drm/i915: Agnostic INTEL_INFO

Adapt the macro so that we can pass either the struct drm_device or the
struct drm_i915_private pointers and get the answer we want. Over time,
my plan is to convert all users over to using drm_i915_private and so
trimming down the pointer dance. Having spent a few hours chasing that
goal and achieved over 8k of object code saving, it appears to be a
worthwhile target. This interim macro allows us to slowly convert over.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
[danvet: Drop the (struct drm_device *) cast per the m-l discussion.
Also explain the seemingly unecessary first cast.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_dma.c

@@ -1596,6 +1596,9 @@ 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));
+
 	dev_priv = kzalloc(sizeof(*dev_priv), GFP_KERNEL);
 	if (dev_priv == NULL)
 		return -ENOMEM;

drivers/gpu/drm/i915/i915_drv.h

@@ -1981,7 +1981,10 @@ struct drm_i915_cmd_table {
 	int count;
 };
 
-#define INTEL_INFO(p) 	(&to_i915(p)->info)
+/* 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 INTEL_INFO(p) 	(&__I915__(p)->info)
 #define INTEL_DEVID(p)	(INTEL_INFO(p)->device_id)
 
 #define IS_I830(dev)		(INTEL_DEVID(dev) == 0x3577)