linux-kernel - Re: [PATCH 04/11] drm/msm/dpu: allow using lm mixer base stage

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Date:   Thu, 20 Apr 2023 01:43:04 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Arnaud Vrac <avrac@...ebox.fr>, Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 04/11] drm/msm/dpu: allow using lm mixer base stage

On 19/04/2023 17:41, Arnaud Vrac wrote:
> The dpu backend already handles applying alpha to the base stage, so we
> can use it to render the bottom plane in all cases. This allows mixing
> one additional plane with the hardware mixer.
> 
> Signed-off-by: Arnaud Vrac <avrac@...ebox.fr>

This might require additional changes. First, for the STAGE_BASE pipe 
in the source split mode (iow using two LMs) should programmed with 
respect to the right LM's x offset (rather than usual left top-left LM). 
See  mdss_mdp_pipe_position_update().

Also this might need some interaction with CTL_MIXER_BORDER_OUT being 
set or not. If I remember correctly, if there bottom plane is not 
fullscreen or if there are no planes at all, we should set 
CTL_MIXER_BORDER_OUT (which takes STAGE_BASE) and start assigning them 
from STAGE0. If not, we can use STAGE_BASE.

> ---
>   drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c
> index 14b5cfe306113..148921ed62f85 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_plane.c
> @@ -881,7 +881,7 @@ static int dpu_plane_atomic_check(struct drm_plane *plane,
>   	r_pipe->multirect_mode = DPU_SSPP_MULTIRECT_NONE;
>   	r_pipe->sspp = NULL;
>   
> -	pstate->stage = DPU_STAGE_0 + pstate->base.normalized_zpos;
> +	pstate->stage = DPU_STAGE_BASE + pstate->base.normalized_zpos;
>   	if (pstate->stage >= pdpu->catalog->caps->max_mixer_blendstages) {
>   		DPU_ERROR("> %d plane stages assigned\n",
>   			  pdpu->catalog->caps->max_mixer_blendstages - DPU_STAGE_0);
> 

-- 
With best wishes
Dmitry