[PATCH] drm/i915/display/dp: Fix DSC vs lower bpp priority

[Charlton Lin]

Previously driver would lower bpp before trying DSC. Monitors
capable of acheiving highest mode with either DSC or lower bpp
would have bpp dropped instead of attempting DSC at higher bpp.

Changed the order in which driver attempts DSC and lower bpp.
Attempt DSC before trying lower bpp without DSC.

Cc: Ankit Nautiyal <ankit.k.nautiyal at intel.com>
Cc: Suraj Kandpal <suraj.kandpal at intel.com>
Cc: Khaled Almahallawy <khaled.almahallawy at intel.com>
Signed-off-by: Charlton Lin <charlton.lin at intel.com>
---
 drivers/gpu/drm/i915/display/intel_dp.c | 19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index 2206b45bc78c..98231fc7e6e1 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -1527,12 +1527,14 @@ static int
 intel_dp_compute_link_config_wide(struct intel_dp *intel_dp,
 				  struct intel_crtc_state *pipe_config,
 				  const struct drm_connector_state *conn_state,
-				  const struct link_config_limits *limits)
+				  const struct link_config_limits *limits,
+				  bool allow_bpp_change)
 {
 	int bpp, i, lane_count, clock = intel_dp_mode_clock(pipe_config, conn_state);
 	int mode_rate, link_rate, link_avail;
+	int min_bpp = allow_bpp_change ? limits->min_bpp : limits->max_bpp;
 
-	for (bpp = limits->max_bpp; bpp >= limits->min_bpp; bpp -= 2 * 3) {
+	for (bpp = limits->max_bpp; bpp >= min_bpp; bpp -= 2 * 3) {
 		int link_bpp = intel_dp_output_bpp(pipe_config->output_format, bpp);
 
 		mode_rate = intel_dp_link_required(clock, link_bpp);
@@ -2247,7 +2249,8 @@ intel_dp_compute_link_config(struct intel_encoder *encoder,
 	 * Optimize for slow and wide for everything, because there are some
 	 * eDP 1.3 and 1.4 panels don't work well with fast and narrow.
 	 */
-	ret = intel_dp_compute_link_config_wide(intel_dp, pipe_config, conn_state, &limits);
+	ret = intel_dp_compute_link_config_wide(intel_dp, pipe_config,
+				m		conn_state, &limits, false);
 
 	if (ret || joiner_needs_dsc || intel_dp->force_dsc_en) {
 		drm_dbg_kms(&i915->drm, "Try DSC (fallback=%s, joiner=%s, force=%s)\n",
@@ -2255,10 +2258,16 @@ intel_dp_compute_link_config(struct intel_encoder *encoder,
 			    str_yes_no(intel_dp->force_dsc_en));
 		ret = intel_dp_dsc_compute_config(intel_dp, pipe_config,
 						  conn_state, &limits, 64, true);
-		if (ret < 0)
-			return ret;
 	}
 
+	if (ret < 0)
+		ret = intel_dp_compute_link_config_wide(intel_dp, pipe_config,
+							conn_state, &limits,
+							true);
+
+	if (ret < 0)
+		return ret;
+
 	if (pipe_config->dsc.compression_enable) {
 		drm_dbg_kms(&i915->drm,
 			    "DP lane count %d clock %d Input bpp %d Compressed bpp %d\n",
-- 
2.25.1