linux-kernel - Re: [PATCH v3 08/10] drm/msm/dsi: Account for DSC's bits_per

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Message-ID: <13755211-82fe-937b-f96e-966a55e68917@linaro.org>
Date:   Sun, 9 Oct 2022 22:24:36 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Marijn Suijten <marijn.suijten@...ainline.org>,
        phone-devel@...r.kernel.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>,
        Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>, Vinod Koul <vkoul@...nel.org>,
        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 v3 08/10] drm/msm/dsi: Account for DSC's bits_per_pixel
 having 4 fractional bits

On 09/10/2022 21:53, Marijn Suijten wrote:
> drm_dsc_config's bits_per_pixel field holds a fractional value with 4
> bits, which all panel drivers should adhere to for
> drm_dsc_pps_payload_pack() to generate a valid payload.  All code in the
> DSI driver here seems to assume that this field doesn't contain any
> fractional bits, hence resulting in the wrong values being computed.
> Since none of the calculations leave any room for fractional bits or
> seem to indicate any possible area of support, disallow such values
> altogether.  calculate_rc_params() in intel_vdsc.c performs an identical
> bitshift to get at this integer value.
> 
> Fixes: b9080324d6ca ("drm/msm/dsi: add support for dsc data")
> Signed-off-by: Marijn Suijten <marijn.suijten@...ainline.org>

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

> ---
>   drivers/gpu/drm/msm/dsi/dsi_host.c | 19 ++++++++++++++-----
>   1 file changed, 14 insertions(+), 5 deletions(-)
> 

-- 
With best wishes
Dmitry