drm/vc4: kms: Don't disable the muxing of an active CRTC

The current HVS muxing code will consider the CRTCs in a given state to
setup their muxing in the HVS, and disable the other CRTCs muxes.

However, it's valid to only update a single CRTC with a state, and in this
situation we would mux out a CRTC that was enabled but left untouched by
the new state.

Fix this by setting a flag on the CRTC state when the muxing has been
changed, and only change the muxing configuration when that flag is there.

Fixes: 87ebcd42 ("drm/vc4: crtc: Assign output to channel automatically")
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Tested-by: Hoegeun Kwon <hoegeun.kwon@samsung.com>
Reviewed-by: Hoegeun Kwon <hoegeun.kwon@samsung.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20201120144245.398711-3-maxime@cerno.tech

drivers/gpu/drm/vc4/vc4_drv.h

@@ -532,6 +532,9 @@ struct vc4_crtc_state {
 		unsigned int top;
 		unsigned int bottom;
 	} margins;
+
+	/* Transitional state below, only valid during atomic commits */
+	bool update_muxing;
 };
 
 #define VC4_HVS_CHANNEL_DISABLED ((unsigned int)-1)

drivers/gpu/drm/vc4/vc4_kms.c

@@ -239,10 +239,7 @@ static void vc5_hvs_pv_muxing_commit(struct vc4_dev *vc4,
 {
 	struct drm_crtc_state *crtc_state;
 	struct drm_crtc *crtc;
-	unsigned char dsp2_mux = 0;
-	unsigned char dsp3_mux = 3;
-	unsigned char dsp4_mux = 3;
-	unsigned char dsp5_mux = 3;
+	unsigned char mux;
 	unsigned int i;
 	u32 reg;
 
@@ -250,50 +247,59 @@ static void vc5_hvs_pv_muxing_commit(struct vc4_dev *vc4,
 		struct vc4_crtc_state *vc4_state = to_vc4_crtc_state(crtc_state);
 		struct vc4_crtc *vc4_crtc = to_vc4_crtc(crtc);
 
-		if (!crtc_state->active)
+		if (!vc4_state->update_muxing)
 			continue;
 
 		switch (vc4_crtc->data->hvs_output) {
 		case 2:
-			dsp2_mux = (vc4_state->assigned_channel == 2) ? 0 : 1;
-			break;
-
-		case 3:
-			dsp3_mux = vc4_state->assigned_channel;
-			break;
-
-		case 4:
-			dsp4_mux = vc4_state->assigned_channel;
-			break;
-
-		case 5:
-			dsp5_mux = vc4_state->assigned_channel;
-			break;
-
-		default:
-			break;
-		}
-	}
-
+			mux = (vc4_state->assigned_channel == 2) ? 0 : 1;
 			reg = HVS_READ(SCALER_DISPECTRL);
 			HVS_WRITE(SCALER_DISPECTRL,
 				  (reg & ~SCALER_DISPECTRL_DSP2_MUX_MASK) |
-		  VC4_SET_FIELD(dsp2_mux, SCALER_DISPECTRL_DSP2_MUX));
+				  VC4_SET_FIELD(mux, SCALER_DISPECTRL_DSP2_MUX));
+			break;
+
+		case 3:
+			if (vc4_state->assigned_channel == VC4_HVS_CHANNEL_DISABLED)
+				mux = 3;
+			else
+				mux = vc4_state->assigned_channel;
 
 			reg = HVS_READ(SCALER_DISPCTRL);
 			HVS_WRITE(SCALER_DISPCTRL,
 				  (reg & ~SCALER_DISPCTRL_DSP3_MUX_MASK) |
-		  VC4_SET_FIELD(dsp3_mux, SCALER_DISPCTRL_DSP3_MUX));
+				  VC4_SET_FIELD(mux, SCALER_DISPCTRL_DSP3_MUX));
+			break;
+
+		case 4:
+			if (vc4_state->assigned_channel == VC4_HVS_CHANNEL_DISABLED)
+				mux = 3;
+			else
+				mux = vc4_state->assigned_channel;
 
 			reg = HVS_READ(SCALER_DISPEOLN);
 			HVS_WRITE(SCALER_DISPEOLN,
 				  (reg & ~SCALER_DISPEOLN_DSP4_MUX_MASK) |
-		  VC4_SET_FIELD(dsp4_mux, SCALER_DISPEOLN_DSP4_MUX));
+				  VC4_SET_FIELD(mux, SCALER_DISPEOLN_DSP4_MUX));
+
+			break;
+
+		case 5:
+			if (vc4_state->assigned_channel == VC4_HVS_CHANNEL_DISABLED)
+				mux = 3;
+			else
+				mux = vc4_state->assigned_channel;
 
 			reg = HVS_READ(SCALER_DISPDITHER);
 			HVS_WRITE(SCALER_DISPDITHER,
 				  (reg & ~SCALER_DISPDITHER_DSP5_MUX_MASK) |
-		  VC4_SET_FIELD(dsp5_mux, SCALER_DISPDITHER_DSP5_MUX));
+				  VC4_SET_FIELD(mux, SCALER_DISPDITHER_DSP5_MUX));
+			break;
+
+		default:
+			break;
+		}
+	}
 }
 
 static void
@@ -789,16 +795,19 @@ static int vc4_pv_muxing_atomic_check(struct drm_device *dev,
 		struct vc4_crtc *vc4_crtc = to_vc4_crtc(crtc);
 		unsigned int matching_channels;
 
-		if (old_crtc_state->enable && !new_crtc_state->enable) {
-			hvs_new_state->unassigned_channels |= BIT(old_vc4_crtc_state->assigned_channel);
-			new_vc4_crtc_state->assigned_channel = VC4_HVS_CHANNEL_DISABLED;
-		}
-
-		if (!new_crtc_state->enable)
+		/* Nothing to do here, let's skip it */
+		if (old_crtc_state->enable == new_crtc_state->enable)
 			continue;
 
-		if (new_vc4_crtc_state->assigned_channel != VC4_HVS_CHANNEL_DISABLED)
+		/* Muxing will need to be modified, mark it as such */
+		new_vc4_crtc_state->update_muxing = true;
+
+		/* If we're disabling our CRTC, we put back our channel */
+		if (!new_crtc_state->enable) {
+			hvs_new_state->unassigned_channels |= BIT(old_vc4_crtc_state->assigned_channel);
+			new_vc4_crtc_state->assigned_channel = VC4_HVS_CHANNEL_DISABLED;
 			continue;
+		}
 
 		/*
 		 * The problem we have to solve here is that we have