drm/msm/dpu: Fall back to a single DSC encoder (1:1:1) on small SoCs

Some SoCs such as SC7280 (used in the Fairphone 5) have only a single
DSC "hard slice" encoder.  The current hardcoded use of 2:2:1 topology
(2 LM and 2 DSC for a single interface) make it impossible to use
Display Stream Compression panels with mainline, which is exactly what's
installed on the Fairphone 5.

By loosening the hardcoded `num_dsc = 2` to fall back to `num_dsc =
1` when the catalog only contains one entry, we can trivially support
this phone and unblock further panel enablement on mainline.  A few
more supporting changes in this patch ensure hardcoded constants of 2
DSC encoders are replaced to count or read back the actual number of
DSC hardware blocks that are enabled for the given virtual encoder.
Likewise DSC_MODE_SPLIT_PANEL can no longer be unconditionally enabled.

Cc: Luca Weiss <luca.weiss@fairphone.com>
Signed-off-by: Marijn Suijten <marijn.suijten@somainline.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Tested-by: Luca Weiss <luca.weiss@fairphone.com>
Reviewed-by: Jessica Zhang <quic_jesszhan@quicinc.com>
Tested-by: Danila Tikhonov <danila@jiaxyga.com>
Patchwork: https://patchwork.freedesktop.org/patch/633318/
Link: https://lore.kernel.org/r/20250122-dpu-111-topology-v2-1-505e95964af9@somainline.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c

@@ -622,9 +622,9 @@ bool dpu_encoder_use_dsc_merge(struct drm_encoder *drm_enc)
 		if (dpu_enc->phys_encs[i])
 			intf_count++;
 
-	/* See dpu_encoder_get_topology, we only support 2:2:1 topology */
-	if (dpu_enc->dsc)
-		num_dsc = 2;
+	for (i = 0; i < MAX_CHANNELS_PER_ENC; i++)
+		if (dpu_enc->hw_dsc[i])
+			num_dsc++;
 
 	return (num_dsc > 0) && (num_dsc > intf_count);
 }
@@ -686,13 +686,19 @@ static struct msm_display_topology dpu_encoder_get_topology(
 
 	if (dsc) {
 		/*
-		 * In case of Display Stream Compression (DSC), we would use
-		 * 2 DSC encoders, 2 layer mixers and 1 interface
-		 * this is power optimal and can drive up to (including) 4k
-		 * screens
+		 * Use 2 DSC encoders and 2 layer mixers per single interface
+		 * when Display Stream Compression (DSC) is enabled,
+		 * and when enough DSC blocks are available.
+		 * This is power-optimal and can drive up to (including) 4k
+		 * screens.
 		 */
-		topology.num_dsc = 2;
-		topology.num_lm = 2;
+		if (dpu_kms->catalog->dsc_count >= 2) {
+			topology.num_dsc = 2;
+			topology.num_lm = 2;
+		} else {
+			topology.num_dsc = 1;
+			topology.num_lm = 1;
+		}
 		topology.num_intf = 1;
 	}
 
@@ -2020,7 +2026,6 @@ static void dpu_encoder_dsc_pipe_cfg(struct dpu_hw_ctl *ctl,
 static void dpu_encoder_prep_dsc(struct dpu_encoder_virt *dpu_enc,
 				 struct drm_dsc_config *dsc)
 {
-	/* coding only for 2LM, 2enc, 1 dsc config */
 	struct dpu_encoder_phys *enc_master = dpu_enc->cur_master;
 	struct dpu_hw_ctl *ctl = enc_master->hw_ctl;
 	struct dpu_hw_dsc *hw_dsc[MAX_CHANNELS_PER_ENC];
@@ -2030,22 +2035,24 @@ static void dpu_encoder_prep_dsc(struct dpu_encoder_virt *dpu_enc,
 	int dsc_common_mode;
 	int pic_width;
 	u32 initial_lines;
+	int num_dsc = 0;
 	int i;
 
 	for (i = 0; i < MAX_CHANNELS_PER_ENC; i++) {
 		hw_pp[i] = dpu_enc->hw_pp[i];
 		hw_dsc[i] = dpu_enc->hw_dsc[i];
 
-		if (!hw_pp[i] || !hw_dsc[i]) {
-			DPU_ERROR_ENC(dpu_enc, "invalid params for DSC\n");
-			return;
-		}
+		if (!hw_pp[i] || !hw_dsc[i])
+			break;
+
+		num_dsc++;
 	}
 
-	dsc_common_mode = 0;
 	pic_width = dsc->pic_width;
 
-	dsc_common_mode = DSC_MODE_SPLIT_PANEL;
+	dsc_common_mode = 0;
+	if (num_dsc > 1)
+		dsc_common_mode |= DSC_MODE_SPLIT_PANEL;
 	if (dpu_encoder_use_dsc_merge(enc_master->parent))
 		dsc_common_mode |= DSC_MODE_MULTIPLEX;
 	if (enc_master->intf_mode == INTF_MODE_VIDEO)
@@ -2054,14 +2061,10 @@ static void dpu_encoder_prep_dsc(struct dpu_encoder_virt *dpu_enc,
 	this_frame_slices = pic_width / dsc->slice_width;
 	intf_ip_w = this_frame_slices * dsc->slice_width;
 
-	/*
-	 * dsc merge case: when using 2 encoders for the same stream,
-	 * no. of slices need to be same on both the encoders.
-	 */
-	enc_ip_w = intf_ip_w / 2;
+	enc_ip_w = intf_ip_w / num_dsc;
 	initial_lines = dpu_encoder_dsc_initial_line_calc(dsc, enc_ip_w);
 
-	for (i = 0; i < MAX_CHANNELS_PER_ENC; i++)
+	for (i = 0; i < num_dsc; i++)
 		dpu_encoder_dsc_pipe_cfg(ctl, hw_dsc[i], hw_pp[i],
 					 dsc, dsc_common_mode, initial_lines);
 }