Re: [PATCH v2 07/12] iio: buffer-dma: Use DMABUFs instead of custom solution

Christian König <christian.koenig@xxxxxxx> · Mon, 28 Mar 2022 19:54:57 +0200

Am 28.03.22 um 19:54 schrieb Jonathan Cameron:
On Mon,  7 Feb 2022 12:59:28 +0000
Paul Cercueil <paul@xxxxxxxxxxxxxxx> wrote:

Enhance the current fileio code by using DMABUF objects instead of
custom buffers.

This adds more code than it removes, but:
- a lot of the complexity can be dropped, e.g. custom kref and
   iio_buffer_block_put_atomic() are not needed anymore;
- it will be much easier to introduce an API to export these DMABUF
   objects to userspace in a following patch.

Signed-off-by: Paul Cercueil <paul@xxxxxxxxxxxxxxx>
Hi Paul,

I'm a bit rusty on dma mappings, but you seem to have
a mixture of streaming and coherent mappings going on in here.

Is it the case that the current code is using the coherent mappings
and a potential 'other user' of the dma buffer might need
streaming mappings?

Streaming mappings are generally not supported by DMA-buf.

You always have only coherent mappings.

Regards,
Christian.


Jonathan

---
  drivers/iio/buffer/industrialio-buffer-dma.c | 192 ++++++++++++-------
  include/linux/iio/buffer-dma.h               |   8 +-
  2 files changed, 122 insertions(+), 78 deletions(-)

diff --git a/drivers/iio/buffer/industrialio-buffer-dma.c b/drivers/iio/buffer/industrialio-buffer-dma.c
index 15ea7bc3ac08..54e6000cd2ee 100644
--- a/drivers/iio/buffer/industrialio-buffer-dma.c
+++ b/drivers/iio/buffer/industrialio-buffer-dma.c
@@ -14,6 +14,7 @@
  #include <linux/poll.h>
  #include <linux/iio/buffer_impl.h>
  #include <linux/iio/buffer-dma.h>
+#include <linux/dma-buf.h>
  #include <linux/dma-mapping.h>
  #include <linux/sizes.h>
  
@@ -90,103 +91,145 @@
   * callback is called from within the custom callback.
   */
  
-static void iio_buffer_block_release(struct kref *kref)
-{
-	struct iio_dma_buffer_block *block = container_of(kref,
-		struct iio_dma_buffer_block, kref);
-
-	WARN_ON(block->state != IIO_BLOCK_STATE_DEAD);
-
-	dma_free_coherent(block->queue->dev, PAGE_ALIGN(block->size),
-					block->vaddr, block->phys_addr);
-
-	iio_buffer_put(&block->queue->buffer);
-	kfree(block);
-}
-
-static void iio_buffer_block_get(struct iio_dma_buffer_block *block)
-{
-	kref_get(&block->kref);
-}
-
-static void iio_buffer_block_put(struct iio_dma_buffer_block *block)
-{
-	kref_put(&block->kref, iio_buffer_block_release);
-}
-
-/*
- * dma_free_coherent can sleep, hence we need to take some special care to be
- * able to drop a reference from an atomic context.
- */
-static LIST_HEAD(iio_dma_buffer_dead_blocks);
-static DEFINE_SPINLOCK(iio_dma_buffer_dead_blocks_lock);
-
-static void iio_dma_buffer_cleanup_worker(struct work_struct *work)
-{
-	struct iio_dma_buffer_block *block, *_block;
-	LIST_HEAD(block_list);
-
-	spin_lock_irq(&iio_dma_buffer_dead_blocks_lock);
-	list_splice_tail_init(&iio_dma_buffer_dead_blocks, &block_list);
-	spin_unlock_irq(&iio_dma_buffer_dead_blocks_lock);
-
-	list_for_each_entry_safe(block, _block, &block_list, head)
-		iio_buffer_block_release(&block->kref);
-}
-static DECLARE_WORK(iio_dma_buffer_cleanup_work, iio_dma_buffer_cleanup_worker);
-
-static void iio_buffer_block_release_atomic(struct kref *kref)
-{
+struct iio_buffer_dma_buf_attachment {
+	struct scatterlist sgl;
+	struct sg_table sg_table;
  	struct iio_dma_buffer_block *block;
-	unsigned long flags;
-
-	block = container_of(kref, struct iio_dma_buffer_block, kref);
-
-	spin_lock_irqsave(&iio_dma_buffer_dead_blocks_lock, flags);
-	list_add_tail(&block->head, &iio_dma_buffer_dead_blocks);
-	spin_unlock_irqrestore(&iio_dma_buffer_dead_blocks_lock, flags);
-
-	schedule_work(&iio_dma_buffer_cleanup_work);
-}
-
-/*
- * Version of iio_buffer_block_put() that can be called from atomic context
- */
-static void iio_buffer_block_put_atomic(struct iio_dma_buffer_block *block)
-{
-	kref_put(&block->kref, iio_buffer_block_release_atomic);
-}
+};
  
