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

On Mon, 7 Feb 2022 12:59:28 +0000 Paul Cercueil paul@crapouillou.net 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@crapouillou.net

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?

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;

};

/**