drm/i915/display: consider DG2_RC_CCS_CC when migrating buffers

For these types of display buffers, we need to able to CPU access some
part of the backing memory in prepare_plane_clear_colors(). As a result
we need to ensure we always place in the mappable part of lmem, which
becomes necessary on small-bar systems.

v2(Nirmoy & Ville):
 - Add some commentary for why we need to CPU access the buffer.
 - Split out the other changes, so we just consider the display change
   here.
v3:
 - Handle this in the dpt path.
v4(Ville):
 - Drop the intel_fb_rc_ccs_cc_plane() sanity check in
   pin_and_fence_fb_obj(), since we can also trigger this on DG1 it
   seems.

Fixes: eb1c535f ("drm/i915: turn on small BAR support")
Reported-by: Jianshui Yu <jianshui.yu@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Nirmoy Das <nirmoy.das@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Acked-by: Nirmoy Das <nirmoy.das@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221004131916.233474-4-matthew.auld@intel.com

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

@@ -50,7 +50,18 @@ intel_pin_fb_obj_dpt(struct drm_framebuffer *fb,
 			continue;
 
 		if (HAS_LMEM(dev_priv)) {
-			ret = i915_gem_object_migrate(obj, &ww, INTEL_REGION_LMEM_0);
+			unsigned int flags = obj->flags;
+
+			/*
+			 * For this type of buffer we need to able to read from the CPU
+			 * the clear color value found in the buffer, hence we need to
+			 * ensure it is always in the mappable part of lmem, if this is
+			 * a small-bar device.
+			 */
+			if (intel_fb_rc_ccs_cc_plane(fb) >= 0)
+				flags &= ~I915_BO_ALLOC_GPU_ONLY;
+			ret = __i915_gem_object_migrate(obj, &ww, INTEL_REGION_LMEM_0,
+							flags);
 			if (ret)
 				continue;
 		}