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

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Message-ID: <dfa12c8b-ccec-261c-9c83-54536e17c02d@linaro.org>
Date:   Wed, 31 May 2023 02:06:24 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Kuogee Hsieh <quic_khsieh@...cinc.com>,
        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()

On 30/05/2023 19:31, Kuogee Hsieh wrote:
> At current implementation, DSI DSC struct is populated at display setup
> during system bootup. This mechanism works fine with embedded display.
> But will run into problem with plugin/unplug oriented external display,
> such as DP, due to DSC struct will become stale once external display
> unplugged. New DSC struct has to be re populated to reflect newer external
> display which just plugged in. Move retrieving of DSI DSC struct to
> atomic_check() so that same mechanism will work for both embedded display
> and external plugin/unplug oriented display.
> 
> Signed-off-by: Kuogee Hsieh <quic_khsieh@...cinc.com>
> ---
>   drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c | 15 ++++++++++++++-
>   drivers/gpu/drm/msm/msm_drv.h               |  6 ++++++
>   2 files changed, 20 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> index 3b416e1..2927d20 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> @@ -16,6 +16,8 @@
>   #include <drm/drm_crtc.h>
>   #include <drm/drm_file.h>
>   #include <drm/drm_probe_helper.h>
> +#include <drm/drm_bridge.h>
> +#include <drm/drm_fixed.h>
>   
>   #include "msm_drv.h"
>   #include "dpu_kms.h"
> @@ -639,6 +641,15 @@ static int dpu_encoder_virt_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.

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.

> +		}
> +	}
> +
>   	topology = dpu_encoder_get_topology(dpu_enc, dpu_kms, adj_mode, crtc_state);
>   
>   	/*
> @@ -2121,8 +2132,10 @@ void dpu_encoder_helper_phys_cleanup(struct dpu_encoder_phys *phys_enc)
>   					phys_enc->hw_pp->merge_3d->idx);
>   	}
>   
> -	if (dpu_enc->dsc)
> +	if (dpu_enc->dsc) {
>   		dpu_encoder_unprep_dsc(dpu_enc);
> +		dpu_enc->dsc = NULL;
> +	}
>   
>   	intf_cfg.stream_sel = 0; /* Don't care value for video mode */
>   	intf_cfg.mode_3d = dpu_encoder_helper_get_3d_blend_mode(phys_enc);
> diff --git a/drivers/gpu/drm/msm/msm_drv.h b/drivers/gpu/drm/msm/msm_drv.h
> index e13a8cb..5a7c1f4 100644
> --- a/drivers/gpu/drm/msm/msm_drv.h
> +++ b/drivers/gpu/drm/msm/msm_drv.h
> @@ -341,6 +341,7 @@ bool msm_dsi_is_cmd_mode(struct msm_dsi *msm_dsi);
>   bool msm_dsi_is_bonded_dsi(struct msm_dsi *msm_dsi);
>   bool msm_dsi_is_master_dsi(struct msm_dsi *msm_dsi);
>   struct drm_dsc_config *msm_dsi_get_dsc_config(struct msm_dsi *msm_dsi);
> +struct drm_dsc_config *msm_dsi_bridge_get_dsc_config(struct drm_bridge *bridge);
>   #else
>   static inline void __init msm_dsi_register(void)
>   {
> @@ -374,6 +375,11 @@ static inline struct drm_dsc_config *msm_dsi_get_dsc_config(struct msm_dsi *msm_
>   {
>   	return NULL;
>   }
> +
> +struct drm_dsc_config *msm_dsi_bridge_get_dsc_config(struct drm_bridge *bridge)
> +{
> +	return NULL;
> +}

These two chunks belong to the previous patch.

>   #endif
>   
>   #ifdef CONFIG_DRM_MSM_DP

-- 
With best wishes
Dmitry