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SubjectRe: [PATCH v2 1/7] drm/msm/dsi: Remove useless math in DSC calculations
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On 10/5/2022 11:16 AM, 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>
> ---
> 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 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;
>

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