When DSC is enabled the number of interfaces is forced to be 1, and
documented that it is a "power-optimal" layout to use two DSC encoders
together with two Layer Mixers.  However, the same layout (two DSC
hard-slice encoders with two LMs) is also used when the display is
fed with data over two instead of one interface (common on 4k@120Hz
smartphone panels with Dual-DSI).  Solve this by simply removing the
num_intf = 1 assignment as the count is already calculated by computing
the number of physical encoders within the virtual encoder.

Fixes: 7e9cc175b159 ("drm/msm/disp/dpu1: Add support for DSC in topology")
Signed-off-by: Marijn Suijten <marijn.suijten@somainline.org>
---
 drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
index b585cd17462345f94bcc2ddd57902cc7c312ae63..b0870318471bd7cceda70fd15ea7bcc8658af604 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
@@ -686,20 +686,21 @@ static struct msm_display_topology dpu_encoder_get_topology(
 
 	if (dsc) {
 		/*
-		 * Use 2 DSC encoders and 2 layer mixers per single interface
+		 * Use 2 DSC encoders, 2 layer mixers and 1 or 2 interfaces
 		 * 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.
 		 */
-		if (dpu_kms->catalog->dsc_count >= 2) {
+		WARN(topology.num_intf > 2,
+		     "DSC topology cannot support more than 2 interfaces\n");
+		if (intf_count >= 2 || 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;
 	}
 
 	return topology;

-- 
2.48.1

On 2/9/2025 1:42 PM, Marijn Suijten wrote:
> When DSC is enabled the number of interfaces is forced to be 1, and
> documented that it is a "power-optimal" layout to use two DSC encoders
> together with two Layer Mixers.  However, the same layout (two DSC
> hard-slice encoders with two LMs) is also used when the display is
> fed with data over two instead of one interface (common on 4k@120Hz
> smartphone panels with Dual-DSI).  Solve this by simply removing the
> num_intf = 1 assignment as the count is already calculated by computing
> the number of physical encoders within the virtual encoder.
> 
> Fixes: 7e9cc175b159 ("drm/msm/disp/dpu1: Add support for DSC in topology")
> Signed-off-by: Marijn Suijten <marijn.suijten@somainline.org>

Reviewed-by: Jessica Zhang <quic_jesszhan@quicinc.com>

> ---
>   drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c | 7 ++++---
>   1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> index b585cd17462345f94bcc2ddd57902cc7c312ae63..b0870318471bd7cceda70fd15ea7bcc8658af604 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> @@ -686,20 +686,21 @@ static struct msm_display_topology dpu_encoder_get_topology(
>   
>   	if (dsc) {
>   		/*
> -		 * Use 2 DSC encoders and 2 layer mixers per single interface
> +		 * Use 2 DSC encoders, 2 layer mixers and 1 or 2 interfaces
>   		 * 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.
>   		 */
> -		if (dpu_kms->catalog->dsc_count >= 2) {
> +		WARN(topology.num_intf > 2,
> +		     "DSC topology cannot support more than 2 interfaces\n");
> +		if (intf_count >= 2 || 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;
>   	}
>   
>   	return topology;
> 
> -- 
> 2.48.1
>

On Sun, Feb 09, 2025 at 10:42:54PM +0100, Marijn Suijten wrote:
> When DSC is enabled the number of interfaces is forced to be 1, and
> documented that it is a "power-optimal" layout to use two DSC encoders
> together with two Layer Mixers.  However, the same layout (two DSC
> hard-slice encoders with two LMs) is also used when the display is
> fed with data over two instead of one interface (common on 4k@120Hz
> smartphone panels with Dual-DSI).  Solve this by simply removing the
> num_intf = 1 assignment as the count is already calculated by computing
> the number of physical encoders within the virtual encoder.
> 
> Fixes: 7e9cc175b159 ("drm/msm/disp/dpu1: Add support for DSC in topology")
> Signed-off-by: Marijn Suijten <marijn.suijten@somainline.org>
> ---
>  drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

-- 
With best wishes
Dmitry