drm/i915: give stolen_usable_size a more suitable home

Kick it out of i915_ggtt and keep it grouped with dsm and dsm_reserved,
where it makes the most sense.

Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171211151822.20953-9-matthew.auld@intel.com
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 7945af0..d71e59e 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2254,7 +2254,7 @@ struct drm_i915_private {
 	/**
 	 * Data Stolen Memory - aka "i915 stolen memory" gives us the start and
 	 * end of stolen which we can optionally use to create GEM objects
-	 * backed by stolen memory. Note that ggtt->stolen_usable_size tells us
+	 * backed by stolen memory. Note that stolen_usable_size tells us
 	 * exactly how much of this we are actually allowed to use, given that
 	 * some portion of it is in fact reserved for use by hardware functions.
 	 */
@@ -2264,6 +2264,17 @@ struct drm_i915_private {
 	 */
 	struct resource dsm_reserved;
 
+	/*
+	 * Stolen memory is segmented in hardware with different portions
+	 * offlimits to certain functions.
+	 *
+	 * The drm_mm is initialised to the total accessible range, as found
+	 * from the PCI config. On Broadwell+, this is further restricted to
+	 * avoid the first page! The upper end of stolen memory is reserved for
+	 * hardware functions and similarly removed from the accessible range.
+	 */
+	u32 stolen_usable_size;	/* Total size minus reserved ranges */
+
 	void __iomem *regs;
 
 	struct intel_uncore uncore;