disp: msm: sde: handle LTM switch in and out of dual pipe merge mode

When LTM is switching on/off, merge_mode bit value gets toggled between
0x1 (dual pipe merge configuration) and 0x0 (single pipe configuration).
It is illegal to reconfigure LTM to/from dual-pipe merge mode before
both LTM instances have completed their current workloads. This change
adds support to disable merge_mode one frame after histogram is disabled
to make sure both hardware instances are completely idle and avoid
corrupted histogram data collection.

Change-Id: I9a6b5cbfb69e8af7936749e57fe7c8f7c2703b95
Signed-off-by: Ping Li <pingli@codeaurora.org>

msm/sde/sde_crtc.h

@@ -312,6 +312,7 @@ struct sde_frame_data {
  * @ltm_buf_free    : list of LTM buffers that are available
  * @ltm_buf_busy    : list of LTM buffers that are been used by HW
  * @ltm_hist_en     : flag to indicate whether LTM hist is enabled or not
+ * @ltm_merge_clear_pending : flag indicates merge mode bit needs to be cleared
  * @ltm_buffer_lock : muttx to protect ltm_buffers allcation and free
  * @ltm_lock        : Spinlock to protect ltm buffer_cnt, hist_en and ltm lists
  * @needs_hw_reset  : Initiate a hw ctl reset
@@ -407,6 +408,7 @@ struct sde_crtc {
 	struct list_head ltm_buf_free;
 	struct list_head ltm_buf_busy;
 	bool ltm_hist_en;
+	bool ltm_merge_clear_pending;
 	struct drm_msm_ltm_cfg_param ltm_cfg;
 	struct mutex ltm_buffer_lock;
 	spinlock_t ltm_lock;