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

Laurent Pinchart
2017-03-03T16:37:47Z

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@redhat.com>
> ---
> 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