[PATCH v2 5/5] drm/i915/dp: Handle Synaptics DSC throughput link-bpp quirk

[Imre Deak <imre.deak@intel.com>]

Handle the DSC pixel throughput quirk, limiting the compressed link-bpp
value for Synaptics Panamera branch devices, working around a
blank/unstable output issue observed on docking stations containing
these branch devices, when using a mode with a high pixel clock and a
high compressed link-bpp value.

For now use the same mode clock limit for RGB/YUV444 and YUV422/420
output modes. This may result in limiting the link-bpp value for a
YUV422/420 output mode already at a lower than required mode clock.

v2: Apply the quirk only when DSC is enabled.

Reported-by: Vidya Srinivas <vidya.srinivas@intel.com>
Reported-by: Swati Sharma <swati2.sharma@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
---
 .../drm/i915/display/intel_display_types.h    |  1 +
 drivers/gpu/drm/i915/display/intel_dp.c       | 58 +++++++++++++++++++
 2 files changed, 59 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
index 73bdafae604f..aff63bf0f229 100644
--- a/drivers/gpu/drm/i915/display/intel_display_types.h
+++ b/drivers/gpu/drm/i915/display/intel_display_types.h
@@ -551,6 +551,7 @@ struct intel_connector {
 		u8 fec_capability;
 
 		u8 dsc_hblank_expansion_quirk:1;
+		u8 dsc_throughput_quirk:1;
 		u8 dsc_decompression_enabled:1;
 
 		struct {
diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index dd082d2fcc96..5e7aea560910 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -2509,6 +2509,56 @@ int intel_dp_dsc_compute_config(struct intel_dp *intel_dp,
 	return 0;
 }
 
+static void
+adjust_limits_for_dsc_throughput_quirk(const struct intel_connector *connector,
+				       const struct intel_crtc_state *crtc_state,
+				       struct link_config_limits *limits)
+{
+	struct intel_display *display = to_intel_display(connector);
+	const struct intel_crtc *crtc = to_intel_crtc(crtc_state->uapi.crtc);
+	const struct drm_display_mode *adjusted_mode =
+		&crtc_state->hw.adjusted_mode;
+	int max_bpp_x16;
+
+	if (!connector->dp.dsc_throughput_quirk)
+		return;
+
+	/*
+	 * Synaptics Panamera branch devices have a problem decompressing a
+	 * stream with a compressed link-bpp higher than 12, if the pixel
+	 * clock is higher than ~50 % of the maximum overall throughput
+	 * reported by the branch device. Work around this by limiting the
+	 * maximum link bpp for such pixel clocks.
+	 *
+	 * TODO: Use the throughput value specific to the actual RGB/YUV
+	 * format of the output, after determining the pixel clock limit for
+	 * YUV modes. For now use the smaller of the throughput values, which
+	 * may result in limiting the link-bpp value already at a lower than
+	 * required mode clock in case of native YUV422/420 output formats.
+	 * The RGB/YUV444 throughput value should be always either equal or
+	 * smaller than the YUV422/420 value, but let's not depend on this
+	 * assumption.
+	 */
+	if (adjusted_mode->crtc_clock <
+	    min(connector->dp.dsc_branch_caps.overall_throughput.rgb_yuv444,
+		connector->dp.dsc_branch_caps.overall_throughput.yuv422_420) / 2)
+		return;
+
+	max_bpp_x16 = clamp(fxp_q4_from_int(12),
+			    limits->link.min_bpp_x16, limits->link.max_bpp_x16);
+
+	if (max_bpp_x16 >= limits->link.max_bpp_x16)
+		return;
+
+	drm_dbg_kms(display->drm,
+		    "[CRTC:%d:%s][CONNECTOR:%d:%s] Decreasing link max bpp to " FXP_Q4_FMT " due to DSC throughput quirk\n",
+		    crtc->base.base.id, crtc->base.name,
+		    connector->base.base.id, connector->base.name,
+		    FXP_Q4_ARGS(max_bpp_x16));
+
+	limits->link.max_bpp_x16 = max_bpp_x16;
+}
+
 /*
  * Calculate the output link min, max bpp values in limits based on the pipe bpp
  * range, crtc_state and dsc mode. Return true on success.
@@ -2558,6 +2608,9 @@ intel_dp_compute_config_link_bpp_limits(struct intel_dp *intel_dp,
 
 	limits->link.max_bpp_x16 = max_link_bpp_x16;
 
+	if (dsc)
+		adjust_limits_for_dsc_throughput_quirk(connector, crtc_state, limits);
+
 	drm_dbg_kms(display->drm,
 		    "[ENCODER:%d:%s][CRTC:%d:%s] DP link limits: pixel clock %d kHz DSC %s max lanes %d max rate %d max pipe_bpp %d max link_bpp " FXP_Q4_FMT "\n",
 		    encoder->base.base.id, encoder->base.name,
@@ -4272,6 +4325,7 @@ void intel_dp_get_dsc_sink_cap(u8 dpcd_rev,
 	connector->dp.fec_capability = 0;
 
 	memset(&connector->dp.dsc_branch_caps, 0, sizeof(connector->dp.dsc_branch_caps));
+	connector->dp.dsc_throughput_quirk = false;
 
 	if (dpcd_rev < DP_DPCD_REV_14)
 		return;
@@ -4292,6 +4346,10 @@ void intel_dp_get_dsc_sink_cap(u8 dpcd_rev,
 		return;
 
 	init_dsc_overall_throughput_limits(connector, is_branch);
+
+	if (drm_dp_has_quirk(desc, DP_DPCD_QUIRK_DSC_THROUGHPUT_BPP_LIMIT) &&
+	    desc->ident.hw_rev == 0x10)
+		connector->dp.dsc_throughput_quirk = true;
 }
 
 static void intel_edp_get_dsc_sink_cap(u8 edp_dpcd_rev, struct intel_connector *connector)
-- 
2.49.1