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

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Message-ID: <bcbda796-908a-43d5-0744-c03656fda47b@linaro.org>
Date:   Thu, 20 Apr 2023 12:53:58 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Arnaud Vrac <avrac@...ebox.fr>
Cc:     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>, 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 20/04/2023 10:26, Arnaud Vrac wrote:
> Le jeu. 20 avr. 2023 à 00:43, Dmitry Baryshkov
> <dmitry.baryshkov@...aro.org> a écrit :
>>
>> 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().
> 
> Ok, I did test with 2 LMs and it seems to be working, I'll investigate.

The only reference I have here is the fbdev driver, see [1]. The newer 
SDE driver doesn't handle STAGE_BASE vs STAGE0 (and DPU inherited that 
design). Maybe this got fixed in hw at some point.

[1] 
https://git.codelinaro.org/clo/la/kernel/msm-4.19/-/blob/LE.UM.4.4.1.r2-17500-QRB5165.0/drivers/video/fbdev/msm/mdss_mdp_pipe.c#L1789

I think, it only concerns the src_split + multirect cases, where the 
rectangle base point is on the right LM.

> 
>>
>> 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.
> 
> I also tested with both fullscreen and non-fullscreen primary plane,
> and no plane. I'll check this.

Yes, the DPU driver always enables the MIXER_BORDER_OUT.

> 
>>
>>> ---
>>>    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
>>

-- 
With best wishes
Dmitry