Rendering operations to the dma-buf are tracked implicitly via the reservation_object (dmabuf->resv). This is used to allow poll() to wait upon outstanding rendering (or just query the current status of rendering). The dma-buf sync ioctl allows userspace to prepare the dma-buf for CPU access, which should include waiting upon rendering. (Some drivers may need to do more work to ensure that the dma-buf mmap is coherent as well as complete.)
Signed-off-by: Chris Wilson chris@chris-wilson.co.uk Cc: Sumit Semwal sumit.semwal@linaro.org Cc: Daniel Vetter daniel.vetter@ffwll.ch Cc: linux-media@vger.kernel.org Cc: dri-devel@lists.freedesktop.org Cc: linaro-mm-sig@lists.linaro.org Cc: linux-kernel@vger.kernel.org ---
I'm wondering whether it makes sense just to always do the wait first. It is one of the first operations every driver has to make. A driver that wants to implement it differently (e.g. they can special case native waits) will still require a wait on the reservation object to finish external rendering. -Chris
--- drivers/dma-buf/dma-buf.c | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+)
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c index ddaee60ae52a..123f14b8e882 100644 --- a/drivers/dma-buf/dma-buf.c +++ b/drivers/dma-buf/dma-buf.c @@ -586,6 +586,22 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach, } EXPORT_SYMBOL_GPL(dma_buf_unmap_attachment);
+static int __dma_buf_begin_cpu_access(struct dma_buf *dmabuf, + enum dma_data_direction direction) +{ + bool write = (direction == DMA_BIDIRECTIONAL || + direction == DMA_TO_DEVICE); + struct reservation_object *resv = dma_buf->resv; + long ret; + + /* Wait on any implicit rendering fences */ + ret = reservation_object_wait_timeout_rcu(resv, write, true, + MAX_SCHEDULE_TIMEOUT); + if (ret < 0) + return ret; + + return 0; +}
/** * dma_buf_begin_cpu_access - Must be called before accessing a dma_buf from the @@ -607,6 +623,8 @@ int dma_buf_begin_cpu_access(struct dma_buf *dmabuf,
if (dmabuf->ops->begin_cpu_access) ret = dmabuf->ops->begin_cpu_access(dmabuf, direction); + else + ret = __dma_buf_begin_cpu_access(dmabuf, direction);
return ret; }