| Message ID | 20221009184824.457416-2-marijn.suijten@somainline.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | drm/msm: Fix math issues in MSM DSC implementation | expand |
On 09/10/2022 21:48, 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. > > 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") > Signed-off-by: Marijn Suijten <marijn.suijten@somainline.org> > Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com> Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c index 8e4bc586c262..70077d1f0f21 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;
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") Signed-off-by: Marijn Suijten <marijn.suijten@somainline.org> Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com> --- drivers/gpu/drm/msm/dsi/dsi_host.c | 10 +--------- 1 file changed, 1 insertion(+), 9 deletions(-)