drm/mediatek: Add display merge async reset control

Add merge async reset control in mtk_merge_stop. Async hw doesn't do self
reset on each sof signal(start of frame), so need to reset the async to
clear the hw status for the next merge start.
Signed-off-by: Nancy.Lin <nancy.lin@mediatek.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Tested-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Tested-by: Bo-Chen Chen <rex-bc.chen@mediatek.com>
Link: https://patchwork.kernel.org/project/linux-mediatek/patch/20220620091930.27797-8-nancy.lin@mediatek.com/Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>

drivers/gpu/drm/mediatek/mtk_disp_merge.c

@@ -8,6 +8,7 @@
 #include <linux/of_device.h>
 #include <linux/of_irq.h>
 #include <linux/platform_device.h>
+#include <linux/reset.h>
 #include <linux/soc/mediatek/mtk-cmdq.h>
 
 #include "mtk_drm_ddp_comp.h"
@@ -67,6 +68,7 @@ struct mtk_disp_merge {
 	struct cmdq_client_reg		cmdq_reg;
 	bool				fifo_en;
 	bool				mute_support;
+	struct reset_control		*reset_ctl;
 };
 
 void mtk_merge_start(struct device *dev)
@@ -101,6 +103,9 @@ void mtk_merge_stop_cmdq(struct device *dev, struct cmdq_pkt *cmdq_pkt)
 
 	mtk_ddp_write(cmdq_pkt, 0, &priv->cmdq_reg, priv->regs,
 		      DISP_REG_MERGE_CTRL);
+
+	if (priv->async_clk)
+		reset_control_reset(priv->reset_ctl);
 }
 
 static void mtk_merge_fifo_setting(struct mtk_disp_merge *priv,
@@ -264,6 +269,12 @@ static int mtk_disp_merge_probe(struct platform_device *pdev)
 		return PTR_ERR(priv->async_clk);
 	}
 
+	if (priv->async_clk) {
+		priv->reset_ctl = devm_reset_control_get_optional_exclusive(dev, NULL);
+		if (IS_ERR(priv->reset_ctl))
+			return PTR_ERR(priv->reset_ctl);
+	}
+
 #if IS_REACHABLE(CONFIG_MTK_CMDQ)
 	ret = cmdq_dev_get_client_reg(dev, &priv->cmdq_reg, 0);
 	if (ret)