On 2022-10-04 07:33:49, Abhinav Kumar wrote:
>
>
> On 10/1/2022 12:08 PM, 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.
> >
> > Fixes: b9080324d6ca ("drm/msm/dsi: add support for dsc data")
> > Signed-off-by: Marijn Suijten <marijn.suijten@xxxxxxxxxxxxxx>
> > ---
> > drivers/gpu/drm/msm/dsi/dsi_host.c | 7 +------
> > 1 file changed, 1 insertion(+), 6 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
> > index 8e4bc586c262..e05bae647431 100644
> > --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
> > +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
> > @@ -1864,12 +1864,7 @@ 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;
> > + target_bpp_x16 = dsc->bits_per_pixel * 16;
> >
> Since this patch is titled, "remove useless math", even the
> target_bpp_x16 math looks redundant to me,
>
> first we do
>
> target_bpp_x16 = dsc->bits_per_pixel * 16;
>
> then in the next line we do
>
> data = (dsc->initial_xmit_delay * target_bpp_x16) / 16;
>
> the *16 and /16 will cancel out here.
>
> Instead we can just do
>
> data = (dsc->initial_xmit_delay * dsc->drm->bits_per_pixel) ?
Thanks, good catch! I might have been so focused on explaining the
effect of this patch and uselessness of the proposed `+ 0.5` rounding
here that I missed this intermediate variable now becoming redundant as
well.
Corrected for v2!
- Marijn
> > data = (dsc->initial_xmit_delay * target_bpp_x16) / 16;
> > final_value = dsc->rc_model_size - data + num_extra_mux_bits;
