linux-kernel - Re: [PATCH 0/3] Add support for databus widen mode

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Message-ID: <8d5870f8-e530-fa8f-444a-3d3ccf716d48@linaro.org>
Date:   Fri, 16 Jun 2023 14:30:20 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Jessica Zhang <quic_jesszhan@...cinc.com>,
        Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Marijn Suijten <marijn.suijten@...ainline.org>
Cc:     quic_abhinavk@...cinc.com, linux-arm-msm@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] Add support for databus widen mode

On 14/06/2023 04:57, Jessica Zhang wrote:
> DPU 5.x+ and DSI 6G 2.5.x+ support a databus-widen mode that allows for
> more compressed data to be transferred per pclk.
> 
> This series adds support for enabling this feature for both DPU and DSI
> by doing the following:
> 
> 1. Add a DPU_INTF_DATABUS_WIDEN feature flag
> 2. Add a DPU INTF op to set the DATABUS_WIDEN register
> 3. Set the DATABUS_WIDEN register and do the proper hdisplay
>     calculations in DSI when applicable

As I was writing the documentation patch, another thought stroke me wrt 
this patchset. Could you please add a check to DSI's mode_valid 
disallowing all modes if DSI_BPP > 8 & !widebus. Technically this check 
does not filter modes per se, but in my opinion ending up with empty 
modes list would be a better user experience compared to having a list 
of modes, from which none can be selected.

And if we ever get dynamic mode/dsc_config setup, this would allow us to 
filter unsupported modes via their DSC confiuration.

Abhinav, I remember, that you told me that adding drm_dsc_config to drm 
modes was forbidden already. However this looks like a valid reason to 
maybe restart the discussion: we want to filter modes basing on the 
corresponding DSC data rather than allowing the mode in mode_valid() and 
then failing it in the atomic_check().

> 
> Note: This series will only enable the databus-widen mode for command
> mode as we are currently unable to validate it on video mode.
> 
> Depends on: "Add DSC v1.2 Support for DSI" [1]
> 
> [1] https://patchwork.freedesktop.org/series/117219/
> 
> Signed-off-by: Jessica Zhang <quic_jesszhan@...cinc.com>

Nit: there is no need to sign-off the cover letters.

> ---
> Jessica Zhang (3):
>        drm/msm/dpu: Add DPU_INTF_DATABUS_WIDEN feature flag for DPU >= 5.0
>        drm/msm/dpu: Set DATABUS_WIDEN on command mode encoders
>        drm/msm/dsi: Enable DATABUS_WIDEN for DSI command mode
> 
>   drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_cmd.c |  3 +++
>   drivers/gpu/drm/msm/disp/dpu1/dpu_hw_catalog.c       |  3 ++-
>   drivers/gpu/drm/msm/disp/dpu1/dpu_hw_catalog.h       |  2 ++
>   drivers/gpu/drm/msm/disp/dpu1/dpu_hw_intf.c          | 12 ++++++++++++
>   drivers/gpu/drm/msm/disp/dpu1/dpu_hw_intf.h          |  3 +++
>   drivers/gpu/drm/msm/dsi/dsi.xml.h                    |  1 +
>   drivers/gpu/drm/msm/dsi/dsi_host.c                   | 19 ++++++++++++++++++-
>   7 files changed, 41 insertions(+), 2 deletions(-)
> ---
> base-commit: 1981c2c0c05f5d7fe4d4552d4f352cb46840e51e
> change-id: 20230525-add-widebus-support-f785546ee751
> 
> Best regards,

-- 
With best wishes
Dmitry