drm/i915/ddi: start distinguishing 128b/132b SST and MST at state readout

We'll want to distinguish 128b/132b SST and MST modes at state
readout. There's a catch, though. From the hardware perspective,
128b/132b SST and MST programming are pretty much the same. And we can't
really ask the sink at this point.

If we have more than one transcoder in 128b/132b mode associated with
the port, we can safely assume it's MST. But for MST with only a single
stream enabled, we are pretty much out of luck. Let's fall back to
looking at the software state, i.e. intel_dp->is_mst. It should be fine
for the state checker, but for hardware takeover at probe, we'll have to
trust the GOP has only enabled SST.

TODO: Not sure how this *or* our current code handles 128b/132b enabled
by GOP.

Cc: Imre Deak <imre.deak@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/119a773a0d4d74ad204435e462f8d12cb0ea4128.1735912293.git.jani.nikula@intel.com

Author: jnikula

drivers/gpu/drm/i915/display/intel_ddi.c

@@ -787,7 +787,7 @@ static void intel_ddi_get_encoder_pipes(struct intel_encoder *encoder,
 	intel_wakeref_t wakeref;
 	enum pipe p;
 	u32 tmp;
-	u8 mst_pipe_mask;
+	u8 mst_pipe_mask = 0, dp128b132b_pipe_mask = 0;
 
 	*pipe_mask = 0;
 	*is_dp_mst = false;
@@ -824,7 +824,6 @@ static void intel_ddi_get_encoder_pipes(struct intel_encoder *encoder,
 		goto out;
 	}
 
-	mst_pipe_mask = 0;
 	for_each_pipe(dev_priv, p) {
 		enum transcoder cpu_transcoder = (enum transcoder)p;
 		u32 port_mask, ddi_select, ddi_mode;
@@ -853,9 +852,10 @@ static void intel_ddi_get_encoder_pipes(struct intel_encoder *encoder,
 
 		ddi_mode = tmp & TRANS_DDI_MODE_SELECT_MASK;
 
-		if (ddi_mode == TRANS_DDI_MODE_SELECT_DP_MST ||
-		    (ddi_mode == TRANS_DDI_MODE_SELECT_FDI_OR_128B132B && HAS_DP20(display)))
+		if (ddi_mode == TRANS_DDI_MODE_SELECT_DP_MST)
 			mst_pipe_mask |= BIT(p);
+		else if (ddi_mode == TRANS_DDI_MODE_SELECT_FDI_OR_128B132B && HAS_DP20(display))
+			dp128b132b_pipe_mask |= BIT(p);
 
 		*pipe_mask |= BIT(p);
 	}
@@ -865,6 +865,23 @@ static void intel_ddi_get_encoder_pipes(struct intel_encoder *encoder,
 			    "No pipe for [ENCODER:%d:%s] found\n",
 			    encoder->base.base.id, encoder->base.name);
 
+	if (!mst_pipe_mask && dp128b132b_pipe_mask) {
+		struct intel_dp *intel_dp = enc_to_intel_dp(encoder);
+
+		/*
+		 * If we don't have 8b/10b MST, but have more than one
+		 * transcoder in 128b/132b mode, we know it must be 128b/132b
+		 * MST.
+		 *
+		 * Otherwise, we fall back to checking the current MST
+		 * state. It's not accurate for hardware takeover at probe, but
+		 * we don't expect MST to have been enabled at that point, and
+		 * can assume it's SST.
+		 */
+		if (hweight8(dp128b132b_pipe_mask) > 1 || intel_dp->is_mst)
+			mst_pipe_mask = dp128b132b_pipe_mask;
+	}
+
 	if (!mst_pipe_mask && hweight8(*pipe_mask) > 1) {
 		drm_dbg_kms(&dev_priv->drm,
 			    "Multiple pipes for [ENCODER:%d:%s] (pipe_mask %02x)\n",
@@ -875,9 +892,9 @@ static void intel_ddi_get_encoder_pipes(struct intel_encoder *encoder,
 
 	if (mst_pipe_mask && mst_pipe_mask != *pipe_mask)
 		drm_dbg_kms(&dev_priv->drm,
-			    "Conflicting MST and non-MST state for [ENCODER:%d:%s] (pipe_mask %02x mst_pipe_mask %02x)\n",
+			    "Conflicting MST and non-MST state for [ENCODER:%d:%s] (pipe masks: all %02x, MST %02x, 128b/132b %02x)\n",
 			    encoder->base.base.id, encoder->base.name,
-			    *pipe_mask, mst_pipe_mask);
+			    *pipe_mask, mst_pipe_mask, dp128b132b_pipe_mask);
 	else
 		*is_dp_mst = mst_pipe_mask;