linux-kernel - Re: [PATCH 1/5] drm/msm/dsi: Remove useless math in DSC calculation

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Date:   Sat, 1 Oct 2022 22:19:23 +0200
From:   Konrad Dybcio <konrad.dybcio@...ainline.org>
To:     Marijn Suijten <marijn.suijten@...ainline.org>,
        phone-devel@...r.kernel.org, Rob Clark <robdclark@...il.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Vinod Koul <vkoul@...nel.org>
Cc:     ~postmarketos/upstreaming@...ts.sr.ht,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...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,
        Marek Vasut <marex@...x.de>
Subject: Re: [PATCH 1/5] drm/msm/dsi: Remove useless math in DSC calculation



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@...ainline.org>
> ---
Reviewed-by: Konrad Dybcio <konrad.dybcio@...ainline.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;