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 6.1-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-6.1 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit f099ce4c6f45726272b92dc7140c056787d718a4 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 7fbf391c024f..8026fe65bff6 100644 --- a/drivers/gpu/drm/msm/dsi/dsi_host.c +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c @@ -1762,7 +1762,6 @@ 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; @@ -1842,14 +1841,7 @@ 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;