drm/i915/migrate: fix corner case in CCS aux copying

In the case of lmem -> lmem transfers, which is currently only possible
with small-bar systems, we need to ensure we copy the CCS aux state
as-is, rather than nuke it. This should fix some nasty display
corruption sometimes seen on DG2 small-bar systems, when also using
DG2_RC_CCS_CC for the surface.

Fixes: e3afc690 ("drm/i915/display: consider DG2_RC_CCS_CC when migrating buffers")
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Nirmoy Das <nirmoy.das@intel.com>
Cc: Andrzej Hajda <andrzej.hajda@intel.com>
Cc: Shuicheng Lin <shuicheng.lin@intel.com>
Reviewed-by: Nirmoy Das <nirmoy.das@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221212171958.82593-1-matthew.auld@intel.com

drivers/gpu/drm/i915/gt/intel_migrate.c

@@ -839,14 +839,35 @@ intel_context_migrate_copy(struct intel_context *ce,
 			if (err)
 				goto out_rq;
 
+			if (src_is_lmem) {
+				/*
+				 * If the src is already in lmem, then we must
+				 * be doing an lmem -> lmem transfer, and so
+				 * should be safe to directly copy the CCS
+				 * state. In this case we have either
+				 * initialised the CCS aux state when first
+				 * clearing the pages (since it is already
+				 * allocated in lmem), or the user has
+				 * potentially populated it, in which case we
+				 * need to copy the CCS state as-is.
+				 */
+				err = emit_copy_ccs(rq,
+						    dst_offset, INDIRECT_ACCESS,
+						    src_offset, INDIRECT_ACCESS,
+						    len);
+			} else {
 				/*
-			 * While we can't always restore/manage the CCS state,
-			 * we still need to ensure we don't leak the CCS state
-			 * from the previous user, so make sure we overwrite it
-			 * with something.
+				 * While we can't always restore/manage the CCS
+				 * state, we still need to ensure we don't leak
+				 * the CCS state from the previous user, so make
+				 * sure we overwrite it with something.
 				 */
-			err = emit_copy_ccs(rq, dst_offset, INDIRECT_ACCESS,
-					    dst_offset, DIRECT_ACCESS, len);
+				err = emit_copy_ccs(rq,
+						    dst_offset, INDIRECT_ACCESS,
+						    dst_offset, DIRECT_ACCESS,
+						    len);
+			}
+
 			if (err)
 				goto out_rq;