drm/mediatek: Turn off the layers with zero width or height

We found that IGT (Intel GPU Tool) will try to commit layers with
zero width or height and lead to undefined behaviors in hardware.
Disable the layers in such a situation.

Fixes: 453c3364 ("drm/mediatek: Add ovl_adaptor support for MT8195")
Fixes: d886c000 ("drm/mediatek: Add ETHDR support for MT8195")
Reviewed-by: CK Hu <ck.hu@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Fixes: 119f5173 ("drm/mediatek: Add DRM Driver for Mediatek SoC MT8173.")
Signed-off-by: Hsiao Chien Sung <shawn.sung@mediatek.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20240620-igt-v3-6-a9d62d2e2c7e@mediatek.com/Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>

drivers/gpu/drm/mediatek/mtk_disp_ovl_adaptor.c

@@ -158,7 +158,7 @@ void mtk_ovl_adaptor_layer_config(struct device *dev, unsigned int idx,
 	merge = ovl_adaptor->ovl_adaptor_comp[OVL_ADAPTOR_MERGE0 + idx];
 	ethdr = ovl_adaptor->ovl_adaptor_comp[OVL_ADAPTOR_ETHDR0];
 
-	if (!pending->enable) {
+	if (!pending->enable || !pending->width || !pending->height) {
 		mtk_merge_stop_cmdq(merge, cmdq_pkt);
 		mtk_mdp_rdma_stop(rdma_l, cmdq_pkt);
 		mtk_mdp_rdma_stop(rdma_r, cmdq_pkt);

drivers/gpu/drm/mediatek/mtk_ethdr.c

@@ -160,7 +160,12 @@ void mtk_ethdr_layer_config(struct device *dev, unsigned int idx,
 	if (idx >= 4)
 		return;
 
-	if (!pending->enable) {
+	if (!pending->enable || !pending->width || !pending->height) {
+		/*
+		 * instead of disabling layer with MIX_SRC_CON directly
+		 * set the size to 0 to avoid screen shift due to mixer
+		 * mode switch (hardware behavior)
+		 */
 		mtk_ddp_write(cmdq_pkt, 0, &mixer->cmdq_base, mixer->regs, MIX_L_SRC_SIZE(idx));
 		return;
 	}