drm/mediatek: mtk_hdmi_common: Make CEC support optional

In preparation for adding a new driver for HDMIv2, for which CEC
is not strictly required, change the of_get_compatible_child()
failure error to -EOPNOTSUPP to be able to differentiate between
error conditions in mtk_hdmi_dt_parse_pdata().

In that case, if -EOPNOTSUPP is returned, this driver will print
an informative message saying that CEC support is unavailable,
as the devicetree node for that was not found, but after that,
function mtk_hdmi_dt_parse_pdata() will not return error to
the caller.

This will not change functionality of the mtk_hdmi (v1) driver
as that is still checking whether CEC is present and, if not,
will fail probing with an error saying that CEC is required
by HDMIv1.

Reviewed-by: CK Hu <ck.hu@mediatek.com>
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Louis-Alexis Eyraud <louisalexis.eyraud@collabora.com>
Link: https://patchwork.kernel.org/project/linux-mediatek/patch/20251023-mediatek-drm-hdmi-v2-v11-5-7873ec4a1edf@collabora.com/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>

Author: AngeloGioacchino Del Regno

drivers/gpu/drm/mediatek/mtk_hdmi_common.c

@@ -261,12 +261,11 @@ static int mtk_hdmi_get_cec_dev(struct mtk_hdmi *hdmi, struct device *dev, struc
 	/* The CEC module handles HDMI hotplug detection */
 	cec_np = of_get_compatible_child(np->parent, "mediatek,mt8173-cec");
 	if (!cec_np)
-		return dev_err_probe(dev, -EINVAL, "Failed to find CEC node\n");
+		return dev_err_probe(dev, -EOPNOTSUPP, "Failed to find CEC node\n");
 
 	cec_pdev = of_find_device_by_node(cec_np);
 	if (!cec_pdev) {
-		dev_err(hdmi->dev, "Waiting for CEC device %pOF\n",
-			cec_np);
+		dev_err(hdmi->dev, "Waiting for CEC device %pOF\n", cec_np);
 		of_node_put(cec_np);
 		return -EPROBE_DEFER;
 	}
@@ -335,7 +334,9 @@ static int mtk_hdmi_dt_parse_pdata(struct mtk_hdmi *hdmi, struct platform_device
 		return ret;
 
 	ret = mtk_hdmi_get_cec_dev(hdmi, dev, np);
-	if (ret)
+	if (ret == -EOPNOTSUPP)
+		dev_info(dev, "CEC support unavailable: node not found\n");
+	else if (ret)
 		return ret;
 
 	return 0;