Hi Ben and Sumit,
Please refer to comments below:
On 02/22/2012 08:29 PM, Ben Widawsky wrote:
dma-buf export implementation. Heavily influenced by Dave Airlie's proof
of concept work.
Cc: Daniel Vetter<daniel.vetter@xxxxxxxx>
Cc: Dave Airlie<airlied@xxxxxxxxxx>
Signed-off-by: Ben Widawsky<ben@xxxxxxxxxxxx>
---
drivers/gpu/drm/vgem/Makefile | 2 +-
drivers/gpu/drm/vgem/vgem_dma_buf.c | 128 +++++++++++++++++++++++++++++++++++
drivers/gpu/drm/vgem/vgem_drv.c | 6 ++
drivers/gpu/drm/vgem/vgem_drv.h | 7 ++
4 files changed, 142 insertions(+), 1 deletions(-)
create mode 100644 drivers/gpu/drm/vgem/vgem_dma_buf.c
[snip]
+struct sg_table *vgem_gem_map_dma_buf(struct dma_buf_attachment *attachment,
+ enum dma_data_direction dir)
+{
+ struct drm_vgem_gem_object *obj = attachment->dmabuf->priv;
+ struct sg_table *sg;
+ int ret;
+
+ ret = vgem_gem_get_pages(obj);
+ if (ret) {
+ vgem_gem_put_pages(obj);
is it safe to call vgem_gem_put_pages if vgem_gem_get_pages failed (I
mean ret < 0 was returned) ?
+ return NULL;
+ }
+
+ BUG_ON(obj->pages == NULL);
+
+ sg = drm_prime_pages_to_sg(obj->pages, obj->base.size / PAGE_SIZE);
if drm_prime_pages_to_sg fails then you should call vgem_gem_put_pages
for cleanup.
+ return sg;
+}
The documentation of DMABUF says fallowing words about map_dma_buf callback.
"It is one of the buffer operations that must be implemented by the
exporter. It should return the sg_table containing scatterlist for this
buffer, mapped into caller's address space."
The scatterlist returned by drm_prime_pages_to_sg is not mapped to any
device. The map_dma_buf callback should call dma_map_sg for caller
device, which is attachment->dev. Otherwise the implementation is not
consistent with the DMABUF spec.
I think that it should be chosen to change implementation in map_dma_buf
in DRM drivers or to drop mentioned sentence from the DMABUF spec.
I bear to the second solution because IMO there is no reliable way of
mapping a scatterlist to importer device by an exporter. The dma_map_sg
could be used but not all drivers makes use of DMA framework.
Sumit, what is your opinion about it?
+
+void vgem_gem_unmap_dma_buf(struct dma_buf_attachment *attachment,
+ struct sg_table *sg)
+{
+ sg_free_table(sg);
+ kfree(sg);
+}
+
+void vgem_gem_release(struct dma_buf *buf)
+{
+ struct drm_vgem_gem_object *obj = buf->priv;
+
+ BUG_ON(buf != obj->base.export_dma_buf);
+
+ obj->base.prime_fd = -1;
+ obj->base.export_dma_buf = NULL;
+ drm_gem_object_unreference_unlocked(&obj->base);
+}
+
+struct dma_buf_ops vgem_dmabuf_ops = {
+ .map_dma_buf = vgem_gem_map_dma_buf,
+ .unmap_dma_buf = vgem_gem_unmap_dma_buf,
+ .release = vgem_gem_release
+};
+
Regards,
Tomasz Stanislawski
_______________________________________________
dri-devel mailing list
dri-devel@xxxxxxxxxxxxxxxxxxxxx
http://lists.freedesktop.org/mailman/listinfo/dri-devel
