On Tue, Jun 21, 2016 at 08:04:00AM +0100, Chris Wilson wrote:
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.
Worst case (if the driver uses reservation objects also internally) we'll end up calling this twice. It should be cheap enough to do that. I'll add a few folks who might want to chip in with an opinion ... -Daniel
-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;
}
2.8.1