drm/i915/fbc: Limit cfb to the first 256MiB of stolen on g4x+

Since g4x the CFB base only takes a 28bit offset into stolen.
Not sure if the CFB is allowed to start below that limit but
then extend beyond it. Let's assume not and just restrict the
allocation to the first 256MiB (in the unlikely case
we have more stolen than that).

v2: s/BIT/BIT_ULL/ (Chris)

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200714201945.18959-1-ville.syrjala@linux.intel.comReviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

drivers/gpu/drm/i915/display/intel_fbc.c

@@ -424,6 +424,14 @@ static void intel_fbc_deactivate(struct drm_i915_private *dev_priv,
 	fbc->no_fbc_reason = reason;
 }
 
+static u64 intel_fbc_cfb_base_max(struct drm_i915_private *i915)
+{
+	if (INTEL_GEN(i915) >= 5 || IS_G4X(i915))
+		return BIT_ULL(28);
+	else
+		return BIT_ULL(32);
+}
+
 static int find_compression_threshold(struct drm_i915_private *dev_priv,
 				      struct drm_mm_node *node,
 				      unsigned int size,
@@ -442,6 +450,8 @@ static int find_compression_threshold(struct drm_i915_private *dev_priv,
 	else
 		end = U64_MAX;
 
+	end = min(end, intel_fbc_cfb_base_max(dev_priv));
+
 	/* HACK: This code depends on what we will do in *_enable_fbc. If that
 	 * code changes, this code needs to change as well.
 	 *