linux-kernel - Re: [PATCH v4 00/10] drm/msm: Fix math issues in MSM DSC implementation

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Date:   Fri, 28 Oct 2022 11:33:21 -0700
From:   Abhinav Kumar <quic_abhinavk@...cinc.com>
To:     Marijn Suijten <marijn.suijten@...ainline.org>,
        <phone-devel@...r.kernel.org>, Rob Clark <robdclark@...il.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Vinod Koul <vkoul@...nel.org>
CC:     <~postmarketos/upstreaming@...ts.sr.ht>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...ainline.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Martin Botka <martin.botka@...ainline.org>,
        Jami Kettunen <jami.kettunen@...ainline.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Douglas Anderson <dianders@...omium.org>,
        Vladimir Lypak <vladimir.lypak@...il.com>,
        <linux-arm-msm@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        <freedreno@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 00/10] drm/msm: Fix math issues in MSM DSC
 implementation

Hi Marijn

On 10/26/2022 11:28 AM, Marijn Suijten wrote:
> Various removals of complex yet unnecessary math, fixing all uses of
> drm_dsc_config::bits_per_pixel to deal with the fact that this field
> includes four fractional bits, and finally making sure that
> range_bpg_offset contains values 6-bits wide to prevent overflows in
> drm_dsc_pps_payload_pack().
> 
> Altogether this series is responsible for solving _all_ Display Stream
> Compression issues and artifacts on the Sony Tama (sdm845) Akatsuki
> smartphone (2880x1440p).
> 
> Changes since v3:
> - Swap patch 7 and 8 to make sure msm_host is available inside
>    dsi_populate_dsc_params();
> - Reword patch 6 (Migrate to drm_dsc_compute_rc_parameters()) to more
>    clearly explain why the FIXME wasn't solved initially, but why it can
>    (and should!) be resolved now.
> 
> v3: https://lore.kernel.org/linux-arm-msm/20221009184824.457416-1-marijn.suijten@somainline.org/T/#u
> 
> Changes since v2:
> - Generalize mux_word_size setting depending on bits_per_component;
> - Migrate DSI's DSC calculations to drm_dsc_compute_rc_parameters(),
>    implicitly addressing existing math issues;
> - Disallow any bits_per_component other than 8, until hardcoded values
>    are updated and tested to support such cases.
> 
> v2: https://lore.kernel.org/linux-arm-msm/20221005181657.784375-1-marijn.suijten@somainline.org/T/#u
> 
> Changes since v1:
> 
> - Propagate r-b's, except (obviously) in patches that were (heavily)
>    modified;
> - Remove accidental debug code in dsi_cmd_dma_add;
> - Move Range BPG Offset masking out of DCS PPS packing, back into the
>    DSI driver when it is assigned to drm_dsc_config (this series is now
>    strictly focusing on drm/msm again);
> - Replace modulo-check resulting in conditional increment with
>    DIV_ROUND_UP;
> - Remove repeated calculation of slice_chunk_size;
> - Use u16 instead of int when handling bits_per_pixel;
> - Use DRM_DEV_ERROR instead of pr_err in DSI code;
> - Also remove redundant target_bpp_x16 variable.
> 
> v1: https://lore.kernel.org/linux-arm-msm/20221001190807.358691-1-marijn.suijten@somainline.org/T/#u
> 
> Marijn Suijten (10):
>    drm/msm/dsi: Remove useless math in DSC calculations
>    drm/msm/dsi: Remove repeated calculation of slice_per_intf
>    drm/msm/dsi: Use DIV_ROUND_UP instead of conditional increment on
>      modulo
>    drm/msm/dsi: Reuse earlier computed dsc->slice_chunk_size
>    drm/msm/dsi: Appropriately set dsc->mux_word_size based on bpc
>    drm/msm/dsi: Migrate to drm_dsc_compute_rc_parameters()
>    drm/msm/dsi: Account for DSC's bits_per_pixel having 4 fractional bits
>    drm/msm/dsi: Disallow 8 BPC DSC configuration for alternative BPC
>      values
>    drm/msm/dpu1: Account for DSC's bits_per_pixel having 4 fractional
>      bits
>    drm/msm/dsi: Prevent signed BPG offsets from bleeding into adjacent
>      bits
> 
>   drivers/gpu/drm/msm/disp/dpu1/dpu_hw_dsc.c |  11 +-
>   drivers/gpu/drm/msm/dsi/dsi_host.c         | 121 ++++++---------------
>   2 files changed, 37 insertions(+), 95 deletions(-)
> 
> --
> 2.38.1
> 

To keep the -fixes cycle to have only critical fixes (others are 
important too but are cleanups), I was thinking of absorbing patches 
7,8,9 and 10 alone in the -fixes cycle and for patches 1-6, will go 
through the 6.2 push.

Let me know if there are any concerns if we just take patches 7,8,9 and 
10 separately.

Thanks

Abhinav