  static struct iio_dma_buffer_queue *iio_buffer_to_queue(struct iio_buffer *buf)
  {
  	return container_of(buf, struct iio_dma_buffer_queue, buffer);
  }
  
+static struct iio_buffer_dma_buf_attachment *
+to_iio_buffer_dma_buf_attachment(struct sg_table *table)
+{
+	return container_of(table, struct iio_buffer_dma_buf_attachment, sg_table);
+}
+
+static void iio_buffer_block_get(struct iio_dma_buffer_block *block)
+{
+	get_dma_buf(block->dmabuf);
+}
+
+static void iio_buffer_block_put(struct iio_dma_buffer_block *block)
+{
+	dma_buf_put(block->dmabuf);
+}
+
+static int iio_buffer_dma_buf_attach(struct dma_buf *dbuf,
+				     struct dma_buf_attachment *at)
+{
+	at->priv = dbuf->priv;
+
+	return 0;
+}
+
+static struct sg_table *iio_buffer_dma_buf_map(struct dma_buf_attachment *at,
+					       enum dma_data_direction dma_dir)
+{
+	struct iio_dma_buffer_block *block = at->priv;
+	struct iio_buffer_dma_buf_attachment *dba;
+	int ret;
+
+	dba = kzalloc(sizeof(*dba), GFP_KERNEL);
+	if (!dba)
+		return ERR_PTR(-ENOMEM);
+
+	sg_init_one(&dba->sgl, block->vaddr, PAGE_ALIGN(block->size));
+	dba->sg_table.sgl = &dba->sgl;
+	dba->sg_table.nents = 1;
+	dba->block = block;
+
+	ret = dma_map_sgtable(at->dev, &dba->sg_table, dma_dir, 0);
+	if (ret) {
+		kfree(dba);
+		return ERR_PTR(ret);
+	}
+
+	return &dba->sg_table;
+}
+
+static void iio_buffer_dma_buf_unmap(struct dma_buf_attachment *at,
+				     struct sg_table *sg_table,
+				     enum dma_data_direction dma_dir)
+{
+	struct iio_buffer_dma_buf_attachment *dba =
+		to_iio_buffer_dma_buf_attachment(sg_table);
+
+	dma_unmap_sgtable(at->dev, &dba->sg_table, dma_dir, 0);
+	kfree(dba);
+}
+
+static void iio_buffer_dma_buf_release(struct dma_buf *dbuf)
+{
+	struct iio_dma_buffer_block *block = dbuf->priv;
+	struct iio_dma_buffer_queue *queue = block->queue;
+
+	WARN_ON(block->state != IIO_BLOCK_STATE_DEAD);
+
+	mutex_lock(&queue->lock);
+
+	dma_free_coherent(queue->dev, PAGE_ALIGN(block->size),
+			  block->vaddr, block->phys_addr);
+	kfree(block);
+
+	mutex_unlock(&queue->lock);
+	iio_buffer_put(&queue->buffer);
+}
+
+static const struct dma_buf_ops iio_dma_buffer_dmabuf_ops = {
+	.attach			= iio_buffer_dma_buf_attach,
+	.map_dma_buf		= iio_buffer_dma_buf_map,
+	.unmap_dma_buf		= iio_buffer_dma_buf_unmap,
+	.release		= iio_buffer_dma_buf_release,
+};
+
  static struct iio_dma_buffer_block *iio_dma_buffer_alloc_block(
  	struct iio_dma_buffer_queue *queue, size_t size)
  {
  	struct iio_dma_buffer_block *block;
+	DEFINE_DMA_BUF_EXPORT_INFO(einfo);
+	struct dma_buf *dmabuf;
+	int err = -ENOMEM;
  
  	block = kzalloc(sizeof(*block), GFP_KERNEL);
  	if (!block)
-		return NULL;
+		return ERR_PTR(err);
  
