This is a note to let you know that I've just added the patch titled
drm/msm/dsi: Remove useless math in DSC calculations
to the 6.0-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
drm-msm-dsi-remove-useless-math-in-dsc-calculations.patch
and it can be found in the queue-6.0 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 3348f21ae2cc5b4b94a0a5d1c856f69512f2eb13
Author: Marijn Suijten <marijn.suijten@xxxxxxxxxxxxxx>
Date: Wed Oct 26 20:28:15 2022 +0200
drm/msm/dsi: Remove useless math in DSC calculations
[ Upstream commit 01a907980e0be3310f18c7d4955968f3b28e7147 ]
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@xxxxxxxxxxx>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>
Signed-off-by: Marijn Suijten <marijn.suijten@xxxxxxxxxxxxxx>
Patchwork: https://patchwork.freedesktop.org/patch/508932/
Link: https://lore.kernel.org/r/20221026182824.876933-2-marijn.suijten@xxxxxxxxxxxxxx
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
index 15e108be1901..843521c9cdcf 100644
--- a/drivers/gpu/drm/msm/dsi/dsi_host.c
+++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
@@ -1849,7 +1849,6 @@ 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;
@@ -1929,14 +1928,7 @@ 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;
