[Intel-gfx] [PATCH 1/2] drm/i915: compile-time consistency check on __EXEC_OBJECT flags

[Dave Gordon]

Two different sets of flag bits are stored in the 'flags' member of a
'struct drm_i915_gem_exec_object2', and they're defined in two different
source files, increasing the risk of an accidental clash.

Some flags in this field are supplied by the user; these are defined in
i915_drm.h, and they start from the LSB and work up.

Other flags are defined in i915_gem_execbuffer, for internal use within
that file only; they start from the MSB and work down.

So here we add a compile-time check that the two sets of flags do not
overlap, which would cause all sorts of confusion.

Signed-off-by: Dave Gordon <david.s.gordon at intel.com>
---
 drivers/gpu/drm/i915/i915_gem_execbuffer.c | 12 ++++++++----
 include/uapi/drm/i915_drm.h                | 11 ++++++-----
 2 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
index 1978633..1bb1f25 100644
--- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
+++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
@@ -34,10 +34,11 @@
 #include <linux/dma_remapping.h>
 #include <linux/uaccess.h>
 
-#define  __EXEC_OBJECT_HAS_PIN (1<<31)
-#define  __EXEC_OBJECT_HAS_FENCE (1<<30)
-#define  __EXEC_OBJECT_NEEDS_MAP (1<<29)
-#define  __EXEC_OBJECT_NEEDS_BIAS (1<<28)
+#define  __EXEC_OBJECT_HAS_PIN		(1<<31)
+#define  __EXEC_OBJECT_HAS_FENCE	(1<<30)
+#define  __EXEC_OBJECT_NEEDS_MAP	(1<<29)
+#define  __EXEC_OBJECT_NEEDS_BIAS	(1<<28)
+#define  __EXEC_OBJECT_INTERNAL_FLAGS (0xf<<28) /* all of the above */
 
 #define BATCH_OFFSET_BIAS (256*1024)
 
@@ -1007,6 +1008,9 @@ static bool only_mappable_for_reloc(unsigned int flags)
 	unsigned invalid_flags;
 	int i;
 
+	/* INTERNAL flags must not overlap with external ones */
+	BUILD_BUG_ON(__EXEC_OBJECT_INTERNAL_FLAGS & ~__EXEC_OBJECT_UNKNOWN_FLAGS);
+
 	invalid_flags = __EXEC_OBJECT_UNKNOWN_FLAGS;
 	if (USES_FULL_PPGTT(dev))
 		invalid_flags |= EXEC_OBJECT_NEEDS_GTT;
diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
index d7e81a3..51b9360 100644
--- a/include/uapi/drm/i915_drm.h
+++ b/include/uapi/drm/i915_drm.h
@@ -698,12 +698,13 @@ struct drm_i915_gem_exec_object2 {
 	 */
 	__u64 offset;
 
-#define EXEC_OBJECT_NEEDS_FENCE (1<<0)
-#define EXEC_OBJECT_NEEDS_GTT	(1<<1)
-#define EXEC_OBJECT_WRITE	(1<<2)
+#define EXEC_OBJECT_NEEDS_FENCE		 (1<<0)
+#define EXEC_OBJECT_NEEDS_GTT		 (1<<1)
+#define EXEC_OBJECT_WRITE		 (1<<2)
 #define EXEC_OBJECT_SUPPORTS_48B_ADDRESS (1<<3)
-#define EXEC_OBJECT_PINNED	(1<<4)
-#define __EXEC_OBJECT_UNKNOWN_FLAGS -(EXEC_OBJECT_PINNED<<1)
+#define EXEC_OBJECT_PINNED		 (1<<4)
+/* All remaining bits are MBZ and RESERVED FOR FUTURE USE */
+#define __EXEC_OBJECT_UNKNOWN_FLAGS	(-(EXEC_OBJECT_PINNED<<1))
 	__u64 flags;
 
 	__u64 rsvd1;
-- 
1.9.1