drm/msms/dp: fixed link clock divider bits be over written in BPC unknown case

Since the value of DP_TEST_BIT_DEPTH_8 is already left shifted, in the
BPC unknown case, the additional shift causes spill over to the other
bits of the [DP_CONFIGURATION_CTRL] register.
Fix this by changing the return value of dp_link_get_test_bits_depth()
in the BPC unknown case to (DP_TEST_BIT_DEPTH_8 >> DP_TEST_BIT_DEPTH_SHIFT).

Fixes: c943b494 ("drm/msm/dp: add displayPort driver support")
Signed-off-by: Kuogee Hsieh <quic_khsieh@quicinc.com>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/573989/
Link: https://lore.kernel.org/r/1704917931-30133-1-git-send-email-quic_khsieh@quicinc.com
[quic_abhinavk@quicinc.com: fix minor checkpatch warning to align with opening braces]
Signed-off-by: Abhinav Kumar <quic_abhinavk@quicinc.com>

drivers/gpu/drm/msm/dp/dp_ctrl.c

@@ -135,11 +135,6 @@ static void dp_ctrl_config_ctrl(struct dp_ctrl_private *ctrl)
 	tbd = dp_link_get_test_bits_depth(ctrl->link,
 			ctrl->panel->dp_mode.bpp);
 
-	if (tbd == DP_TEST_BIT_DEPTH_UNKNOWN) {
-		pr_debug("BIT_DEPTH not set. Configure default\n");
-		tbd = DP_TEST_BIT_DEPTH_8;
-	}
-
 	config |= tbd << DP_CONFIGURATION_CTRL_BPC_SHIFT;
 
 	/* Num of Lanes */

drivers/gpu/drm/msm/dp/dp_link.c

@@ -1179,6 +1179,9 @@ void dp_link_reset_phy_params_vx_px(struct dp_link *dp_link)
 u32 dp_link_get_test_bits_depth(struct dp_link *dp_link, u32 bpp)
 {
 	u32 tbd;
+	struct dp_link_private *link;
+
+	link = container_of(dp_link, struct dp_link_private, dp_link);
 
 	/*
 	 * Few simplistic rules and assumptions made here:
@@ -1196,12 +1199,13 @@ u32 dp_link_get_test_bits_depth(struct dp_link *dp_link, u32 bpp)
 		tbd = DP_TEST_BIT_DEPTH_10;
 		break;
 	default:
-		tbd = DP_TEST_BIT_DEPTH_UNKNOWN;
+		drm_dbg_dp(link->drm_dev, "bpp=%d not supported, use bpc=8\n",
+			   bpp);
+		tbd = DP_TEST_BIT_DEPTH_8;
 		break;
 	}
 
-	if (tbd != DP_TEST_BIT_DEPTH_UNKNOWN)
-		tbd = (tbd >> DP_TEST_BIT_DEPTH_SHIFT);
+	tbd = (tbd >> DP_TEST_BIT_DEPTH_SHIFT);
 
 	return tbd;
 }