[Intel-gfx] [PATCH] drm/i915/dp: revert back to max link rate and lane count on eDP

[Jani Nikula]

Commit 7769db588384 ("drm/i915/dp: optimize eDP 1.4+ link config fast
and narrow") started to optize the eDP 1.4+ link config, both per spec
and as preparation for display stream compression support.

Sadly, we again face panels that flat out fail with parameters they
claim to support. Revert, and go back to the drawing board.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=109959
Fixes: 7769db588384 ("drm/i915/dp: optimize eDP 1.4+ link config fast and narrow")
Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
Cc: Manasi Navare <manasi.d.navare at intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi at intel.com>
Cc: Matt Atwood <matthew.s.atwood at intel.com>
Cc: "Lee, Shawn C" <shawn.c.lee at intel.com>
Cc: Dave Airlie <airlied at gmail.com>
Cc: intel-gfx at lists.freedesktop.org
Cc: <stable at vger.kernel.org> # v5.0+
Signed-off-by: Jani Nikula <jani.nikula at intel.com>
---
 drivers/gpu/drm/i915/intel_dp.c | 67 +++++----------------------------
 1 file changed, 9 insertions(+), 58 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 72c490..fd0f53 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -1856,42 +1856,6 @@ intel_dp_compute_link_config_wide(struct intel_dp *intel_dp,
 	return -EINVAL;
 }
 
-/* Optimize link config in order: max bpp, min lanes, min clock */
-static int
-intel_dp_compute_link_config_fast(struct intel_dp *intel_dp,
-				  struct intel_crtc_state *pipe_config,
-				  const struct link_config_limits *limits)
-{
-	struct drm_display_mode *adjusted_mode = &pipe_config->base.adjusted_mode;
-	int bpp, clock, lane_count;
-	int mode_rate, link_clock, link_avail;
-
-	for (bpp = limits->max_bpp; bpp >= limits->min_bpp; bpp -= 2 * 3) {
-		mode_rate = intel_dp_link_required(adjusted_mode->crtc_clock,
-						   bpp);
-
-		for (lane_count = limits->min_lane_count;
-		     lane_count <= limits->max_lane_count;
-		     lane_count <<= 1) {
-			for (clock = limits->min_clock; clock <= limits->max_clock; clock++) {
-				link_clock = intel_dp->common_rates[clock];
-				link_avail = intel_dp_max_data_rate(link_clock,
-								    lane_count);
-
-				if (mode_rate <= link_avail) {
-					pipe_config->lane_count = lane_count;
-					pipe_config->pipe_bpp = bpp;
-					pipe_config->port_clock = link_clock;
-
-					return 0;
-				}
-			}
-		}
-	}
-
-	return -EINVAL;
-}
-
 static int intel_dp_dsc_compute_bpp(struct intel_dp *intel_dp, u8 dsc_max_bpc)
 {
 	int i, num_bpc;
@@ -2031,12 +1995,10 @@ intel_dp_compute_link_config(struct intel_encoder *encoder,
 	if (intel_dp_is_edp(intel_dp) && intel_dp->edp_dpcd[0] < DP_EDP_14) {
 		/*
 		 * Use the maximum clock and number of lanes the eDP panel
-		 * advertizes being capable of. The eDP 1.3 and earlier panels
-		 * are generally designed to support only a single clock and
-		 * lane configuration, and typically these values correspond to
-		 * the native resolution of the panel. With eDP 1.4 rate select
-		 * and DSC, this is decreasingly the case, and we need to be
-		 * able to select less than maximum link config.
+		 * advertizes being capable of. The panels are generally
+		 * designed to support only a single clock and lane
+		 * configuration, and typically these values correspond to the
+		 * native resolution of the panel.
 		 */
 		limits.min_lane_count = limits.max_lane_count;
 		limits.min_clock = limits.max_clock;
@@ -2050,22 +2012,11 @@ intel_dp_compute_link_config(struct intel_encoder *encoder,
 		      intel_dp->common_rates[limits.max_clock],
 		      limits.max_bpp, adjusted_mode->crtc_clock);
 
-	if (intel_dp_is_edp(intel_dp))
-		/*
-		 * Optimize for fast and narrow. eDP 1.3 section 3.3 and eDP 1.4
-		 * section A.1: "It is recommended that the minimum number of
-		 * lanes be used, using the minimum link rate allowed for that
-		 * lane configuration."
-		 *
-		 * Note that we use the max clock and lane count for eDP 1.3 and
-		 * earlier, and fast vs. wide is irrelevant.
-		 */
-		ret = intel_dp_compute_link_config_fast(intel_dp, pipe_config,
-							&limits);
-	else
-		/* Optimize for slow and wide. */
-		ret = intel_dp_compute_link_config_wide(intel_dp, pipe_config,
-							&limits);
+	/*
+	 * Optimize for slow and wide. This is the place to add alternative
+	 * optimization policy.
+	 */
+	ret = intel_dp_compute_link_config_wide(intel_dp, pipe_config, &limits);
 
 	/* enable compression if the mode doesn't fit available BW */
 	DRM_DEBUG_KMS("Force DSC en = %d\n", intel_dp->force_dsc_en);
-- 
2.20.1