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Message-ID: <CAA8EJpoEUuJqj4hAa-qU1ovZuR0ivu3Jzeyx50JPw3k2mv2Lmg@mail.gmail.com>
Date: Tue, 4 Oct 2022 17:35:46 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Marijn Suijten <marijn.suijten@...ainline.org>
Cc: phone-devel@...r.kernel.org, Rob Clark <robdclark@...il.com>,
Vinod Koul <vkoul@...nel.org>,
~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>,
David Airlie <airlied@...ux.ie>,
Daniel Vetter <daniel@...ll.ch>,
Abhinav Kumar <quic_abhinavk@...cinc.com>,
Sean Paul <sean@...rly.run>,
Thomas Zimmermann <tzimmermann@...e.de>,
Javier Martinez Canillas <javierm@...hat.com>,
Alex Deucher <alexander.deucher@....com>,
Douglas Anderson <dianders@...omium.org>,
Vladimir Lypak <vladimir.lypak@...il.com>,
dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
linux-arm-msm@...r.kernel.org, freedreno@...ts.freedesktop.org
Subject: Re: [PATCH 4/5] drm/msm/dpu1: Account for DSC's bits_per_pixel having
4 fractional bits
On Sat, 1 Oct 2022 at 22:08, Marijn Suijten
<marijn.suijten@...ainline.org> wrote:
>
> According to the comment this DPU register contains the bits per pixel
> as a 6.4 fractional value, conveniently matching the contents of
> bits_per_pixel in struct drm_dsc_config which also uses 4 fractional
> bits. However, the downstream source this implementation was
> copy-pasted from has its bpp field stored _without_ fractional part.
>
> This makes the entire convoluted math obsolete as it is impossible to
> pull those 4 fractional bits out of thin air, by somehow trying to reuse
> the lowest 2 bits of a non-fractional bpp (lsb = bpp % 4??).
>
> The rest of the code merely attempts to keep the integer part a multiple
> of 4, which is rendered useless thanks to data |= dsc->bits_per_pixel <<
> 12; already filling up those bits anyway (but not on downstream).
>
> Fixes: c110cfd1753e ("drm/msm/disp/dpu1: Add support for DSC")
> Signed-off-by: Marijn Suijten <marijn.suijten@...ainline.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> ---
> drivers/gpu/drm/msm/disp/dpu1/dpu_hw_dsc.c | 11 ++---------
> 1 file changed, 2 insertions(+), 9 deletions(-)
--
With best wishes
Dmitry
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