linux-kernel - Re: [PATCH v1 2/3] drm/msm/dpu: retrieve DSI DSC struct at atomic

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Date:   Wed, 31 May 2023 08:40:26 -0700
From:   Kuogee Hsieh <quic_khsieh@...cinc.com>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        <dri-devel@...ts.freedesktop.org>, <robdclark@...il.com>,
        <sean@...rly.run>, <swboyd@...omium.org>, <dianders@...omium.org>,
        <vkoul@...nel.org>, <daniel@...ll.ch>, <airlied@...il.com>,
        <agross@...nel.org>, <andersson@...nel.org>
CC:     <quic_abhinavk@...cinc.com>, <quic_jesszhan@...cinc.com>,
        <quic_sbillaka@...cinc.com>, <marijn.suijten@...ainline.org>,
        <freedreno@...ts.freedesktop.org>, <linux-arm-msm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 2/3] drm/msm/dpu: retrieve DSI DSC struct at
 atomic_check()



>>   +    if (dpu_enc->disp_info.intf_type == DRM_MODE_ENCODER_DSI) {
>
> INTF_DSI
>
>> +        struct drm_bridge *bridge;
>> +
>> +        if (!dpu_enc->dsc) {
>
> This condition is not correct. We should be updating the DSC even if 
> there is one.
>
>> +            bridge = drm_bridge_chain_get_first_bridge(drm_enc);
>> +            dpu_enc->dsc = msm_dsi_bridge_get_dsc_config(bridge);
>
> This approach will not work for the hot-pluggable outputs. The dpu_enc 
> is not a part of the state. It should not be touched before 
> atomic_commit actually commits changes.
where can drm_dsc_config be stored?
>
> Also, I don't think I like the API. It makes it impossible for the 
> driver to check that the bridge is the actually our DSI bridge or not.
> Once you add DP here, the code will explode.
>
> I think instead we should extend the drm_bridge API to be able to get 
> the DSC configuration from it directly. Additional care should be put 
> to design an assymetrical API. Theoretically a drm_bridge can be both 
> DSC source and DSC sink. Imagine a DSI-to-DP or DSI-to-HDMI bridge, 
> supporting DSC on the DSI side too.

Form my understanding, a bridge contains two interfaces.

Therefore I would think only one bridge for dsi-to-dp bridge? and this 
bridge should represent the bridge chip?

I am thinking adding an ops function, get_bridge_dsc() to struct 
drm_bridge_funcs to retrieve drm_dsc_config.

Do you have other suggestion?

>