  	block->vaddr = dma_alloc_coherent(queue->dev, PAGE_ALIGN(size),
  		&block->phys_addr, GFP_KERNEL);
-	if (!block->vaddr) {
-		kfree(block);
-		return NULL;
+	if (!block->vaddr)
+		goto err_free_block;
+
+	einfo.ops = &iio_dma_buffer_dmabuf_ops;
+	einfo.size = PAGE_ALIGN(size);
+	einfo.priv = block;
+	einfo.flags = O_RDWR;
+
+	dmabuf = dma_buf_export(&einfo);
+	if (IS_ERR(dmabuf)) {
+		err = PTR_ERR(dmabuf);
+		goto err_free_dma;
  	}
  
+	block->dmabuf = dmabuf;
  	block->size = size;
  	block->state = IIO_BLOCK_STATE_DONE;
  	block->queue = queue;
  	INIT_LIST_HEAD(&block->head);
-	kref_init(&block->kref);
  
  	iio_buffer_get(&queue->buffer);
  
  	return block;
+
+err_free_dma:
+	dma_free_coherent(queue->dev, PAGE_ALIGN(size),
+			  block->vaddr, block->phys_addr);
+err_free_block:
+	kfree(block);
+	return ERR_PTR(err);
  }
  
  static void _iio_dma_buffer_block_done(struct iio_dma_buffer_block *block)
@@ -223,7 +266,7 @@ void iio_dma_buffer_block_done(struct iio_dma_buffer_block *block)
  	_iio_dma_buffer_block_done(block);
  	spin_unlock_irqrestore(&queue->list_lock, flags);
  
-	iio_buffer_block_put_atomic(block);
+	iio_buffer_block_put(block);
  	iio_dma_buffer_queue_wake(queue);
  }
  EXPORT_SYMBOL_GPL(iio_dma_buffer_block_done);
@@ -249,7 +292,8 @@ void iio_dma_buffer_block_list_abort(struct iio_dma_buffer_queue *queue,
  		list_del(&block->head);
  		block->bytes_used = 0;
  		_iio_dma_buffer_block_done(block);
-		iio_buffer_block_put_atomic(block);
+
+		iio_buffer_block_put(block);
  	}
  	spin_unlock_irqrestore(&queue->list_lock, flags);
  
@@ -340,8 +384,8 @@ int iio_dma_buffer_request_update(struct iio_buffer *buffer)
  
  		if (!block) {
  			block = iio_dma_buffer_alloc_block(queue, size);
-			if (!block) {
-				ret = -ENOMEM;
+			if (IS_ERR(block)) {
+				ret = PTR_ERR(block);
  				goto out_unlock;
  			}
  			queue->fileio.blocks[i] = block;
diff --git a/include/linux/iio/buffer-dma.h b/include/linux/iio/buffer-dma.h
index 490b93f76fa8..6b3fa7d2124b 100644
--- a/include/linux/iio/buffer-dma.h
+++ b/include/linux/iio/buffer-dma.h
@@ -8,7 +8,6 @@
  #define __INDUSTRIALIO_DMA_BUFFER_H__
  
  #include <linux/list.h>
-#include <linux/kref.h>
  #include <linux/spinlock.h>
  #include <linux/mutex.h>
  #include <linux/iio/buffer_impl.h>
@@ -16,6 +15,7 @@
  struct iio_dma_buffer_queue;
  struct iio_dma_buffer_ops;
  struct device;
+struct dma_buf;
  
  /**
   * enum iio_block_state - State of a struct iio_dma_buffer_block
@@ -39,8 +39,8 @@ enum iio_block_state {
   * @vaddr: Virutal address of the blocks memory
   * @phys_addr: Physical address of the blocks memory
   * @queue: Parent DMA buffer queue
- * @kref: kref used to manage the lifetime of block
   * @state: Current state of the block
+ * @dmabuf: Underlying DMABUF object
   */
  struct iio_dma_buffer_block {
  	/* May only be accessed by the owner of the block */
@@ -56,13 +56,13 @@ struct iio_dma_buffer_block {
  	size_t size;
  	struct iio_dma_buffer_queue *queue;
  
-	/* Must not be accessed outside the core. */
-	struct kref kref;
  	/*
  	 * Must not be accessed outside the core. Access needs to hold
  	 * queue->list_lock if the block is not owned by the core.
  	 */
  	enum iio_block_state state;
+
+	struct dma_buf *dmabuf;
  };
  
  /**







