drm/mediatek: Fix missing configuration flags in mtk_crtc_ddp_config()

In mtk_crtc_ddp_config(), mtk_crtc will use some configuration flags to
generate instructions to cmdq_handle, such as:
  state->pending_config
  mtk_crtc->pending_planes
  plane_state->pending.config
  mtk_crtc->pending_async_planes
  plane_state->pending.async_config

These configuration flags may be set to false when a GCE IRQ comes calling
ddp_cmdq_cb(). This may result in missing prepare instructions,
especially if mtk_crtc_update_config() with the flase need_vblank (no need
to wait for vblank) cases.

Therefore, the mtk_crtc->config_updating flag is set at the beginning of
mtk_crtc_update_config() to ensure that these configuration flags won't be
changed when the mtk_crtc_ddp_config() is preparing instructions.
But somehow the ddp_cmdq_cb() didn't use the mtk_crtc->config_updating
flag to prevent those pending config flags from being cleared.

To avoid missing the configuration when generating the config instruction,
the config_updating flag should be added into ddp_cmdq_cb() and be
protected with spin_lock.

Fixes: 7f82d9c4 ("drm/mediatek: Clear pending flag when cmdq packet is done")
Signed-off-by: Jason-JH.Lin <jason-jh.lin@mediatek.com>
Reviewed-by: CK Hu <ck.hu@mediatek.com>
Reviewed-by: Fei Shao <fshao@chromium.org>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20240827-drm-fixup-0819-v3-1-4761005211ec@mediatek.com/
Link: https://patchwork.kernel.org/project/dri-devel/patch/20240827-drm-fixup-0819-v3-2-4761005211ec@mediatek.com/Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>

drivers/gpu/drm/mediatek/mtk_crtc.c

@@ -69,6 +69,8 @@ struct mtk_crtc {
 	/* lock for display hardware access */
 	struct mutex			hw_lock;
 	bool				config_updating;
+	/* lock for config_updating to cmd buffer */
+	spinlock_t			config_lock;
 };
 
 struct mtk_crtc_state {
@@ -106,11 +108,16 @@ static void mtk_crtc_finish_page_flip(struct mtk_crtc *mtk_crtc)
 
 static void mtk_drm_finish_page_flip(struct mtk_crtc *mtk_crtc)
 {
+	unsigned long flags;
+
 	drm_crtc_handle_vblank(&mtk_crtc->base);
+
+	spin_lock_irqsave(&mtk_crtc->config_lock, flags);
 	if (!mtk_crtc->config_updating && mtk_crtc->pending_needs_vblank) {
 		mtk_crtc_finish_page_flip(mtk_crtc);
 		mtk_crtc->pending_needs_vblank = false;
 	}
+	spin_unlock_irqrestore(&mtk_crtc->config_lock, flags);
 }
 
 static void mtk_crtc_destroy(struct drm_crtc *crtc)
@@ -270,12 +277,19 @@ static void ddp_cmdq_cb(struct mbox_client *cl, void *mssg)
 	struct mtk_crtc *mtk_crtc = container_of(cmdq_cl, struct mtk_crtc, cmdq_client);
 	struct mtk_crtc_state *state;
 	unsigned int i;
+	unsigned long flags;
 
 	if (data->sta < 0)
 		return;
 
 	state = to_mtk_crtc_state(mtk_crtc->base.state);
 
+	spin_lock_irqsave(&mtk_crtc->config_lock, flags);
+	if (mtk_crtc->config_updating) {
+		spin_unlock_irqrestore(&mtk_crtc->config_lock, flags);
+		goto ddp_cmdq_cb_out;
+	}
+
 	state->pending_config = false;
 
 	if (mtk_crtc->pending_planes) {
@@ -302,6 +316,10 @@ static void ddp_cmdq_cb(struct mbox_client *cl, void *mssg)
 		mtk_crtc->pending_async_planes = false;
 	}
 
+	spin_unlock_irqrestore(&mtk_crtc->config_lock, flags);
+
+ddp_cmdq_cb_out:
+
 	mtk_crtc->cmdq_vblank_cnt = 0;
 	wake_up(&mtk_crtc->cb_blocking_queue);
 }
@@ -531,9 +549,14 @@ static void mtk_crtc_update_config(struct mtk_crtc *mtk_crtc, bool needs_vblank)
 	struct mtk_drm_private *priv = crtc->dev->dev_private;
 	unsigned int pending_planes = 0, pending_async_planes = 0;
 	int i;
+	unsigned long flags;
 
 	mutex_lock(&mtk_crtc->hw_lock);
+
+	spin_lock_irqsave(&mtk_crtc->config_lock, flags);
 	mtk_crtc->config_updating = true;
+	spin_unlock_irqrestore(&mtk_crtc->config_lock, flags);
+
 	if (needs_vblank)
 		mtk_crtc->pending_needs_vblank = true;
 
@@ -587,7 +610,10 @@ static void mtk_crtc_update_config(struct mtk_crtc *mtk_crtc, bool needs_vblank)
 		mbox_client_txdone(mtk_crtc->cmdq_client.chan, 0);
 	}
 #endif
+	spin_lock_irqsave(&mtk_crtc->config_lock, flags);
 	mtk_crtc->config_updating = false;
+	spin_unlock_irqrestore(&mtk_crtc->config_lock, flags);
+
 	mutex_unlock(&mtk_crtc->hw_lock);
 }
 
@@ -1030,6 +1056,7 @@ int mtk_crtc_create(struct drm_device *drm_dev, const unsigned int *path,
 		drm_mode_crtc_set_gamma_size(&mtk_crtc->base, gamma_lut_size);
 	drm_crtc_enable_color_mgmt(&mtk_crtc->base, 0, has_ctm, gamma_lut_size);
 	mutex_init(&mtk_crtc->hw_lock);
+	spin_lock_init(&mtk_crtc->config_lock);
 
 #if IS_REACHABLE(CONFIG_MTK_CMDQ)
 	i = priv->mbox_index++;