +
> > +  ``IIO_BUFFER_DMABUF_DETACH_IOCTL(int)``
> 
> ditto.
> 
> > +    Detach the given DMABUF object, identified by its file
> > descriptor,
> > +    from the IIO buffer. Returns zero on success, and a negative
> > errno
> > +    value on error.
> > +
> > +    Note that closing the IIO buffer's file descriptor will
> > +    automatically detach all previously attached DMABUF objects.
> > +
> > +  ``IIO_BUFFER_DMABUF_ENQUEUE_IOCTL(struct iio_dmabuf
> > *iio_dmabuf)``
> > +    Enqueue a previously attached DMABUF object to the buffer
> > queue.
> > +    Enqueued DMABUFs will be read from (if output buffer) or
> > written to
> > +    (if input buffer) as long as the buffer is enabled.
> 
> thanks.

Cheers,
-Paul

Re: [PATCH v10 6/6] Documentation: iio: Document high-speed DMABUF based API

[Randy Dunlap]

Hi Paul.

On 6/7/24 12:44 AM, Paul Cercueil wrote:
> Hi Randy,
> 
> Le jeudi 06 juin 2024 à 10:32 -0700, Randy Dunlap a écrit :
>> Hi,
>>
>> On 6/5/24 4:08 AM, Paul Cercueil wrote:
>>> Document the new DMABUF based API.
>>>
>>> Signed-off-by: Paul Cercueil <paul@crapouillou.net>
>>> Signed-off-by: Nuno Sa <nuno.sa@analog.com>
>>>
>>> ---
>>> v2: - Explicitly state that the new interface is optional and is
>>>       not implemented by all drivers.
>>>     - The IOCTLs can now only be called on the buffer FD returned
>>> by
>>>       IIO_BUFFER_GET_FD_IOCTL.
>>>     - Move the page up a bit in the index since it is core stuff
>>> and not
>>>       driver-specific.
>>>
>>> v3: Update the documentation to reflect the new API.
>>>
>>> v5: Use description lists for the documentation of the three new
>>> IOCTLs
>>>     instead of abusing subsections.
>>>
>>> v8: Renamed dmabuf_api.rst -> iio_dmabuf_api.rst, and updated
>>> index.rst
>>>     whose format changed in iio/togreg.
>>> ---
>>>  Documentation/iio/iio_dmabuf_api.rst | 54
>>> ++++++++++++++++++++++++++++
>>>  Documentation/iio/index.rst          |  1 +
>>>  2 files changed, 55 insertions(+)
>>>  create mode 100644 Documentation/iio/iio_dmabuf_api.rst
>>>
>>> diff --git a/Documentation/iio/iio_dmabuf_api.rst
>>> b/Documentation/iio/iio_dmabuf_api.rst
>>> new file mode 100644
>>> index 000000000000..1cd6cd51a582
>>> --- /dev/null
>>> +++ b/Documentation/iio/iio_dmabuf_api.rst
>>> @@ -0,0 +1,54 @@
>>> +.. SPDX-License-Identifier: GPL-2.0
>>> +
>>> +===================================
>>> +High-speed DMABUF interface for IIO
>>> +===================================
>>> +
>>> +1. Overview
>>> +===========
>>> +
>>> +The Industrial I/O subsystem supports access to buffers through a
>>> +file-based interface, with read() and write() access calls through
>>> the
>>> +IIO device's dev node.
>>> +
>>> +It additionally supports a DMABUF based interface, where the
>>> userspace
>>> +can attach DMABUF objects (externally created) to a IIO buffer,
>>> and
>>
>> I would say/write:                                to an IIO buffer,
> 
> Right.
> 
>>> +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.
>>> +
>>> +The userspace application can also memory-map the DMABUF objects,
>>> and
>>> +access the sample data directly. The advantage of doing this vs.
>>> the
>>> +read() interface is that it avoids an extra copy of the data
>>> between the
>>> +kernel and userspace. This is particularly useful for high-speed
>>> devices
>>> +which produce several megabytes or even gigabytes of data per
>>> second.
>>> +It does however increase the userspace-kernelspace synchronization
>>> +overhead, as the DMA_BUF_SYNC_START and DMA_BUF_SYNC_END IOCTLs
>>> have to
>>> +be used for data integrity.
>>> +
>>> +2. User API
>>> +===========
>>> +
>>> +As part of this interface, three new IOCTLs have been added. These
>>> three
>>> +IOCTLs have to be performed on the IIO buffer's file descriptor,
>>> +obtained using the IIO_BUFFER_GET_FD_IOCTL() ioctl.
>>> +
>>> +  ``IIO_BUFFER_DMABUF_ATTACH_IOCTL(int)``
>>
>>                                      (int fd)
>> ?
> 
> Yes, I can change that. Although it's very obvious what the "int" is
> for, given the text above.
> 

