[PATCH 04/20] drm/prime: add a bit of documentation about gem_obj->import_attach

[Daniel Vetter]

Lifetime rules seem to be solid around ->import_attach. So this patch
just properly documents them.

Note that pointing directly at the attachment might have issues for
devices that have multiple struct device *dev parts constituting the
logical gpu and so might need multiple attachment points. Similarly
for drm devices which don't need a dma attachment at all (like udl).

But fixing that up is material for different patches.

Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
---
 include/drm/drmP.h | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/include/drm/drmP.h b/include/drm/drmP.h
index cd57646..baf030c 100644
--- a/include/drm/drmP.h
+++ b/include/drm/drmP.h
@@ -681,7 +681,16 @@ struct drm_gem_object {
 	/* dma buf exported from this GEM object */
 	struct dma_buf *export_dma_buf;
 
-	/* dma buf attachment backing this object */
+	/**
+	 * import_attach - dma buf attachment backing this object
+	 *
+	 * Any foreign dma_buf imported as a gem object has this set to the
+	 * attachment point for the device. This is invariant over the lifetime
+	 * of a gem object.
+	 *
+	 * The driver's ->gem_free_object callback is responsible for cleaning
+	 * up the dma_buf attachment and references acquired at import time.
+	 */
 	struct dma_buf_attachment *import_attach;
 };
 
-- 
1.8.3.2