drm/i915: Pad GTT views of exec objects up to user specified size

Our GPUs impose certain requirements upon buffers that depend upon how
exactly they are used. Typically this is expressed as that they require
a larger surface than would be naively computed by pitch * height.
Normally such requirements are hidden away in the userspace driver, but
when we accept pointers from strangers and later impose extra conditions
on them, the original client allocator has no idea about the
monstrosities in the GPU and we require the userspace driver to inform
the kernel how many padding pages are required beyond the client
allocation.

v2: Long time, no see
v3: Try an anonymous union for uapi struct compatibility

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1470324762-2545-7-git-send-email-chris@chris-wilson.co.uk

1 files changed, 6 insertions, 2 deletions

diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
index 33ce5ff9556a..0f292733cffc 100644
--- a/include/uapi/drm/i915_drm.h
+++ b/include/uapi/drm/i915_drm.h
@@ -727,11 +727,15 @@ struct drm_i915_gem_exec_object2 {
 #define EXEC_OBJECT_WRITE		 (1<<2)
 #define EXEC_OBJECT_SUPPORTS_48B_ADDRESS (1<<3)
 #define EXEC_OBJECT_PINNED		 (1<<4)
+#define EXEC_OBJECT_PAD_TO_SIZE		 (1<<5)
 /* All remaining bits are MBZ and RESERVED FOR FUTURE USE */
-#define __EXEC_OBJECT_UNKNOWN_FLAGS	(-(EXEC_OBJECT_PINNED<<1))
+#define __EXEC_OBJECT_UNKNOWN_FLAGS -(EXEC_OBJECT_PAD_TO_SIZE<<1)
 	__u64 flags;
 
-	__u64 rsvd1;
+	union {
+		__u64 rsvd1;
+		__u64 pad_to_size;
+	};
 	__u64 rsvd2;
 };