drm/msm/mdp5: don't pre-reserve LM's if no dual-dsi

If there is only a single DSI interface, don't reserve the first two
layer-mixers for the dual-DSI use-case.

This was causing problems for WB, not being able to assign a LM, on
8x16, which has only two LM's and a single DSI.
Signed-off-by: Rob Clark <robdclark@gmail.com>

drivers/gpu/drm/msm/disp/mdp5/mdp5_ctl.c

@@ -691,6 +691,7 @@ struct mdp5_ctl_manager *mdp5_ctlm_init(struct drm_device *dev,
 	struct mdp5_ctl_manager *ctl_mgr;
 	const struct mdp5_cfg_hw *hw_cfg = mdp5_cfg_get_hw_config(cfg_hnd);
 	int rev = mdp5_cfg_get_hw_rev(cfg_hnd);
+	unsigned dsi_cnt = 0;
 	const struct mdp5_ctl_block *ctl_cfg = &hw_cfg->ctl;
 	unsigned long flags;
 	int c, ret;
@@ -740,7 +741,10 @@ struct mdp5_ctl_manager *mdp5_ctlm_init(struct drm_device *dev,
 	 * only write into CTL0's FLUSH register) to keep two DSI pipes in sync.
 	 * Single FLUSH is supported from hw rev v3.0.
 	 */
-	if (rev >= 3) {
+	for (c = 0; c < ARRAY_SIZE(hw_cfg->intf.connect); c++)
+		if (hw_cfg->intf.connect[c] == INTF_DSI)
+			dsi_cnt++;
+	if ((rev >= 3) && (dsi_cnt > 1)) {
 		ctl_mgr->single_flush_supported = true;
 		/* Reserve CTL0/1 for INTF1/2 */
 		ctl_mgr->ctls[0].status |= CTL_STAT_BOOKED;