Yes. This is just to be consistent with the text below:

+  ``IIO_BUFFER_DMABUF_ENQUEUE_IOCTL(struct iio_dmabuf *iio_dmabuf)``

>>
>>> +    Attach the DMABUF object, identified by its file descriptor,
>>> to the
>>> +    IIO buffer. Returns zero on success, and a negative errno
>>> value on
>>> +    error.
>>> +
>>> +  ``IIO_BUFFER_DMABUF_DETACH_IOCTL(int)``
>>
>> ditto.
>>
>>> +    Detach the given DMABUF object, identified by its file
>>> descriptor,
>>> +    from the IIO buffer. Returns zero on success, and a negative
>>> errno
>>> +    value on error.
>>> +
>>> +    Note that closing the IIO buffer's file descriptor will
>>> +    automatically detach all previously attached DMABUF objects.
>>> +
>>> +  ``IIO_BUFFER_DMABUF_ENQUEUE_IOCTL(struct iio_dmabuf
>>> *iio_dmabuf)``
>>> +    Enqueue a previously attached DMABUF object to the buffer
>>> queue.
>>> +    Enqueued DMABUFs will be read from (if output buffer) or
>>> written to
>>> +    (if input buffer) as long as the buffer is enabled.
>>
>> thanks.
> 
> Cheers,
> -Paul

thanks.
-- 
#Randy
https://people.kernel.org/tglx/notes-about-netiquette
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Re: [PATCH v10 0/6] iio: new DMABUF based API v10

[Jonathan Cameron]

On Wed,  5 Jun 2024 13:08:39 +0200
Paul Cercueil <paul@crapouillou.net> wrote:

> Hi Jonathan,
> 
> Here is a revised (and hopefully final?) version of my DMABUF patchset.

Fingers crossed it's just docs changes for v11.

So on to the details of how to merge this...
For the DMAEngine maintainers:
Given IIO changes dominate this series it makes sense for me to pick it up
through IIO.

Do you want an immutable branch with the first patch on it, or is this
unlikely to cause merge conflicts with any other ongoing work in dmabuffer
land?

I'm fine either way and if I don't hear back on this will do an immutable
branch and announce it when I apply v11 (I hope!)

Jonathan

> 
> This v10 removes the extra "flags" parameter of
> dmaengine_prep_peripheral_dma_vec(), and adds kernel doc to the function
> as Vinod requested.
> 
> As Nuno upstreamed support for output buffers, I (slightly) modified
> patch 5/6 and now output buffers are supported with the DMABUF API.
> All I did was remove a "fail if output" check really.
> 
> This was based on next-20240605.
> 
> Changelog:
> - [1/6]:
>   - Add kernel doc to dmaengine_prep_peripheral_dma_vec()
>   - Remove extra flags parameter
> - [2/6]:
>   - Use the new function prototype (without the extra prep_flags).
> - [5/6]:
>   - Remove extra flags parameter to dmaengine_prep_peripheral_dma_vec()
>   - Add support for TX transfers
> 
> Cheers,
> -Paul
> 
> Paul Cercueil (6):
>   dmaengine: Add API function dmaengine_prep_peripheral_dma_vec()
>   dmaengine: dma-axi-dmac: Implement device_prep_peripheral_dma_vec
>   iio: core: Add new DMABUF interface infrastructure
>   iio: buffer-dma: Enable support for DMABUFs
>   iio: buffer-dmaengine: Support new DMABUF based userspace API
>   Documentation: iio: Document high-speed DMABUF based API
> 
>  Documentation/iio/iio_dmabuf_api.rst          |  54 ++
>  Documentation/iio/index.rst                   |   1 +
>  drivers/dma/dma-axi-dmac.c                    |  40 ++
>  drivers/iio/Kconfig                           |   1 +
>  drivers/iio/buffer/industrialio-buffer-dma.c  | 180 ++++++-
>  .../buffer/industrialio-buffer-dmaengine.c    |  62 ++-
>  drivers/iio/industrialio-buffer.c             | 462 ++++++++++++++++++
>  include/linux/dmaengine.h                     |  33 ++
>  include/linux/iio/buffer-dma.h                |  31 ++
>  include/linux/iio/buffer_impl.h               |  30 ++
>  include/uapi/linux/iio/buffer.h               |  22 +
>  11 files changed, 896 insertions(+), 20 deletions(-)
>  create mode 100644 Documentation/iio/iio_dmabuf_api.rst
>