linux-kernel - Re: [Freedreno] [RFC PATCH 1/2] drm/msm/dpu: add dsc helper functions

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Message-ID: <CAA8EJpq_mwUt0+1yGYo6hRx8Vz12DumVdpEjJbPk8gGHhGZ2bA@mail.gmail.com>
Date:   Thu, 16 Mar 2023 18:03:33 +0200
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Jessica Zhang <quic_jesszhan@...cinc.com>
Cc:     Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        quic_sbillaka@...cinc.com, sean@...rly.run, andersson@...nel.org,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        dianders@...omium.org, vkoul@...nel.org, agross@...nel.org,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        marijn.suijten@...ainline.org, swboyd@...omium.org,
        Kuogee Hsieh <quic_khsieh@...cinc.com>,
        freedreno@...ts.freedesktop.org,
        Intel Graphics Development <intel-gfx@...ts.freedesktop.org>,
        linux-arm-msm@...r.kernel.org
Subject: Re: [Freedreno] [RFC PATCH 1/2] drm/msm/dpu: add dsc helper functions

Hi,

[removed previous conversation]

>
> Hi Dmitry and Abhinav,
>
> Just wanted to follow up on this thread. I've gone over the MSM-specific
> DSC params for DP and DSI and have found a few shared calculations and
> variables between both DSI and DP paths:
>
> - (as mentioned earlier in the thread) almost all the calculations in
> dpu_dsc_populate_dsc_config() match dsi_populate_dsc_params() [1]. The
> only difference in the math I'm seeing is initial_scale_value.

The value in dsi code is valid for initial_offset = 6144. Please use
the formula from the standard (= sde_dsc_populate_dsc_config) and add
it to drm_dsc_helper.c

If I remember correctly the last remaining item in
dsi_populate_dsc_params() (except mentioned initial_offset) was
line_buf_depth, see [3]. I'm not sure about setting it to bpc+1.
According to the standard it should come from a DSC decoder spec,
which means it should be set by the DSI panel driver or via
drm_dp_dsc_sink_line_buf_depth() in the case of DP output.

> - dsc_extra_pclk_cycle_cnt and dce_bytes_per_line, which were introduced
> in Kuogee's v1 DSC series [2], are used for DSI, DP, and the DPU timing
> engine. dsc_extra_pclk_cycle_cnt is calculated based on pclk_per_line
> (which is calculated differently between DP and DSI), but
> dce_bytes_per_line is calculated the same way between DP and DSI.
>
> To avoid having to duplicate math in 2 different places, I think it
> would help to have these calculations in some msm_dsc_helper.c file. Any
> thoughts on this?

dsc_extra_pclk_cycle_cnt and dce_bytes_per_line are used only in DPU
code, so they can stay in DPU driver.

>
> Thanks,
>
> Jessica Zhang
>
> [1]
> https://elixir.bootlin.com/linux/v6.3-rc2/source/drivers/gpu/drm/msm/dsi/dsi_host.c#L1756
>
> [2] https://patchwork.freedesktop.org/patch/519845/?series=113240&rev=1

[3] https://patchwork.freedesktop.org/patch/525441/?series=114472&rev=2



-- 
With best wishes
Dmitry