linux-kernel - [PATCH v4 01/10] drm/msm/dsi: Remove useless math in DSC calculations

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Date:   Wed, 26 Oct 2022 20:28:15 +0200
From:   Marijn Suijten <marijn.suijten@...ainline.org>
To:     phone-devel@...r.kernel.org, Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.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>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Martin Botka <martin.botka@...ainline.org>,
        Jami Kettunen <jami.kettunen@...ainline.org>,
        Marijn Suijten <marijn.suijten@...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: [PATCH v4 01/10] drm/msm/dsi: Remove useless math in DSC calculations

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.

After that target_bpp_x16 is used to store a multiplication of
bits_per_pixel by 16 which is only ever read to immediately be divided
by 16 again, and is elided in much the same way.

Fixes: b9080324d6ca ("drm/msm/dsi: add support for dsc data")
Reviewed-by: Abhinav Kumar <quic_abhinavk@...cinc.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Signed-off-by: Marijn Suijten <marijn.suijten@...ainline.org>
---
 drivers/gpu/drm/msm/dsi/dsi_host.c | 10 +---------
 1 file changed, 1 insertion(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
index e82eef031ed4..d645fcbb0683 100644
--- a/drivers/gpu/drm/msm/dsi/dsi_host.c
+++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
@@ -1784,7 +1784,6 @@ static int dsi_populate_dsc_params(struct drm_dsc_config *dsc)
 	int hrd_delay;
 	int pre_num_extra_mux_bits, num_extra_mux_bits;
 	int slice_bits;
-	int target_bpp_x16;
 	int data;
 	int final_value, final_scale;
 	int i;
@@ -1864,14 +1863,7 @@ 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;
-
-	data = (dsc->initial_xmit_delay * target_bpp_x16) / 16;
+	data = dsc->initial_xmit_delay * dsc->bits_per_pixel;
 	final_value =  dsc->rc_model_size - data + num_extra_mux_bits;
 	dsc->final_offset = final_value;
 
-- 
2.38.1