From: Marijn Suijten <marijn.suijten@somainline.org>
To: Abhinav Kumar <quic_abhinavk@quicinc.com>
Cc: David Airlie <airlied@linux.ie>,
Konrad Dybcio <konrad.dybcio@somainline.org>,
dri-devel@lists.freedesktop.org,
Javier Martinez Canillas <javierm@redhat.com>,
AngeloGioacchino Del Regno
<angelogioacchino.delregno@somainline.org>,
phone-devel@vger.kernel.org, Marek Vasut <marex@denx.de>,
Thomas Zimmermann <tzimmermann@suse.de>,
linux-arm-msm@vger.kernel.org,
Dmitry Baryshkov <dmitry.baryshkov@linaro.org>,
Martin Botka <martin.botka@somainline.org>,
~postmarketos/upstreaming@lists.sr.ht,
Sean Paul <sean@poorly.run>,
Jami Kettunen <jami.kettunen@somainline.org>,
Vladimir Lypak <vladimir.lypak@gmail.com>,
Douglas Anderson <dianders@chromium.org>,
linux-kernel@vger.kernel.org, Vinod Koul <vkoul@kernel.org>,
Alex Deucher <alexander.deucher@amd.com>,
freedreno@lists.freedesktop.org
Subject: Re: [Freedreno] [PATCH 1/5] drm/msm/dsi: Remove useless math in DSC calculation
Date: Wed, 5 Oct 2022 00:23:17 +0200 [thread overview]
Message-ID: <20221004222317.6or3w6vwgyd3yy6z@SoMainline.org> (raw)
In-Reply-To: <7ded0eb3-ef99-1979-ffb6-c639288bd863@quicinc.com>
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@somainline.org>
> > ---
> > 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;
next prev parent reply other threads:[~2022-10-04 22:23 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-01 19:08 [PATCH 0/5] drm: Fix math issues in MSM DSC implementation Marijn Suijten
2022-10-01 19:08 ` [PATCH 1/5] drm/msm/dsi: Remove useless math in DSC calculation Marijn Suijten
2022-10-01 20:19 ` Konrad Dybcio
2022-10-04 0:26 ` Bjorn Andersson
2022-10-04 14:33 ` [Freedreno] " Abhinav Kumar
2022-10-04 22:23 ` Marijn Suijten [this message]
2022-10-01 19:08 ` [PATCH 2/5] drm/msm/dsi: Remove repeated calculation of slice_per_intf Marijn Suijten
2022-10-01 20:22 ` Konrad Dybcio
2022-10-04 0:30 ` Bjorn Andersson
2022-10-04 14:41 ` Abhinav Kumar
2022-10-01 19:08 ` [PATCH 3/5] drm/msm/dsi: Account for DSC's bits_per_pixel having 4 fractional bits Marijn Suijten
2022-10-01 20:28 ` Konrad Dybcio
2022-10-01 20:37 ` Marijn Suijten
2022-10-04 14:45 ` Dmitry Baryshkov
2022-10-04 22:35 ` Marijn Suijten
2022-10-04 22:40 ` Dmitry Baryshkov
2022-10-04 22:56 ` Marijn Suijten
2022-10-01 19:08 ` [PATCH 4/5] drm/msm/dpu1: " Marijn Suijten
2022-10-04 14:35 ` Dmitry Baryshkov
2022-10-04 17:03 ` Abhinav Kumar
2022-10-04 22:11 ` Marijn Suijten
2022-10-05 14:19 ` Abhinav Kumar
2022-10-05 18:45 ` Marijn Suijten
2022-10-01 19:08 ` [PATCH 5/5] drm/dsc: Prevent negative BPG offsets from shadowing adjacent bitfields Marijn Suijten
2022-10-01 20:23 ` Marijn Suijten
2022-10-04 14:41 ` Dmitry Baryshkov
2022-10-04 21:48 ` Marijn Suijten
2022-10-04 20:22 ` Abhinav Kumar
2022-10-04 21:57 ` Marijn Suijten
2022-10-04 22:31 ` Abhinav Kumar
2022-10-04 22:39 ` Marijn Suijten
2022-10-05 15:33 ` Abhinav Kumar
2022-10-05 18:29 ` Marijn Suijten
2022-10-04 4:42 ` [PATCH 0/5] drm: Fix math issues in MSM DSC implementation Vinod Koul
2022-10-04 9:51 ` Marijn Suijten
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