drm/mediatek: dp: Avoid mutex locks if audio is not supported/enabled

If a controller (usually, eDP!) does not support audio, or audio is not
enabled because the endpoint has no audio support, it's useless to lock
a mutex only to unlock it right after because there's no .plugged_cb().

Check if the audio is supported and enabled before locking the mutex in
mtk_dp_update_plugged_status(): if not, we simply return immediately.

While at it, since the update_plugged_status_lock mutex would not be
used if the controller doesn't support audio at all, initialize it
only if `audio_supported` is true.

Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Tested-by: Chen-Yu Tsai <wenst@chromium.org>
Reviewed-by: Alexandre Mergnat <amergnat@baylibre.com>
Reviewed-by: CK Hu <ck.hu@mediatek.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20230725073234.55892-8-angelogioacchino.delregno@collabora.com/
Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>

Author: AngeloGioacchino Del Regno

drivers/gpu/drm/mediatek/mtk_dp.c

@@ -1948,6 +1948,9 @@ static int mtk_dp_dt_parse(struct mtk_dp *mtk_dp,
 
 static void mtk_dp_update_plugged_status(struct mtk_dp *mtk_dp)
 {
+	if (!mtk_dp->data->audio_supported || !mtk_dp->audio_enable)
+		return;
+
 	mutex_lock(&mtk_dp->update_plugged_status_lock);
 	if (mtk_dp->plugged_cb && mtk_dp->codec_dev)
 		mtk_dp->plugged_cb(mtk_dp->codec_dev,
@@ -2520,11 +2523,11 @@ static int mtk_dp_probe(struct platform_device *pdev)
 		return dev_err_probe(dev, ret,
 				     "failed to request mediatek dptx irq\n");
 
-	mutex_init(&mtk_dp->update_plugged_status_lock);
-
 	platform_set_drvdata(pdev, mtk_dp);
 
 	if (mtk_dp->data->audio_supported) {
+		mutex_init(&mtk_dp->update_plugged_status_lock);
+
 		ret = mtk_dp_register_audio_driver(dev);
 		if (ret) {
 			dev_err(dev, "Failed to register audio driver: %d\n",