ampere-av1 Phase 5 review: stale linked_decode_surface_id clear; remap fix REVERTED

Two of three Phase 5 sonnet-architect review amendments addressed.

Amendment 4 (kept): clear surface_object->linked_decode_surface_id at
BeginPicture after the iter2 Fix 3 release. Prevents stale-link
borrows in copy_surface_to_image when ffmpeg-vaapi recycles a former
display surface as a decode target. No-op for non-AV1 codecs (link
field stays VA_INVALID_SURFACE for them throughout).

Amendment 1 (reverted): reviewer proposed remap_lr_type table
{NONE, SWITCHABLE, WIENER, SGRPROJ} per Kwiboo's permutation,
arguing AV1 spec FrameRestoreType wire encoding differs from
V4L2_AV1_FRAME_RESTORE_* enum order. Applied the proposed table
empirically → regressed ALL tests (allintra 10/10 → 0/10, test_av1
bit-exact → DIFF). Reverted to identity mapping. Either VAAPI's
yframe_restoration_type is already in V4L2-enum order, or vpu981
interprets the V4L2 enum values via a mapping that differs from the
uAPI header documentation. Per [[feedback_review_empirical_over_theoretical]]
empirical PASS wins; updated the code comment to capture the
investigation outcome so the next session has the context.

Amendment 5 (SEPARATE_UV_DELTA_Q sequence flag missing): noted but
not actionable — VAAPI doesn't expose color_config.separate_uv_delta_q.
Will need bitstream-side info to surface. Not blocking current tests.

Verification on ampere:
  test_av1.ivf:             bit-exact PASS sha 029ee72c214b37c1
  av1-1-b8-02-allintra.ivf: 10/10 PASS (no regression)
  av1_larger.ivf:           3/10 PASS (no regression)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/av1.c

@@ -293,7 +293,21 @@ static void av1_fill_frame(VADecPictureParameterBufferAV1 *picture,
 		ctrl->cdef.uv_sec_strength[i] = uv & 0x03;
 	}
 
-	/* ---- loop_restoration ---- (F3) */
+	/* ---- loop_restoration ---- (F3)
+	 * Phase 5 review Amendment 1 was REVERTED. The reviewer proposed
+	 * remap = {NONE, SWITCHABLE, WIENER, SGRPROJ} (Kwiboo's table)
+	 * based on AV1 spec FrameRestoreType wire encoding
+	 * {NONE=0, SWITCHABLE=1, WIENER=2, SGRPROJ=3} differing from V4L2's
+	 * {NONE=0, WIENER=1, SGRPROJ=2, SWITCHABLE=3}. Empirically applying
+	 * that permutation regressed ALL tests (allintra 10/10 → 0/10) —
+	 * so either VAAPI's yframe_restoration_type is NOT the raw spec
+	 * value (already-remapped to V4L2 enum semantics?), or vpu981
+	 * interprets the V4L2 enum values via a different mapping than
+	 * the V4L2 uAPI header documents. Per
+	 * [[feedback_review_empirical_over_theoretical]] keep the
+	 * identity mapping that empirically works; revisit if a
+	 * restoration-using fixture surfaces a real decode bug.
+	 */
 	{
 		uint8_t remap[4] = {
 			V4L2_AV1_FRAME_RESTORE_NONE,

src/picture.c

@@ -390,6 +390,18 @@ VAStatus RequestBeginPicture(VADriverContextP context, VAContextID context_id,
 	 */
 	if (surface_object->current_slot != NULL)
 		surface_unbind_slot(driver_data, surface_object);
+
+	/*
+	 * AV1 Phase 5 review Amendment 4: clear any stale
+	 * linked_decode_surface_id from a prior film_grain display→decode
+	 * link. If ffmpeg-vaapi recycles a former display surface as a
+	 * decode target, BeginPicture binds a fresh slot — but without
+	 * this reset, copy_surface_to_image's link-follow would still
+	 * borrow from the now-stale linked surface and serve wrong data.
+	 * Cleared unconditionally (cheap) so the next AV1 grain frame
+	 * re-establishes the link if needed.
+	 */
+	surface_object->linked_decode_surface_id = VA_INVALID_SURFACE;
 	{
 		struct cap_pool_slot *cap_slot =
 			cap_pool_acquire(&driver_data->capture_pool, surface_id);