drm/i915: Return a mask of the active rings in the high word of busy_ioctl

The intention is to help select which engine to use for copies with
interoperating clients - such as a GL client making a request to the X
server to perform a SwapBuffers, which may require copying from the
active GL back buffer to the X front buffer.

We choose to report a mask of the active rings to future proof the
interface against any changes which may allow for the object to reside
upon multiple rings.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
[danvet: bikeshed away the write ring mask and add the explanation
Chris sent in a follow-up mail why we decided to use masks.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 5 insertions, 1 deletions

diff --git a/include/drm/i915_drm.h b/include/drm/i915_drm.h
index b923b032743f..0f149fe32211 100644
--- a/include/drm/i915_drm.h
+++ b/include/drm/i915_drm.h
@@ -704,7 +704,11 @@ struct drm_i915_gem_busy {
         /** Handle of the buffer to check for busy */
         __u32 handle;
 
-        /** Return busy status (1 if busy, 0 if idle) */
+        /** Return busy status (1 if busy, 0 if idle).
+         * The high word is used to indicate on which rings the object
+         * currently resides:
+         *  16:31 - busy (r or r/w) rings (16 render, 17 bsd, 18 blt, etc)
+         */
         __u32 busy;
 };