From 426960bed3217f72a1b7bb94f084d79cc616ec0f Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Fri, 15 Jan 2016 16:51:46 +0000
Subject: drm/i915: Seal busy-ioctl uABI and prevent leaking of internal ids
Tvrtko was looking through the execbuffer-ioctl and noticed that the
uABI was tightly coupled to our internal engine identifiers. Close
inspection also revealed that we leak those internal engine identifiers
through the busy-ioctl, and those internal identifiers already do not
match the user identifiers. Fortuitiously, there is only one user of the
set of busy rings from the busy-ioctl, and they only wish to choose
between the RENDER and the BLT engines.
Let's fix the userspace ABI while we still can.
v2: Update the uAPI documentation to explain the identifiers.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Testcase: igt/gem_busy
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1452876706-21620-1-git-send-email-chris@chris-wilson.co.uk
---
include/uapi/drm/i915_drm.h | 33 +++++++++++++++++++++++++++++----
1 file changed, 29 insertions(+), 4 deletions(-)
(limited to 'include/uapi/drm')
diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
index acf21026c78a..6a19371391fa 100644
--- a/include/uapi/drm/i915_drm.h
+++ b/include/uapi/drm/i915_drm.h
@@ -812,10 +812,35 @@ struct drm_i915_gem_busy {
/** Handle of the buffer to check for busy */
__u32 handle;
- /** 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)
+ /** Return busy status
+ *
+ * A return of 0 implies that the object is idle (after
+ * having flushed any pending activity), and a non-zero return that
+ * the object is still in-flight on the GPU. (The GPU has not yet
+ * signaled completion for all pending requests that reference the
+ * object.)
+ *
+ * The returned dword is split into two fields to indicate both
+ * the engines on which the object is being read, and the
+ * engine on which it is currently being written (if any).
+ *
+ * The low word (bits 0:15) indicate if the object is being written
+ * to by any engine (there can only be one, as the GEM implicit
+ * synchronisation rules force writes to be serialised). Only the
+ * engine for the last write is reported.
+ *
+ * The high word (bits 16:31) are a bitmask of which engines are
+ * currently reading from the object. Multiple engines may be
+ * reading from the object simultaneously.
+ *
+ * The value of each engine is the same as specified in the
+ * EXECBUFFER2 ioctl, i.e. I915_EXEC_RENDER, I915_EXEC_BSD etc.
+ * Note I915_EXEC_DEFAULT is a symbolic value and is mapped to
+ * the I915_EXEC_RENDER engine for execution, and so it is never
+ * reported as active itself. Some hardware may have parallel
+ * execution engines, e.g. multiple media engines, which are
+ * mapped to the same identifier in the EXECBUFFER2 ioctl and
+ * so are not separately reported for busyness.
*/
__u32 busy;
};
--
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