From: Marijn Suijten marijn.suijten@somainline.org
[ 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@quicinc.com Reviewed-by: Dmitry Baryshkov dmitry.baryshkov@linaro.org Signed-off-by: Marijn Suijten marijn.suijten@somainline.org Patchwork: https://patchwork.freedesktop.org/patch/508932/ Link: https://lore.kernel.org/r/20221026182824.876933-2-marijn.suijten@somainline.... Signed-off-by: Dmitry Baryshkov dmitry.baryshkov@linaro.org Signed-off-by: Sasha Levin sashal@kernel.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 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;