drm/i915: Warn in debug builds of incorrect usages of ptr_pack_bits

GEM_BUG_ON if the packed bits do not fit into the specified width.

v2: Avoid using the macro argument twice.
v3: Drop unnecessary braces. (Joonas)

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> (v1)
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171103090538.14474-1-tvrtko.ursulin@linux.intel.com

diff --git a/drivers/gpu/drm/i915/i915_utils.h b/drivers/gpu/drm/i915/i915_utils.h
index af3d7cc..8d07764 100644 (file)
--- a/drivers/gpu/drm/i915/i915_utils.h
+++ b/drivers/gpu/drm/i915/i915_utils.h
@@ -83,8 +83,11 @@
        (typeof(ptr))(__v & -BIT(n));                                   \
 })
 
-#define ptr_pack_bits(ptr, bits, n)                                    \
-       ((typeof(ptr))((unsigned long)(ptr) | (bits)))
+#define ptr_pack_bits(ptr, bits, n) ({                                 \
+       unsigned long __bits = (bits);                                  \
+       GEM_BUG_ON(__bits & -BIT(n));                                   \
+       ((typeof(ptr))((unsigned long)(ptr) | __bits));                 \
+})
 
 #define page_mask_bits(ptr) ptr_mask_bits(ptr, PAGE_SHIFT)
 #define page_unmask_bits(ptr) ptr_unmask_bits(ptr, PAGE_SHIFT)