linux-kernel - Re: [PATCH v4 06/10] drm/msm/dsi: Migrate to drm_dsc_compute_rc

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Date:   Wed, 26 Oct 2022 22:41:53 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Marijn Suijten <marijn.suijten@...ainline.org>,
        phone-devel@...r.kernel.org, Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        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 06/10] drm/msm/dsi: Migrate to
 drm_dsc_compute_rc_parameters()

On 26/10/2022 21:28, Marijn Suijten wrote:
> As per the FIXME this code is entirely duplicate with what is already
> provided inside drm_dsc_compute_rc_parameters(), supposedly because that
> function was yielding "incorrect" results while in reality the panel
> driver(s?) used for testing were providing incorrect parameters.
> 
> For example, this code from downstream assumed dsc->bits_per_pixel to
> contain an integer value, whereas the upstream drm_dsc_config struct
> stores it with 4 fractional bits.  drm_dsc_compute_rc_parameters()
> already accounts for this feat while the panel driver used for testing
> [1] wasn't, hence making drm_dsc_compute_rc_parameters() seem like it
> was returning an incorrect result.
> Other users of dsc->bits_per_pixel inside dsi_populate_dsc_params() also
> treat it in the same erroneous way, and will be addressed in a separate
> patch.
> In the end, using drm_dsc_compute_rc_parameters() spares both a lot of
> duplicate code and erratic behaviour.
> 
> [1]: https://git.linaro.org/people/vinod.koul/kernel.git/commit/?h=topic/pixel3_5.18-rc1&id=1d7d98ad564f1ec69e7525e07418918d90f247a1
> 
> Fixes: b9080324d6ca ("drm/msm/dsi: add support for dsc data")
> Reviewed-by: Abhinav Kumar <quic_abhinavk@...cinc.com>
> Signed-off-by: Marijn Suijten <marijn.suijten@...ainline.org>
> ---
>   drivers/gpu/drm/msm/dsi/dsi_host.c | 64 +++---------------------------
>   1 file changed, 6 insertions(+), 58 deletions(-)

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>

Thank you for the expanded explanation.

-- 
With best wishes
Dmitry