From 426960bed3217f72a1b7bb94f084d79cc616ec0f Mon Sep 17 00:00:00 2001 From: Chris Wilson 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 Testcase: igt/gem_busy Cc: Tvrtko Ursulin Cc: Daniel Vetter Reviewed-by: Tvrtko Ursulin Acked-by: Daniel Vetter 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') diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h index acf2102..6a19371 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; }; -- cgit v1.1