drm/i915/dp: Handle Synaptics DSC throughput link-bpp quirk

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.
v3 (Ville):
- Move adjustment of link-bpp within the already existing is_dsc
  if branch.
- Add TODO comment to move the HW revision check as well to the
  DRM core quirk table.
v4:
- Fix incorrect fxp_q4_from_int(INT_MAX) vs. INT_MAX return value
  from dsc_throughput_quirk_max_bpp_x16().

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reported-by: Vidya Srinivas <vidya.srinivas@intel.com>
Reported-and-tested-by: Swati Sharma <swati2.sharma@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://lore.kernel.org/r/20250930182450.563016-7-imre.deak@intel.com

2 files changed, 58 insertions, 0 deletions

diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
index 99d2c3123692..ca5a87772e93 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 9de9356302f9..8a2fc1fcb5d0 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -2485,6 +2485,40 @@ int intel_dp_dsc_compute_config(struct intel_dp *intel_dp,
 	return 0;
 }
 
+static int
+dsc_throughput_quirk_max_bpp_x16(const struct intel_connector *connector,
+				 const struct intel_crtc_state *crtc_state)
+{
+	const struct drm_display_mode *adjusted_mode =
+		&crtc_state->hw.adjusted_mode;
+
+	if (!connector->dp.dsc_throughput_quirk)
+		return INT_MAX;
+
+	/*
+	 * 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 INT_MAX;
+
+	return fxp_q4_from_int(12);
+}
+
 /*
  * 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.
@@ -2516,6 +2550,7 @@ intel_dp_compute_config_link_bpp_limits(struct intel_dp *intel_dp,
 	} else {
 		int dsc_src_min_bpp, dsc_sink_min_bpp, dsc_min_bpp;
 		int dsc_src_max_bpp, dsc_sink_max_bpp, dsc_max_bpp;
+		int throughput_max_bpp_x16;
 
 		dsc_src_min_bpp = intel_dp_dsc_min_src_compressed_bpp();
 		dsc_sink_min_bpp = intel_dp_dsc_sink_min_compressed_bpp(crtc_state);
@@ -2530,6 +2565,19 @@ intel_dp_compute_config_link_bpp_limits(struct intel_dp *intel_dp,
 			      min(dsc_sink_max_bpp, dsc_src_max_bpp) : dsc_src_max_bpp;
 
 		max_link_bpp_x16 = min(max_link_bpp_x16, fxp_q4_from_int(dsc_max_bpp));
+
+		throughput_max_bpp_x16 = dsc_throughput_quirk_max_bpp_x16(connector, crtc_state);
+		throughput_max_bpp_x16 = clamp(throughput_max_bpp_x16,
+					       limits->link.min_bpp_x16, max_link_bpp_x16);
+		if (throughput_max_bpp_x16 < max_link_bpp_x16) {
+			max_link_bpp_x16 = throughput_max_bpp_x16;
+
+			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_link_bpp_x16));
+		}
 	}
 
 	limits->link.max_bpp_x16 = max_link_bpp_x16;
@@ -4237,6 +4285,7 @@ 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;
@@ -4257,6 +4306,14 @@ void intel_dp_get_dsc_sink_cap(u8 dpcd_rev,
 		return;
 
 	init_dsc_overall_throughput_limits(connector, is_branch);
+
+	/*
+	 * TODO: Move the HW rev check as well to the DRM core quirk table if
+	 * that's required after clarifying the list of affected devices.
+	 */
+	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)