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Message-ID: <588a89b0-23d5-8d4c-52cb-5f0cfe391e6e@somainline.org>
Date:   Sat, 1 Oct 2022 22:19:23 +0200
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Subject: Re: [PATCH 1/5] drm/msm/dsi: Remove useless math in DSC calculation
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To:     Marijn Suijten <marijn.suijten@somainline.org>,
        phone-devel@vger.kernel.org, Rob Clark <robdclark@gmail.com>,
        Dmitry Baryshkov <dmitry.baryshkov@linaro.org>,
        Vinod Koul <vkoul@kernel.org>
Cc:     ~postmarketos/upstreaming@lists.sr.ht,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@somainline.org>,
        Martin Botka <martin.botka@somainline.org>,
        Jami Kettunen <jami.kettunen@somainline.org>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Abhinav Kumar <quic_abhinavk@quicinc.com>,
        Sean Paul <sean@poorly.run>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        Javier Martinez Canillas <javierm@redhat.com>,
        Alex Deucher <alexander.deucher@amd.com>,
        Douglas Anderson <dianders@chromium.org>,
        Vladimir Lypak <vladimir.lypak@gmail.com>,
        dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
        linux-arm-msm@vger.kernel.org, freedreno@lists.freedesktop.org,
        Marek Vasut <marex@denx.de>
References: <20221001190807.358691-1-marijn.suijten@somainline.org>
 <20221001190807.358691-2-marijn.suijten@somainline.org>
From:   Konrad Dybcio <konrad.dybcio@somainline.org>
In-Reply-To: <20221001190807.358691-2-marijn.suijten@somainline.org>
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On 1.10.2022 21:08, Marijn Suijten wrote:
> Multiplying a value by 2 and adding 1 to it always results in a value
> that is uneven, and that 1 gets truncated immediately when performing
> integer division by 2 again.  There is no "rounding" possible here.
> 
> Fixes: b9080324d6ca ("drm/msm/dsi: add support for dsc data")
> Signed-off-by: Marijn Suijten <marijn.suijten@somainline.org>
> ---
Reviewed-by: Konrad Dybcio <konrad.dybcio@somainline.org>

Konrad
>  drivers/gpu/drm/msm/dsi/dsi_host.c | 7 +------
>  1 file changed, 1 insertion(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
> index 8e4bc586c262..e05bae647431 100644
> --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
> +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
> @@ -1864,12 +1864,7 @@ static int dsi_populate_dsc_params(struct drm_dsc_config *dsc)
>  	data = 2048 * (dsc->rc_model_size - dsc->initial_offset + num_extra_mux_bits);
>  	dsc->slice_bpg_offset = DIV_ROUND_UP(data, groups_total);
>  
> -	/* bpp * 16 + 0.5 */
> -	data = dsc->bits_per_pixel * 16;
> -	data *= 2;
> -	data++;
> -	data /= 2;
> -	target_bpp_x16 = data;
> +	target_bpp_x16 = dsc->bits_per_pixel * 16;
>  
>  	data = (dsc->initial_xmit_delay * target_bpp_x16) / 16;
>  	final_value =  dsc->rc_model_size - data + num_extra_mux_bits;