Re: [RFC PATCH 04/12] staging: android: ion: Call dma_map_sg for syncing and mapping

[Laurent Pinchart]

Hi Laura,

Thank you for the patch.

On Thursday 02 Mar 2017 13:44:36 Laura Abbott wrote:
> Technically, calling dma_buf_map_attachment should return a buffer
> properly dma_mapped. Add calls to dma_map_sg to begin_cpu_access to
> ensure this happens. As a side effect, this lets Ion buffers take
> advantage of the dma_buf sync ioctls.
> 
> Signed-off-by: Laura Abbott <labbott@xxxxxxxxxx>
> ---
>  drivers/staging/android/ion/ion.c | 101 +++++++++++++++++------------------
>  1 file changed, 50 insertions(+), 51 deletions(-)
> 
> diff --git a/drivers/staging/android/ion/ion.c
> b/drivers/staging/android/ion/ion.c index ce4adac..a931b30 100644
> --- a/drivers/staging/android/ion/ion.c
> +++ b/drivers/staging/android/ion/ion.c
> @@ -795,10 +795,6 @@ void ion_client_destroy(struct ion_client *client)
>  }
>  EXPORT_SYMBOL(ion_client_destroy);
> 
> -static void ion_buffer_sync_for_device(struct ion_buffer *buffer,
> -				       struct device *dev,
> -				       enum dma_data_direction direction);
> -
>  static struct sg_table *dup_sg_table(struct sg_table *table)
>  {
>  	struct sg_table *new_table;
> @@ -825,22 +821,43 @@ static struct sg_table *dup_sg_table(struct sg_table
> *table) return new_table;
>  }
> 
> +static void free_duped_table(struct sg_table *table)
> +{
> +	sg_free_table(table);
> +	kfree(table);
> +}
> +
>  static struct sg_table *ion_map_dma_buf(struct dma_buf_attachment
> *attachment, enum dma_data_direction direction)
>  {
>  	struct dma_buf *dmabuf = attachment->dmabuf;
>  	struct ion_buffer *buffer = dmabuf->priv;
> +	struct sg_table *table;
> +	int ret;
> +
> +	/*
> +	 * TODO: Need to sync wrt CPU or device completely owning?
> +	 */
> +
> +	table = dup_sg_table(buffer->sg_table);
> 
> -	ion_buffer_sync_for_device(buffer, attachment->dev, direction);
> -	return dup_sg_table(buffer->sg_table);
> +	if (!dma_map_sg(attachment->dev, table->sgl, table->nents,
> +			direction)){
> +		ret = -ENOMEM;
> +		goto err;
> +	}
> +
> +err:
> +	free_duped_table(table);
> +	return ERR_PTR(ret);
>  }
> 
>  static void ion_unmap_dma_buf(struct dma_buf_attachment *attachment,
>  			      struct sg_table *table,
>  			      enum dma_data_direction direction)
>  {
> -	sg_free_table(table);
> -	kfree(table);
> +	dma_unmap_sg(attachment->dev, table->sgl, table->nents, direction);
> +	free_duped_table(table);
>  }
> 
>  void ion_pages_sync_for_device(struct device *dev, struct page *page,
> @@ -864,38 +881,6 @@ struct ion_vma_list {
>  	struct vm_area_struct *vma;
>  };
> 
> -static void ion_buffer_sync_for_device(struct ion_buffer *buffer,
> -				       struct device *dev,
> -				       enum dma_data_direction dir)
> -{
> -	struct ion_vma_list *vma_list;
> -	int pages = PAGE_ALIGN(buffer->size) / PAGE_SIZE;
> -	int i;
> -
> -	pr_debug("%s: syncing for device %s\n", __func__,
> -		 dev ? dev_name(dev) : "null");
> -
> -	if (!ion_buffer_fault_user_mappings(buffer))
> -		return;
> -
> -	mutex_lock(&buffer->lock);
> -	for (i = 0; i < pages; i++) {
> -		struct page *page = buffer->pages[i];
> -
> -		if (ion_buffer_page_is_dirty(page))
> -			ion_pages_sync_for_device(dev, ion_buffer_page(page),
> -						  PAGE_SIZE, dir);
> -
> -		ion_buffer_page_clean(buffer->pages + i);
> -	}
> -	list_for_each_entry(vma_list, &buffer->vmas, list) {
> -		struct vm_area_struct *vma = vma_list->vma;
> -
> -		zap_page_range(vma, vma->vm_start, vma->vm_end - vma-
>vm_start);
> -	}
> -	mutex_unlock(&buffer->lock);
> -}
> -
>  static int ion_vm_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
>  {
>  	struct ion_buffer *buffer = vma->vm_private_data;
> @@ -1014,16 +999,24 @@ static int ion_dma_buf_begin_cpu_access(struct
> dma_buf *dmabuf, struct ion_buffer *buffer = dmabuf->priv;
>  	void *vaddr;
> 
> -	if (!buffer->heap->ops->map_kernel) {
> -		pr_err("%s: map kernel is not implemented by this heap.\n",
> -		       __func__);
> -		return -ENODEV;
> +	/*
> +	 * TODO: Move this elsewhere because we don't always need a vaddr
> +	 */
> +	if (buffer->heap->ops->map_kernel) {
> +		mutex_lock(&buffer->lock);
> +		vaddr = ion_buffer_kmap_get(buffer);
> +		mutex_unlock(&buffer->lock);
>  	}
> 
> -	mutex_lock(&buffer->lock);
> -	vaddr = ion_buffer_kmap_get(buffer);
> -	mutex_unlock(&buffer->lock);
> -	return PTR_ERR_OR_ZERO(vaddr);
> +	/*
> +	 * Close enough right now? Flag to skip sync?
> +	 */
> +	if (!dma_map_sg(buffer->dev->dev.this_device, buffer->sg_table->sgl,
> +			buffer->sg_table->nents,
> +                        DMA_BIDIRECTIONAL))

