[Intel-gfx] [PATCH] drm/i915: Replace __I915__ with typesafe variant

[Chris Wilson]

Ville pointed out the GCCism __builtin_types_compatible_p() that we
could use to replace our heavily casted presumption __I915__ macro that
was based on comparing struct sizes.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/i915/i915_dma.c |  3 ---
 drivers/gpu/drm/i915/i915_drv.h | 12 ++++++++++--
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
index 5e3b1390ac5c..b2e4dbcb77ae 100644
--- a/drivers/gpu/drm/i915/i915_dma.c
+++ b/drivers/gpu/drm/i915/i915_dma.c
@@ -1582,9 +1582,6 @@ int i915_driver_load(struct drm_device *dev, unsigned long flags)
 	if (!drm_core_check_feature(dev, DRIVER_MODESET) && !dev->agp)
 		return -EINVAL;
 
-	/* For the ugly agnostic INTEL_INFO macro */
-	BUILD_BUG_ON(sizeof(*dev_priv) == sizeof(*dev));
-
 	BUILD_BUG_ON(I915_NUM_RINGS >= (1 << I915_NUM_RING_BITS));
 
 	dev_priv = kzalloc(sizeof(*dev_priv), GFP_KERNEL);
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index d1513e6ea50d..b6dcbf79b31c 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2081,8 +2081,16 @@ struct drm_i915_cmd_table {
 };
 
 /* Note that the (struct drm_i915_private *) cast is just to shut up gcc. */
-#define __I915__(p)	((sizeof(*(p)) == sizeof(struct drm_i915_private)) ? \
-			 (struct drm_i915_private *)(p) : to_i915(p))
+#define __I915__(p) ({ \
+	struct drm_i915_private *__p; \
+	if (__builtin_types_compatible_p(typeof(*p), struct drm_i915_private)) \
+		__p = (struct drm_i915_private *)p; \
+	else if (__builtin_types_compatible_p(typeof(*p), struct drm_device)) \
+		__p = to_i915((struct drm_device *)p); \
+	else \
+		BUILD_BUG(); \
+	__p; \
+})
 #define INTEL_INFO(p) 	(&__I915__(p)->info)
 #define INTEL_DEVID(p)	(INTEL_INFO(p)->device_id)
 
-- 
2.1.0.rc1