Aren't the dma_(un)map_* calls supposed to take a real, physical device as 
their first argument ? Beside, this doesn't seem to be the right place to 
create the mapping, as you mentioned in the commit message the buffer should 
be mapped in the dma_buf map handler. This is something that needs to be 
fixed, especially in the light of the comment in ion_buffer_create():

        /*
         * this will set up dma addresses for the sglist -- it is not
         * technically correct as per the dma api -- a specific
         * device isn't really taking ownership here.  However, in practice on
         * our systems the only dma_address space is physical addresses.
         * Additionally, we can't afford the overhead of invalidating every
         * allocation via dma_map_sg. The implicit contract here is that
         * memory coming from the heaps is ready for dma, ie if it has a
         * cached mapping that mapping has been invalidated
         */

That's a showstopper in my opinion, the DMA address space can't be restricted 
to physical addresses, IOMMU have to be supported.

> +		return -ENOMEM;
> +
> +	return 0;
>  }
> 
>  static int ion_dma_buf_end_cpu_access(struct dma_buf *dmabuf,
> @@ -1031,9 +1024,15 @@ static int ion_dma_buf_end_cpu_access(struct dma_buf
> *dmabuf, {
>  	struct ion_buffer *buffer = dmabuf->priv;
> 
> -	mutex_lock(&buffer->lock);
> -	ion_buffer_kmap_put(buffer);
> -	mutex_unlock(&buffer->lock);
> +	if (buffer->heap->ops->map_kernel) {
> +		mutex_lock(&buffer->lock);
> +		ion_buffer_kmap_put(buffer);
> +		mutex_unlock(&buffer->lock);
> +	}
> +
> +	dma_unmap_sg(buffer->dev->dev.this_device, buffer->sg_table->sgl,
> +			buffer->sg_table->nents,
> +			DMA_BIDIRECTIONAL);
> 
>  	return 0;
>  }

-- 
Regards,

Laurent Pinchart